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Jandová M, Fišerová M, Paterová P, Cacková L, Měřička P, Malý J, Kacerovský M, Kovaříková E, Strohalm J, Demnerová K, Kadavá J, Sýkorová H, Hyšpler R, Čížková D, Bezrouk A, Houška M. High-Pressure Inactivation of Bacillus cereus in Human Breast Milk. Foods 2023; 12:4245. [PMID: 38231674 DOI: 10.3390/foods12234245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 11/20/2023] [Accepted: 11/21/2023] [Indexed: 01/19/2024] Open
Abstract
Although Holder pasteurization is the recommended method for processing breast milk, it does affect some of its nutritional and biological properties and is ineffective at inactivating spores. The aim of this study was to find and validate an alternative methodology for processing breast milk to increase its availability for newborn babies and reduce the financial loss associated with discarding milk that has become microbiologically positive. We prepared two series of breast milk samples inoculated with the Bacillus cereus (B. cereus) strain to verify the effectiveness of two high-pressure treatments: (1) 350 MPa/5 min/38 °C in four cycles and (2) cumulative pressure of 350 MPa/20 min/38 °C. We found that the use of pressure in cycles was statistically more effective than cumulative pressure. It reduced the number of spores by three to four orders of magnitude. We verified that the method was reproducible. The routine use of this method could lead to an increased availability of milk for newborn babies, and at the same time, reduce the amount of wasted milk. In addition, high-pressure treatment preserves the nutritional quality of milk.
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Affiliation(s)
- Miroslava Jandová
- Tissue Bank, University Hospital Hradec Králové, 500 05 Hradec Králové, Czech Republic
- Department of Histology and Embryology, Faculty of Medicine in Hradec Králové, Charles University, 500 03 Hradec Králové, Czech Republic
| | - Michaela Fišerová
- Tissue Bank, University Hospital Hradec Králové, 500 05 Hradec Králové, Czech Republic
| | - Pavla Paterová
- Department of Clinical Microbiology, University Hospital and Faculty of Medicine in Hradec Králové, Charles University, 500 05 Hradec Králové, Czech Republic
| | - Lucie Cacková
- Department of Clinical Microbiology, University Hospital and Faculty of Medicine in Hradec Králové, Charles University, 500 05 Hradec Králové, Czech Republic
| | - Pavel Měřička
- Tissue Bank, University Hospital Hradec Králové, 500 05 Hradec Králové, Czech Republic
| | - Jan Malý
- Department of Pediatrics, University Hospital Hradec Králové, 500 05 Hradec Králové, Czech Republic
| | - Marian Kacerovský
- Biomedical Research Center, University Hospital Hradec Králové, 500 05 Hradec Králové, Czech Republic
| | | | - Jan Strohalm
- Food Research Institute Prague, 102 00 Prague, Czech Republic
| | - Kateřina Demnerová
- Department of Biochemistry and Microbiology, University of Chemistry and Technology Prague, 166 28 Prague, Czech Republic
| | - Jana Kadavá
- Department of Biochemistry and Microbiology, University of Chemistry and Technology Prague, 166 28 Prague, Czech Republic
| | - Hana Sýkorová
- Department of Biochemistry and Microbiology, University of Chemistry and Technology Prague, 166 28 Prague, Czech Republic
| | - Radomír Hyšpler
- Department of Clinical Biochemistry and Diagnostics, University Hospital Hradec Králové, 500 05 Hradec Králové, Czech Republic
| | - Dana Čížková
- Department of Histology and Embryology, Faculty of Medicine in Hradec Králové, Charles University, 500 03 Hradec Králové, Czech Republic
| | - Aleš Bezrouk
- Department of Medical Biophysics, Faculty of Medicine in Hradec Králové, Charles University, 500 03 Hradec Králové, Czech Republic
| | - Milan Houška
- Food Research Institute Prague, 102 00 Prague, Czech Republic
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Vittoria M, Saggese A, Di Gregorio Barletta G, Castaldi S, Isticato R, Baccigalupi L, Ricca E. Sporulation efficiency and spore quality in a human intestinal isolate of Bacillus cereus. Res Microbiol 2023; 174:104030. [PMID: 36738815 DOI: 10.1016/j.resmic.2023.104030] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 01/18/2023] [Accepted: 01/20/2023] [Indexed: 02/05/2023]
Abstract
Bacteria classified as Bacillus cereus sensu stricto cause two different type of gastrointestinal diseases associated with food poisoning. Outbreaks of this opportunistic pathogen are generally due to the resistance of its spores to heat, pH and desiccation that makes hard their complete inactivation from food products. B. cereus is commonly isolated from a variety of environments, including intestinal samples of infected and healthy people. We report the genomic and physiological characterization of MV19, a human intestinal strain closely related (ANI value of 98.81%) to the reference strain B. cereus ATCC 14579. MV19 cells were able to grow in a range of temperatures between 20 and 44 °C. At the optimal temperature the sporulation process was rapidly induced and mature spores efficiently released, however these appeared structurally and morphologically defective. At the sub-optimal growth temperature of 25 °C sporulation was slow and less efficient but a high total number of fully functional spores was produced. These results indicate that the reduced rapidity and efficiency of sporulation at 25 °C are compensated by a high quality and quantity of released spores, suggesting the relevance of different performances at different growth conditions for the adaptation of this bacterium to diverse environmental niches.
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Affiliation(s)
- Maria Vittoria
- Department of Biology, Federico II University of Naples, Italy
| | - Anella Saggese
- Department of Biology, Federico II University of Naples, Italy
| | | | | | | | - Loredana Baccigalupi
- Department of Molecular Medicine and Medical Biotechnology, Federico II University of Naples, Italy
| | - Ezio Ricca
- Department of Biology, Federico II University of Naples, Italy.
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Heydenreich R, Delbrück AI, Mathys A. Post-high-pressure temperature and time - Overlooked parameters in high pressure treatment of bacterial spores. Int J Food Microbiol 2023; 402:110279. [PMID: 37331115 DOI: 10.1016/j.ijfoodmicro.2023.110279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Revised: 05/19/2023] [Accepted: 06/03/2023] [Indexed: 06/20/2023]
Abstract
High pressure (HP) processing has high potential for bacterial spore inactivation with minimal thermal input. To advance HP germination and subsequent inactivation of spores, this study explored the physiological state of HP-treated spores using flow cytometry (FCM). Bacillus subtilis spores were treated at 550 MPa and 60 °C (very HP (vHP)) in buffer, incubated after the HP treatment, and stained for FCM analysis with SYTO16 indicating germination and propidium iodide (PI) indicating membrane damage. FCM subpopulations were analyzed depending on the HP dwell time (≤20 min), post-HP temperature (ice, 37 °C, 60 °C) and time (≤4 h), germination-relevant cortex-lytic enzymes (CLEs) and small-acid-soluble-proteins-(SASP)-degrading enzymes by using deletion strains. The effect of post-HP temperatures (ice, 37 °C) was additionally studied for moderate HP (150 MPa, 38 °C, 10 min). Post-HP incubation conditions strongly influenced the prevalence of five observed FCM subpopulations. Post-HP incubation on ice did not or only slowly shifted SYTO16-positive spores to higher SYTO16 levels. At 37 °C post-HP, this shift accelerated, and a shift to high PI intensities occurred depending on the HP dwell time. At 60 °C post-HP, the main shift was from SYTO16-positive to PI-positive subpopulations. The enzymes CwlJ and SleB, which are CLEs, seemed both necessary for PI or SYTO16 uptake, and to have different sensitivities to 550 MPa and 60 °C. Different extents of SASP degradation might explain the existence of two SYTO16-positive subpopulations. Shifts to higher SYTO16 intensities during post-HP incubation on ice or at 37 °C might rely on the activity and recovery of CLEs, SASP-degrading enzymes or their associated proteins from reversible HP-induced structural changes. These enzymes seemingly become active only during decompression or after vHP treatments (550 MPa, 60 °C). Based on our results, we provide a refined model of HP germination-inactivation of B. subtilis spores and an optimized FCM method for quantification of the safety-relevant subpopulation, i.e., vHP (550 MPa, 60 °C) superdormant spores. This study contributes to the development of mild spore inactivation processes by shedding light on overlooked parameters: post-HP incubation conditions. Post-HP conditions significantly influenced the physiological state of spores, likely due to varying enzymatic activity. This finding may explain inconsistencies in previous research and shows the importance of reporting post-HP conditions in future research. Furthermore, the addition of post-HP conditions as HP process parameter may open up new possibilities to optimize HP-based inactivation of spores for potential industrial applications in the food industry.
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Affiliation(s)
- Rosa Heydenreich
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zurich, Zurich, Switzerland
| | - Alessia I Delbrück
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zurich, Zurich, Switzerland
| | - Alexander Mathys
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zurich, Zurich, Switzerland.
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CotG Mediates Spore Surface Permeability in Bacillus subtilis. mBio 2022; 13:e0276022. [PMID: 36354330 PMCID: PMC9765600 DOI: 10.1128/mbio.02760-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Proteins and glycoproteins that form the surface layers of the Bacillus spore assemble into semipermeable arrays that surround and protect the spore cytoplasm. Such layers, acting like molecular sieves, exclude large molecules but allow small nutrients (germinants) to penetrate. We report that CotG, a modular and abundant component of the Bacillus subtilis spore coat, controls spore permeability through its central region, formed by positively charged tandem repeats. These repeats act as spacers between the N and C termini of the protein, which are responsible for the interaction of CotG with at least one other coat protein. The deletion but not the replacement of the central repeats with differently charged repeats affects the spore resistance to lysozyme and the efficiency of germination-probably by reducing the coat permeability to external molecules. The presence of central repeats is a common feature of the CotG-like proteins present in most Bacillus species, and such a wide distribution of this protein family is suggestive of a relevant role for the structure and function of the Bacillus spore. IMPORTANCE Bacterial spores are quiescent cells extremely resistant to a variety of unphysiological conditions, including the presence of lytic enzymes. Such resistance is also due to the limited permeability of the spore surface, which does not allow lytic enzymes to reach the spore interior. This article proposes that the spore permeability in B. subtilis is mediated by CotG, a modular protein formed by a central region of repeats of positively charged amino acid acting as a "spacer" between the N and C termini. These, in turn, interact with other coat proteins, generating a protein layer whose permeability to external molecules is controlled by the distance between the N and C termini of CotG. This working model is most likely expandable to most sporeformers of the Bacillus genus, since they all have CotG-like proteins, not homologous to CotG of B. subtilis but similarly characterized by central repeats.
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5
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A microbiological perspective of raw milk preserved at room temperature using hyperbaric storage compared to refrigerated storage. INNOV FOOD SCI EMERG 2022. [DOI: 10.1016/j.ifset.2022.103019] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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6
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Pang Y, Wu R, Cui T, Zhang Z, Dong L, Chen F, Hu X. Proteomic Response of Bacillus subtilis Spores under High Pressure Combined with Moderate Temperature and Random Peptide Mixture LK Treatment. Foods 2022; 11:foods11081123. [PMID: 35454710 PMCID: PMC9030791 DOI: 10.3390/foods11081123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Revised: 03/31/2022] [Accepted: 04/08/2022] [Indexed: 11/20/2022] Open
Abstract
In this study, a method of Bacillus subtilis spore inactivation under high pressure (P, 200 MPa) combined with moderate temperature (T, 80 °C) and the addition of antimicrobial peptide LK (102 μg/mL) was investigated. Spores presented cortex hydrolysis and inner membrane (IM) damage with an 8.16 log reduction in response to treatment with PT-LK, as observed by phase-contrast and inverted fluorescence microscopy and flow cytometry (FCM) analysis. Furthermore, a tandem mass tag (TMT) quantitative proteomics approach was utilized because Liquid chromatography-tandem mass spectrometry (LC–MS/MS) analysis data were used. After treatment with PT-LK, 17,017 polypeptides and 3166 proteins were detected from B. subtilis spores. Among them, 78 proteins showed significant differences in abundance between the PT-LK-treated and control groups, with 49 proteins being upregulated and 29 proteins being downregulated in the PT-LK-treated group. Genetic information processing, metabolism, cellular process, and environmental information processing were the main mechanisms of PT-LK-mediated spore inactivation.
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Affiliation(s)
- Yaru Pang
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China; (Y.P.); (R.W.); (T.C.); (Z.Z.); (L.D.); (F.C.)
- China National Engineering Research Center for Fruit and Vegetable Processing, Beijing 100083, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing 100083, China
- Engineering Research Centre for Fruits and Vegetables Processing, Ministry of Education, Beijing 100083, China
| | - Ruobin Wu
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China; (Y.P.); (R.W.); (T.C.); (Z.Z.); (L.D.); (F.C.)
- China National Engineering Research Center for Fruit and Vegetable Processing, Beijing 100083, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing 100083, China
- Engineering Research Centre for Fruits and Vegetables Processing, Ministry of Education, Beijing 100083, China
| | - Tianlin Cui
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China; (Y.P.); (R.W.); (T.C.); (Z.Z.); (L.D.); (F.C.)
- China National Engineering Research Center for Fruit and Vegetable Processing, Beijing 100083, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing 100083, China
- Engineering Research Centre for Fruits and Vegetables Processing, Ministry of Education, Beijing 100083, China
| | - Zequn Zhang
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China; (Y.P.); (R.W.); (T.C.); (Z.Z.); (L.D.); (F.C.)
- China National Engineering Research Center for Fruit and Vegetable Processing, Beijing 100083, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing 100083, China
- Engineering Research Centre for Fruits and Vegetables Processing, Ministry of Education, Beijing 100083, China
| | - Li Dong
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China; (Y.P.); (R.W.); (T.C.); (Z.Z.); (L.D.); (F.C.)
- China National Engineering Research Center for Fruit and Vegetable Processing, Beijing 100083, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing 100083, China
- Engineering Research Centre for Fruits and Vegetables Processing, Ministry of Education, Beijing 100083, China
| | - Fang Chen
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China; (Y.P.); (R.W.); (T.C.); (Z.Z.); (L.D.); (F.C.)
- China National Engineering Research Center for Fruit and Vegetable Processing, Beijing 100083, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing 100083, China
- Engineering Research Centre for Fruits and Vegetables Processing, Ministry of Education, Beijing 100083, China
| | - Xiaosong Hu
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China; (Y.P.); (R.W.); (T.C.); (Z.Z.); (L.D.); (F.C.)
- China National Engineering Research Center for Fruit and Vegetable Processing, Beijing 100083, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing 100083, China
- Engineering Research Centre for Fruits and Vegetables Processing, Ministry of Education, Beijing 100083, China
- Correspondence: ; Tel.: +86-137-0102-6564
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7
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Heat activation and inactivation of bacterial spores. Is there an overlap? Appl Environ Microbiol 2022; 88:e0232421. [PMID: 35020450 DOI: 10.1128/aem.02324-21] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination, and then inactivating the less heat resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores, and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single spore levels. The heat treatments used were 40-80°C, and for 0-300 min. The results were as follows. 1) Heat activation at 40-70°C promoted L-valine and L-asparagine-glucose-fructose-potassium (AGFK) induced germination in a time dependent manner. 2) The optimal heat activation temperatures for AGFK and L-valine germination via the GerB plus GerK or GerA germinant receptors were 65 and 50-65°C, respectively. 3) Heat inactivation of dormant spores appeared at 70°C, and the heat damage of molecules essential for germination and growth began at 70 and 65°C, respectively. 4) Heat treatment at 75°C resulted in both activation of germination and damage to the germination apparatus, and 80°C treatment caused more pronounced heat damage. 5) For the spores that should withstand adverse environmental temperatures in nature, heat activation seems functional for a subsequent optimal germination process, while heat damage affected both germination and outgrowth. Importance Bacterial spores are thermal resistant structures that can thus survive preservation strategies and revive through the process of spore germination. The more heat resistant spores are the more heterogeneous they germinate upon adding germinants. Upon germination spores can cause food spoilage and cause food intoxication. Here we provide new information on both heat activation and inactivation regimes and their effects on the (heterogeneity of) spore germination.
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Moderate high-pressure superdormancy in Bacillus spores: properties of superdormant spores and proteins potentially influencing moderate high-pressure germination. Appl Environ Microbiol 2021; 88:e0240621. [PMID: 34910565 PMCID: PMC8863042 DOI: 10.1128/aem.02406-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Resistant bacterial spores are a major concern in industrial decontamination processes. An approach known as pressure-mediated germination-inactivation strategy aims to artificially germinate spores by isostatic pressure to mitigate their resistance to inactivation processes. The successful implementation of such a germination-inactivation strategy relies on the germination of all spores. However, germination is heterogeneous, with some “superdormant” spores germinating extremely slowly or not at all. The present study investigated potential underlying reasons for moderate high-pressure (150 MPa; 37°C) superdormancy of Bacillus subtilis spores. The water and dipicolinic acid content of superdormant spores was compared with that of the initial dormant spore population. The results suggest that water and dipicolinic acid content are not major drivers of moderate high-pressure superdormancy. A proteomic analysis was used to identify proteins that were quantified at significantly different levels in superdormant spores. Subsequent validation of the germination capacity of deletion mutants revealed that the presence of protein YhcN is required for efficient moderate high-pressure germination and that proteins MinC, cse60, and SspK may also play a role, albeit a minor one. IMPORTANCE Spore-forming bacteria are ubiquitous in nature and, as a consequence, inevitably enter the food chain or other processing environments. Their presence can lead to significant spoilage or safety-related issues. Intensive treatment is usually required to inactivate them; however, this treatment harms important product quality attributes. A pressure-mediated germination-inactivation approach can balance the need for effective spore inactivation and retention of sensitive ingredients. However, superdormant spores are the bottleneck preventing the successful and safe implementation of such a strategy. An in-depth understanding of moderate high-pressure germination and the underlying causes of superdormancy is necessary to advance the development of mild high pressure-based spore control technologies. The approach used in this work allowed the identification of proteins that have not yet been associated with reduced germination at moderate high pressure. This research paves the way for further studies on the germination and superdormancy mechanisms in spores, assisting the development of mild spore inactivation strategies.
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Fekraoui F, Ferret É, Paniel N, Auvy O, Chamontin C, André S, Simonin H, Perrier-Cornet JM. Cycling versus Continuous High Pressure treatments at moderate temperatures: Effect on bacterial spores? INNOV FOOD SCI EMERG 2021. [DOI: 10.1016/j.ifset.2021.102828] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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10
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Asaithambi N, Singh SK, Singha P. Current status of non-thermal processing of probiotic foods: A review. J FOOD ENG 2021. [DOI: 10.1016/j.jfoodeng.2021.110567] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Delbrück AI, Zhang Y, Heydenreich R, Mathys A. Bacillus spore germination at moderate high pressure: A review on underlying mechanisms, influencing factors, and its comparison with nutrient germination. Compr Rev Food Sci Food Saf 2021; 20:4159-4181. [PMID: 34147040 DOI: 10.1111/1541-4337.12789] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 05/14/2021] [Accepted: 05/18/2021] [Indexed: 02/05/2023]
Abstract
Spore-forming bacteria are resistant to stress conditions owing to their ability to form highly resistant dormant spores. These spores can survive adverse environmental conditions in nature, as well as decontamination processes in the food and related industries. Bacterial spores may return to their vegetative state through a process called germination. As spore germination is critical for the loss of resistance, outgrowth, and development of pathogenicity and spoilage potential, the germination pathway has piqued the interest of the scientific community. The inhibition and induction of germination have critical applications in the food industry. Targeted germination can aid in decreasing the resistance of spores and allow the application of milder inactivation procedures. This germination-inactivation strategy allows better maintenance of important food quality attributes. Different stimuli are reported to trigger germination. Among those, isostatic high pressure (HP) has gained increasing attention due to its potential applications in industrial processes. However, pressure-mediated spore germination is extremely heterogeneous as some spores germinate rapidly, while others exhibit slow germination or do not undergo germination at all. The successful and safe implementation of the germination-inactivation strategy, however, depends on the germination of all spores. Therefore, there is a need to elucidate the mechanisms of HP-mediated germination. This work aimed to critically review the current state of knowledge on Bacillus spore germination at a moderate HP of 50-300 MPa. In this review, the germination mechanism, heterogeneity, and influencing factors have been outlined along with knowledge gaps.
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Affiliation(s)
- Alessia I Delbrück
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zürich, Zurich, Switzerland
| | - Yifan Zhang
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zürich, Zurich, Switzerland
| | - Rosa Heydenreich
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zürich, Zurich, Switzerland
| | - Alexander Mathys
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zürich, Zurich, Switzerland
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Kim JU, Shahbaz HM, Cho J, Lee H, Park J. Inactivation of Bacillus cereus spores using a combined treatment of UV-TiO2 photocatalysis and high hydrostatic pressure. INNOV FOOD SCI EMERG 2021. [DOI: 10.1016/j.ifset.2021.102676] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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13
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Isolation, stability, and characteristics of high-pressure superdormant Bacillus subtilis spores. Int J Food Microbiol 2021; 343:109088. [PMID: 33621831 DOI: 10.1016/j.ijfoodmicro.2021.109088] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 11/15/2020] [Accepted: 01/30/2021] [Indexed: 12/26/2022]
Abstract
Bacterial spores are a major challenge in industrial decontamination processes owing to their extreme resistance. High-pressure (HP) of 150 MPa at 37 °C can trigger the germination of spores, making them lose their extreme resistance. Once their resistance is lost, germinated spores can easily be inactivated by a mild decontamination step. The implementation of this gentle germination-inactivation strategy is hindered by the presence of a subpopulation of so-called high-pressure superdormant (HPSD) spores, which resist germination or germinate only very slowly in response to HP. It is essential to understand the properties of HPSD spores and the underlying causes of superdormancy to tackle superdormant spores and further develop germination-inactivation strategies involving HP. This study investigated factors influencing the prevalence of HPSD spores and successfully isolated them by combining buoyant density centrifugation and fluorescence-activated cell sorting, which allowed further characterisation of HPSD spores for the first time. The prevalence of HPSD spores was shown to be strongly dependent on the HP dwell time, with increasing treatment times reducing their prevalence. Spore mutants lacking major germinant receptors further showed a highly increased prevalence of HPSD spores; 93% of the spores remained dormant even after a prolonged HP dwell time of 40 min. In contrast to nutrient germination, sublethal heat treatment of 75 °C for 30 min prior to pressure treatment did not induce spore activation and increase germination. The isolated HPSD spores did not show visible structural differences compared to the initial dormant spores when investigated with transmission electron microscopy. Re-sporulated HPSD spores showed similar germination capacity compared to the initial dormant spores, indicating that HPSD spores are most likely not genetically different from the rest of the population. Moreover, the majority of HPSD spores germinated when exposed a second time to the same germination treatment; however, the germination capacity was lower than that of the initial population. The fact that the majority of spores lost superdormancy when exposed a second time to the same trigger makes it unlikely that there is one factor that determines whether a spore germinates with a certain HP treatment or not. Instead, it seems possible that there are other reversible or cumulative causes. This study investigated the factors influencing spore HP superdormancy to improve the understanding of HPSD spores with regard to their stability, germination capacity, and potential underlying causes of spore HP superdormancy. This knowledge will contribute to the development of HP-based germination-inactivation strategies for gentle but effective spore control.
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14
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Combined high pressure and heat treatment effectively disintegrates spore membranes and inactivates Alicyclobacillus acidoterrestris spores in acidic fruit juice beverage. INNOV FOOD SCI EMERG 2020. [DOI: 10.1016/j.ifset.2020.102523] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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15
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Reineke K, Mathys A. Endospore Inactivation by Emerging Technologies: A Review of Target Structures and Inactivation Mechanisms. Annu Rev Food Sci Technol 2020; 11:255-274. [DOI: 10.1146/annurev-food-032519-051632] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Recent developments in preservation technologies allow for the delivery of food with nutritional value and superior taste. Of special interest are low-acid, shelf-stable foods in which the complete control or inactivation of bacterial endospores is the crucial step to ensure consumer safety. Relevant preservation methods can be classified into physicochemical or physical hurdles, and the latter can be subclassified into thermal and nonthermal processes. The underlying inactivation mechanisms for each of these physicochemical or physical processes impact different morphological or molecular structures essential for spore germination and integrity in the dormant state. This review provides an overview of distinct endospore defense mechanisms that affect emerging physical hurdles as well as which technologies address these mechanisms. The physical spore-inactivation technologies considered include thermal, dynamic, and isostatic high pressure and electromagnetic technologies, such as pulsed electric fields, UV light, cold atmospheric pressure plasma, and high- or low-energy electron beam.
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Affiliation(s)
| | - Alexander Mathys
- Sustainable Food Processing Laboratory, Department of Health Science and Technology, ETH Zurich, CH-8092 Zurich, Switzerland
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Trunet C, Mtimet N, Mathot AG, Postollec F, Leguerinel I, Couvert O, Broussolle V, Carlin F, Coroller L. Suboptimal Bacillus licheniformis and Bacillus weihenstephanensis Spore Incubation Conditions Increase Heterogeneity of Spore Outgrowth Time. Appl Environ Microbiol 2020; 86:e02061-19. [PMID: 31900309 PMCID: PMC7054099 DOI: 10.1128/aem.02061-19] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 12/14/2019] [Indexed: 11/20/2022] Open
Abstract
Changes with time of a population of Bacillus weihenstephanensis KBAB4 and Bacillus licheniformis AD978 dormant spores into germinated spores and vegetative cells were followed by flow cytometry, at pH ranges of 4.7 to 7.4 and temperatures of 10°C to 37°C for B. weihenstephanensis and 18°C to 59°C for B. licheniformis Incubation conditions lower than optimal temperatures or pH led to lower proportions of dormant spores able to germinate and extended time of germination, a lower proportion of germinated spores able to outgrow, an extension of their times of outgrowth, and an increase of the heterogeneity of spore outgrowth time. A model based on the strain growth limits was proposed to quantify the impact of incubation temperature and pH on the passage through each physiological stage. The heat treatment temperature or time acted independently on spore recovery. Indeed, a treatment at 85°C for 12 min or at 95°C for 2 min did not have the same impact on spore germination and outgrowth kinetics of B. weihenstephanensis despite the fact that they both led to a 10-fold reduction of the population. Moreover, acidic sporulation pH increased the time of outgrowth 1.2-fold and lowered the proportion of spores able to germinate and outgrow 1.4-fold. Interestingly, we showed by proteomic analysis that some proteins involved in germination and outgrowth were detected at a lower abundance in spores produced at pH 5.5 than in those produced at pH 7.0, maybe at the origin of germination and outgrowth behavior of spores produced at suboptimal pH.IMPORTANCE Sporulation and incubation conditions have an impact on the numbers of spores able to recover after exposure to sublethal heat treatment. Using flow cytometry, we were able to follow at a single-cell level the changes in the physiological states of heat-stressed spores of Bacillus spp. and to discriminate between dormant spores, germinated spores, and outgrowing vegetative cells. We developed original mathematical models that describe (i) the changes with time of the proportion of cells in their different states during germination and outgrowth and (ii) the influence of temperature and pH on the kinetics of spore recovery using the growth limits of the tested strains as model parameters. We think that these models better predict spore recovery after a sublethal heat treatment, a common situation in food processing and a concern for food preservation and safety.
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Affiliation(s)
- C Trunet
- Univ Brest, Laboratoire Universitaire de Biodiversité et Ecologie Microbienne, UMT ACTIA 19.03 ALTER'iX, Quimper, France
- ADRIA Food Expertise, UMT ACTIA 19.03 ALTER'iX, Quimper, France
| | - N Mtimet
- Univ Brest, Laboratoire Universitaire de Biodiversité et Ecologie Microbienne, UMT ACTIA 19.03 ALTER'iX, Quimper, France
| | - A-G Mathot
- Univ Brest, Laboratoire Universitaire de Biodiversité et Ecologie Microbienne, UMT ACTIA 19.03 ALTER'iX, Quimper, France
| | - F Postollec
- ADRIA Food Expertise, UMT ACTIA 19.03 ALTER'iX, Quimper, France
| | - I Leguerinel
- Univ Brest, Laboratoire Universitaire de Biodiversité et Ecologie Microbienne, UMT ACTIA 19.03 ALTER'iX, Quimper, France
| | - O Couvert
- Univ Brest, Laboratoire Universitaire de Biodiversité et Ecologie Microbienne, UMT ACTIA 19.03 ALTER'iX, Quimper, France
| | - V Broussolle
- INRAE, Avignon Université, UMR SQPOV, Avignon, France
| | - F Carlin
- INRAE, Avignon Université, UMR SQPOV, Avignon, France
| | - L Coroller
- Univ Brest, Laboratoire Universitaire de Biodiversité et Ecologie Microbienne, UMT ACTIA 19.03 ALTER'iX, Quimper, France
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Rao L, Wang Y, Chen F, Hu X, Liao X, Zhao L. High pressure CO2 reduces the wet heat resistance of Bacillus subtilis spores by perturbing the inner membrane. INNOV FOOD SCI EMERG 2020. [DOI: 10.1016/j.ifset.2020.102291] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Zhang Y, Delbrück AI, Off CL, Benke S, Mathys A. Flow Cytometry Combined With Single Cell Sorting to Study Heterogeneous Germination of Bacillus Spores Under High Pressure. Front Microbiol 2020; 10:3118. [PMID: 32038559 PMCID: PMC6985370 DOI: 10.3389/fmicb.2019.03118] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Accepted: 12/24/2019] [Indexed: 01/27/2023] Open
Abstract
Isostatic high pressure (HP) of 150 MPa can trigger the germination of bacterial spores, making them lose their extreme resistance to stress factors, and increasing their susceptibility to milder inactivation strategies. However, germination response of spores within a population is very heterogeneous, and tools are needed to study this heterogeneity. Here, classical methods were combined with more recent and powerful techniques such as flow cytometry (FCM) and fluorescence activated cell sorting (FACS) to investigate spore germination behavior under HP. Bacillus subtilis spores were treated with HP at 150 MPa and 37°C, stained with SYTO16 and PI, and analyzed via FCM. Four sub-populations were detected. These sub-populations were for the first time isolated on single cell level using FACS and characterized in terms of their heat resistance (80°C, 10 min) and cultivability in a nutrient-rich environment. The four isolated sub-populations were found to include (1) heat-resistant and mostly cultivable superdormant spores, i.e., spores that remained dormant after this specific HP treatment, (2) heat-sensitive and cultivable germinated spores, (3) heat-sensitive and partially-cultivable germinated spores, and (4) membrane-compromised cells with barely detectable cultivability. Of particular interest was the physiological state of the third sub-population, which was previously referred to as "unknown". Moreover, the kinetic transitions between different physiological states were characterized. After less than 10 min of HP treatment, the majority of spores germinated and ended up in a sublethally damaged stage. HP treatment at 150 MPa and 37°C did not cause inactivation of all geminated spores, suggesting that subsequent inactivation strategies such as mild heat inactivation or other inactivation techniques are necessary to control spores in food. This study validated FCM as a powerful technique to investigate the heterogeneous behavior of spores under HP, and provided a pipeline using FACS for isolation of different sub-populations and subsequent characterization to understand their physiological states.
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Affiliation(s)
- Yifan Zhang
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zürich, Zurich, Switzerland
| | - Alessia I. Delbrück
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zürich, Zurich, Switzerland
| | - Cosima L. Off
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zürich, Zurich, Switzerland
| | - Stephan Benke
- Cytometry Facility, University of Zurich, Zurich, Switzerland
| | - Alexander Mathys
- Sustainable Food Processing Laboratory, Institute of Food, Nutrition and Health, Department of Health Science and Technology, ETH Zürich, Zurich, Switzerland
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Morimatsu K, Nakaura Y, Inaoka T, Kimura K, Yamamoto K. Effects of Solution pH and Ions on Suicidal Germination of Bacillus subtilis Spores Induced by Medium High Temperature-Medium High Hydrostatic Pressure Treatment. Biocontrol Sci 2020; 24:167-172. [PMID: 31527348 DOI: 10.4265/bio.24.167] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
Abstract
Spores of Bacillus subtilis suspended in water or aqueous solution of NaCl, CaCl2, sodium lactate, or calcium lactate at pH 4 - 7 was subjected to spore inactivation by simultaneous combination of medium high hydrostatic pressure (MHHP; 100 MPa) treatment for germination and medium high temperature (MHT; 65℃) treatment for pasteurization of germinated vegetative cells. The spores at pH 4 in NaCl solution and those at pH 5 and 6 in Na lactate solutions were less killed than in water by MHHP+MHT treatment. Spore inactivation was promoted by calcium ion in NaCl solution at pH 4 and in Na lactate solutions at pH 5 and pH 6, while it was more suppressed at pH 5 and pH 6 in Na lactate solutions than at pH 4 in NaCl solution. The spores treated by MHHP+MHT in NaCl or Na lactate solution at pH 4 were further killed by subsequent MHT treatment.
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Affiliation(s)
- Kazuya Morimatsu
- Department of Food Production Science, Graduate School of Agriculture, Ehime University
| | - Yoshiko Nakaura
- Food Research Institute, National Agriculture and Food Research Organization
| | - Takashi Inaoka
- Food Research Institute, National Agriculture and Food Research Organization
| | - Keitarou Kimura
- Food Research Institute, National Agriculture and Food Research Organization
| | - Kazutaka Yamamoto
- Food Research Institute, National Agriculture and Food Research Organization
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Fan L, Ismail BB, Hou F, Muhammad AI, Zou M, Ding T, Liu D. Thermosonication damages the inner membrane of Bacillus subtilis spores and impels their inactivation. Food Res Int 2019; 125:108514. [DOI: 10.1016/j.foodres.2019.108514] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Revised: 05/25/2019] [Accepted: 06/21/2019] [Indexed: 02/02/2023]
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Importance of Individual Germination Receptor Subunits in the Cooperative Function between GerA and Ynd. J Bacteriol 2019; 201:JB.00451-19. [PMID: 31427390 DOI: 10.1128/jb.00451-19] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Accepted: 08/06/2019] [Indexed: 11/20/2022] Open
Abstract
Germination of Bacillus spores is triggered by the binding of specific nutrients to germinant receptors (GRs) located in the spore's inner membrane. The GRs typically consist of A, B, and C subunits, encoded by tricistronic ger operons. The Bacillus licheniformis genome contains the gerA family operons gerA, ynd, and gerK In contrast to the ABC(D) organization that characterizes gerA operons of many Bacillus species, B. licheniformis genomes contain a pentacistronic ynd operon comprising the yndD, yndE3 , yndE2 , yndF1 , and yndE1 genes encoding A, B, B, C, and B GR subunits, respectively (subscripts indicate paralogs). Here we show that B. licheniformis spores can germinate in the absence of the Ynd and GerK GRs, although cooperation between all three GRs is required for optimal germination with amino acids. Spores carrying an incomplete set of Ynd B subunits demonstrated reduced germination efficiencies, while depletion of all three Ynd B subunits restored germination of the spore population to levels only slightly lower than those of wild-type spores at high germinant concentrations. This suggests that the presence of an incomplete set of Ynd B subunits exhibits a dominant negative effect on germination and that the A and C subunits of the Ynd GR are sufficient for the cooperative functionality between Ynd and GerA. In contrast to the B subunits of Ynd, the B subunit of GerA was essential for amino acid-induced germination. This study provides novel insights into the role of individual GR subunits in the cooperative interaction between GRs in triggering spore germination.IMPORTANCE Spore-forming bacteria are problematic for the food industry, as spores can survive decontamination procedures and subsequently revive in food products, with the risk of food spoilage and foodborne disease. The Ynd and GerA germination receptors (GRs) cooperate in triggering efficient germination of Bacillus licheniformis spores when nutrients are present in the surrounding environment. This study shows that the single B subunit of GerA is essential for the cooperative function between Ynd and GerA, while the three B subunits of the Ynd GR are dispensable. The ability of GRs lacking individual subunits to stimulate germination together with other GRs could explain why ger operons lacking GR subunit genes are maintained in genomes of spore-forming species.
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Liang D, Zhang L, Wang X, Wang P, Liao X, Wu X, Chen F, Hu X. Building of Pressure-Assisted Ultra-High Temperature System and Its Inactivation of Bacterial Spores. Front Microbiol 2019; 10:1275. [PMID: 31244800 PMCID: PMC6579918 DOI: 10.3389/fmicb.2019.01275] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Accepted: 05/22/2019] [Indexed: 11/21/2022] Open
Abstract
The pressure-assisted ultra-high temperature (PAUHT) system was built by using soybean oil as pressure-transmitting medium, and the multiple regression equation of soybean oil temperature change (ΔTP ) during pressurization as a function of initial temperature (Ti ) and set pressure (P) was developed: ΔTP = -13.45 + 0.46 Ti + 0.0799 P - 0.0037T i 2 - 2.83 × 10-5 P2. The fitted model indicated that the temperature of the system would achieve ≥121°C at 600 MPa when the initial temperature of soybean oil was ≥84°C. The PAUHT system could effectively inactivate spores of Bacillus subtilis 168 and Clostridium sporogenes PA3679 (less than 1 min). Treatment of 600 MPa and 121°C with no holding time resulted in a 6.75 log reductions of B. subtilis 168 spores, while treatment of 700 MPa and 121°C with pressure holding time of 20 s achieved more than 5 log reductions of C. sporogenes PA3679 spores. By comparing the PAUHT treatment with high pressure or thermal treatment alone, and also studying the effect of compression on spore inactivation during PAUHT treatment, the inactivation mechanism was further discussed and could be concluded as follows: both B. subtilis 168 and C. sporogenes PA3679 spores were triggered to germinate firstly by high pressure, which was enhanced by increased temperature, then the germinated spores were inactivated by heat.
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Affiliation(s)
- Dong Liang
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing, China
| | - Liang Zhang
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing, China
| | - Xu Wang
- College of Food Science, Northeast Agricultural University, Harbin, China
| | - Pan Wang
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing, China
| | - Xiaojun Liao
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing, China
| | - Xiaomeng Wu
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing, China
| | - Fang Chen
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing, China
| | - Xiaosong Hu
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing, China
- Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Beijing, China
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23
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Lv R, Zou M, Chantapakul T, Chen W, Muhammad AI, Zhou J, Ding T, Ye X, Liu D. Effect of ultrasonication and thermal and pressure treatments, individually and combined, on inactivation of Bacillus cereus spores. Appl Microbiol Biotechnol 2019; 103:2329-2338. [PMID: 30627794 DOI: 10.1007/s00253-018-9559-3] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 11/30/2018] [Accepted: 12/05/2018] [Indexed: 01/03/2023]
Abstract
Bacillus cereus spores are a concern to the food industry due to their high resistance to processing and their ability to germinate to vegetative cells under suitable conditions. This research aimed to elucidate the mechanisms of Bacillus cereus spore inactivation under ultrasonication (US) combined with thermal (thermosonication, TS) treatments, with pressure (manosonication, MS) treatments, and with thermal and pressure (manothermosonication, MTS) treatments. Electronic microscopy, dipicolinic acid (DPA) release, and flow cytometric assessments were used to investigate the inactivation effect and understand the inactivation mechanisms. The sporicidal effects of the US and thermal treatment were slight, and the MS and TS also showed little inactivation effect. However, ultrasonication promoted the detachment of the exosporium, thereby reducing the spore's ability to adhere to a surface, while the thermal treatment induced a decrease in the electron density in the nucleoid of bacterium, which retained a relatively intact exosporium and coat. MS caused 92.54% DPA release, which might be due to triggering of the germinant receptors or releasing of ions and Ca2+-DPA. In addition, the morphological changes such as core hydration and cortex degradation were significant after treatment with MS. The release of DPA and the morphological changes were responsible for the reduction in thermal resistance. The MTS showed a remarkable inactivation effect of 3.12 log CFU/mL reductions after 30 min of treatment. It was the most effective treatment and exhibited a large fraction of damage. In addition, the MTS had a significant impact on the intracellular structure of the spores, with the coat destroyed and the cortex damaged. These results indicated that ultrasonication combined with thermal and pressure treatments had a significant sporicidal effect on Bacillus cereus spores and could be a promising green sterilization technology.
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Affiliation(s)
- Ruiling Lv
- College of Biosystems Engineering and Food Science, National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Zhejiang Key Laboratory for Agro-Food Processing, Zhejiang R and D Center for Food Technology and Equipment, Zhejiang University, 866 Yuhangtang Rd., Hangzhou, 310058, China
| | - Mingming Zou
- College of Biosystems Engineering and Food Science, National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Zhejiang Key Laboratory for Agro-Food Processing, Zhejiang R and D Center for Food Technology and Equipment, Zhejiang University, 866 Yuhangtang Rd., Hangzhou, 310058, China
| | - Thunthacha Chantapakul
- College of Biosystems Engineering and Food Science, National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Zhejiang Key Laboratory for Agro-Food Processing, Zhejiang R and D Center for Food Technology and Equipment, Zhejiang University, 866 Yuhangtang Rd., Hangzhou, 310058, China
| | - Weijun Chen
- College of Biosystems Engineering and Food Science, National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Zhejiang Key Laboratory for Agro-Food Processing, Zhejiang R and D Center for Food Technology and Equipment, Zhejiang University, 866 Yuhangtang Rd., Hangzhou, 310058, China
| | - Aliyu Idris Muhammad
- College of Biosystems Engineering and Food Science, National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Zhejiang Key Laboratory for Agro-Food Processing, Zhejiang R and D Center for Food Technology and Equipment, Zhejiang University, 866 Yuhangtang Rd., Hangzhou, 310058, China
| | - Jianwei Zhou
- College of Biosystems Engineering and Food Science, National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Zhejiang Key Laboratory for Agro-Food Processing, Zhejiang R and D Center for Food Technology and Equipment, Zhejiang University, 866 Yuhangtang Rd., Hangzhou, 310058, China.,Ningbo Institute of Technology, Zhejiang University, Ningbo, 315100, China
| | - Tian Ding
- College of Biosystems Engineering and Food Science, National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Zhejiang Key Laboratory for Agro-Food Processing, Zhejiang R and D Center for Food Technology and Equipment, Zhejiang University, 866 Yuhangtang Rd., Hangzhou, 310058, China
| | - Xingqian Ye
- College of Biosystems Engineering and Food Science, National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Zhejiang Key Laboratory for Agro-Food Processing, Zhejiang R and D Center for Food Technology and Equipment, Zhejiang University, 866 Yuhangtang Rd., Hangzhou, 310058, China
| | - Donghong Liu
- College of Biosystems Engineering and Food Science, National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Zhejiang Key Laboratory for Agro-Food Processing, Zhejiang R and D Center for Food Technology and Equipment, Zhejiang University, 866 Yuhangtang Rd., Hangzhou, 310058, China. .,Fuli Institute of Food Science, Zhejiang University, Hangzhou, 310058, China.
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24
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25
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Buehler A, Martin N, Boor K, Wiedmann M. Psychrotolerant spore-former growth characterization for the development of a dairy spoilage predictive model. J Dairy Sci 2018; 101:6964-6981. [DOI: 10.3168/jds.2018-14501] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Accepted: 04/18/2018] [Indexed: 11/19/2022]
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26
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Lopes RP, Mota MJ, Gomes AM, Delgadillo I, Saraiva JA. Application of High Pressure with Homogenization, Temperature, Carbon Dioxide, and Cold Plasma for the Inactivation of Bacterial Spores: A Review. Compr Rev Food Sci Food Saf 2018; 17:532-555. [PMID: 33350128 DOI: 10.1111/1541-4337.12311] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 08/29/2017] [Accepted: 09/01/2017] [Indexed: 12/18/2022]
Abstract
Formation of highly resistant spores is a concern for the safety of low-acid foods as they are a perfect vehicle for food spoilage and/or human infection. For spore inactivation, the strategy usually applied in the food industry is the intensification of traditional preservation methods to sterilization levels, which is often accompanied by decreases of nutritional and sensory properties. In order to overcome these unwanted side effects in food products, novel and emerging sterilization technologies are being developed, such as pressure-assisted thermal sterilization, high-pressure carbon dioxide, high-pressure homogenization, and cold plasma. In this review, the application of these emergent technologies is discussed, in order to understand the effects on bacterial spores and their inactivation and thus ensure food safety of low-acid foods. In general, the application of these novel technologies for inactivating spores is showing promising results. However, it is important to note that each technique has specific features that can be more suitable for a particular type of product. Thus, the most appropriate sterilization method for each product (and target microorganisms) should be assessed and carefully selected.
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Affiliation(s)
- Rita P Lopes
- QOPNA, Chemistry Dept., Univ. of Aveiro, Campus Univ. de Santiago, 3810-193 Aveiro, Portugal
| | - Maria J Mota
- QOPNA, Chemistry Dept., Univ. of Aveiro, Campus Univ. de Santiago, 3810-193 Aveiro, Portugal
| | - Ana M Gomes
- Escola Superior de Biotecnologia, Univ. Católica Portuguesa, 4200-072 Porto, Portugal
| | - Ivonne Delgadillo
- QOPNA, Chemistry Dept., Univ. of Aveiro, Campus Univ. de Santiago, 3810-193 Aveiro, Portugal
| | - Jorge A Saraiva
- QOPNA, Chemistry Dept., Univ. of Aveiro, Campus Univ. de Santiago, 3810-193 Aveiro, Portugal
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Abstract
Despite being resistant to a variety of environmental insults, the bacterial endospore can sense the presence of small molecules and respond by germinating, losing the specialized structures of the dormant spore, and resuming active metabolism, before outgrowing into vegetative cells. Our current level of understanding of the spore germination process in bacilli and clostridia is reviewed, with particular emphasis on the germinant receptors characterized in Bacillus subtilis, Bacillus cereus, and Bacillus anthracis. The recent evidence for a local clustering of receptors in a "germinosome" would begin to explain how signals from different receptors could be integrated. The SpoVA proteins, involved in the uptake of Ca2+-dipicolinic acid into the forespore during sporulation, are also responsible for its release during germination. Lytic enzymes SleB and CwlJ, found in bacilli and some clostridia, hydrolyze the spore cortex: other clostridia use SleC for this purpose. With genome sequencing has come the appreciation that there is considerable diversity in the setting for the germination machinery between bacilli and clostridia.
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28
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Wang L, Xia Q, Li Y. The effects of high pressure processing and slightly acidic electrolysed water on the structure of Bacillus cereus spores. Food Control 2017. [DOI: 10.1016/j.foodcont.2017.03.036] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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29
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Borch-Pedersen K, Mellegård H, Reineke K, Boysen P, Sevenich R, Lindbäck T, Aspholm M. Effects of High Pressure on Bacillus licheniformis Spore Germination and Inactivation. Appl Environ Microbiol 2017; 83:e00503-17. [PMID: 28476768 PMCID: PMC5494625 DOI: 10.1128/aem.00503-17] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 05/01/2017] [Indexed: 11/20/2022] Open
Abstract
Bacillus and Clostridium species form spores, which pose a challenge to the food industry due to their ubiquitous nature and extreme resistance. Pressurization at <300 MPa triggers spore germination by activating germination receptors (GRs), while pressurization at >300 MPa likely triggers germination by opening dipicolinic acid (DPA) channels present in the inner membrane of the spores. In this work, we expose spores of Bacillus licheniformis, a species associated with food spoilage and occasionally with food poisoning, to high pressure (HP) for holding times of up to 2 h. By using mutant spores lacking one or several GRs, we dissect the roles of the GerA, Ynd, and GerK GRs in moderately HP (mHP; 150 MPa)-induced spore germination. We show that Ynd alone is sufficient for efficient mHP-induced spore germination. GerK also triggers germination with mHP, although at a reduced germination rate compared to that of Ynd. GerA stimulates mHP-induced germination but only in the presence of either the intact GerK or Ynd GR. These results suggests that the effectiveness of the individual GRs in mHP-induced germination differs from their effectiveness in nutrient-induced germination, where GerA plays an essential role. In contrast to Bacillus subtilis spores, treatment with very HP (vHP) of 550 MPa at 37°C did not promote effective germination of B. licheniformis spores. However, treatment with vHP in combination with elevated temperatures (60°C) gave a synergistic effect on spore germination and inactivation. Together, these results provide novel insights into how HP affects B. licheniformis spore germination and inactivation and the role of individual GRs in this process.IMPORTANCE Bacterial spores are inherently resistant to food-processing regimes, such as high-temperature short-time pasteurization, and may therefore compromise food durability and safety. The induction of spore germination facilitates subsequent inactivation by gentler processing conditions that maintain the sensory and nutritional qualities of the food. High-pressure (HP) processing is a nonthermal food-processing technology used to eliminate microbes from food. The application of this technology for spore eradication in the food industry requires a better understanding of how HP affects the spores of different bacterial species. The present study provides novel insights into how HP affects Bacillus licheniformis spores, a species associated with food spoilage and occasionally food poisoning. We describe the roles of different germination receptors in HP-induced germination and the effects of two different pressure levels on the germination and inactivation of spores. This study will potentially contribute to the effort to implement HP technology for spore inactivation in the food industry.
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Affiliation(s)
- Kristina Borch-Pedersen
- Department of Food Safety and Infection Biology, Faculty of Veterinary Medicine, the Norwegian University of Life Sciences, Oslo, Norway
| | - Hilde Mellegård
- Department of Food Safety and Infection Biology, Faculty of Veterinary Medicine, the Norwegian University of Life Sciences, Oslo, Norway
| | - Kai Reineke
- Quality and Safety of Food and Feed, Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB), Potsdam, Germany
| | - Preben Boysen
- Department of Food Safety and Infection Biology, Faculty of Veterinary Medicine, the Norwegian University of Life Sciences, Oslo, Norway
| | - Robert Sevenich
- Department of Food Biotechnology and Food Process Engineering, Technische Universität Berlin, Berlin, Germany
| | - Toril Lindbäck
- Department of Food Safety and Infection Biology, Faculty of Veterinary Medicine, the Norwegian University of Life Sciences, Oslo, Norway
| | - Marina Aspholm
- Department of Food Safety and Infection Biology, Faculty of Veterinary Medicine, the Norwegian University of Life Sciences, Oslo, Norway
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Inaoka T, Kimura K, Morimatsu K, Yamamoto K. Characterization of high hydrostatic pressure-injured Bacillus subtilis cells. Biosci Biotechnol Biochem 2017; 81:1235-1240. [PMID: 28485219 DOI: 10.1080/09168451.2017.1292835] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
High hydrostatic pressure (HHP) affects various cellular processes. Using a sporulation-deficient Bacillus subtilis strain, we characterized the properties of vegetative cells subjected to HHP. When stationary-phase cells were exposed to 250 MPa of HHP for 10 min at 25 °C, approximately 50% of cells were viable, although they exhibited a prolonged growth lag. The HHP-injured cells autolyzed in the presence of NaCl or KCl (at concentrations ≥100 mM). Superoxide dismutase slightly protected the viability of HHP-treated cells, whereas vegetative catalases had no effect. Thus, unlike HHP-injured Escherichia coli, oxidative stress only slightly affected vegetative B. subtilis subjected to HHP.
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Affiliation(s)
- Takashi Inaoka
- a Food Research Institute , National Agriculture and Food Research Organization , Tsukuba , Japan
| | - Keitarou Kimura
- a Food Research Institute , National Agriculture and Food Research Organization , Tsukuba , Japan
| | - Kazuya Morimatsu
- b Department of Food Production Science, Graduate School of Agriculture , Ehime University , Matsuyama , Japan
| | - Kazutaka Yamamoto
- a Food Research Institute , National Agriculture and Food Research Organization , Tsukuba , Japan
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Warda AK, Xiao Y, Boekhorst J, Wells-Bennik MHJ, Nierop Groot MN, Abee T. Analysis of Germination Capacity and Germinant Receptor (Sub)clusters of Genome-Sequenced Bacillus cereus Environmental Isolates and Model Strains. Appl Environ Microbiol 2017; 83:e02490-16. [PMID: 27881417 PMCID: PMC5288832 DOI: 10.1128/aem.02490-16] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2016] [Accepted: 11/17/2016] [Indexed: 12/28/2022] Open
Abstract
Spore germination of 17 Bacillus cereus food isolates and reference strains was evaluated using flow cytometry analysis in combination with fluorescent staining at a single-spore level. This approach allowed for rapid collection of germination data under more than 20 conditions, including heat activation of spores, germination in complex media (brain heart infusion [BHI] and tryptone soy broth [TSB]), and exposure to saturating concentrations of single amino acids and the combination of alanine and inosine. Whole-genome sequence comparison revealed a total of 11 clusters of operons encoding germinant receptors (GRs): GerK, GerI, and GerL were present in all strains, whereas GerR, GerS, GerG, GerQ, GerX, GerF, GerW, and GerZ (sub)clusters showed a more diverse presence/absence in different strains. The spores of tested strains displayed high diversity with regard to their sensitivity and responsiveness to selected germinants and heat activation. The two laboratory strains, B. cereus ATCC 14579 and ATCC 10987, and 11 food isolates showed a good germination response under a range of conditions, whereas four other strains (B. cereus B4085, B4086, B4116, and B4153) belonging to phylogenetic group IIIA showed a very weak germination response even in BHI and TSB media. Germination responses could not be linked to specific (combinations of) GRs, but it was noted that the four group IIIA strains contained pseudogenes or variants of subunit C in their gerL cluster. Additionally, two of those strains (B4086 and B4153) carried pseudogenes in the gerK and gerRI (sub)clusters that possibly affected the functionality of these GRs. IMPORTANCE Germination of bacterial spores is a critical step before vegetative growth can resume. Food products may contain nutrient germinants that trigger germination and outgrowth of Bacillus species spores, possibly leading to food spoilage or foodborne illness. Prediction of spore germination behavior is, however, very challenging, especially for spores of natural isolates that tend to show more diverse germination responses than laboratory strains. The approach used has provided information on the genetic diversity in GRs and corresponding subclusters encoded by B. cereus strains, as well as their germination behavior and possible associations with GRs, and it provides a basis for further extension of knowledge on the role of GRs in B. cereus (group member) ecology and transmission to the host.
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Affiliation(s)
- Alicja K Warda
- TI Food and Nutrition, Wageningen, The Netherlands
- Laboratory of Food Microbiology, Wageningen University & Research, Wageningen, The Netherlands
- Wageningen Food and Biobased Research, Wageningen, The Netherlands
| | - Yinghua Xiao
- TI Food and Nutrition, Wageningen, The Netherlands
- Laboratory of Food Microbiology, Wageningen University & Research, Wageningen, The Netherlands
| | - Jos Boekhorst
- TI Food and Nutrition, Wageningen, The Netherlands
- NIZO Food Research B.V., Ede, The Netherlands
| | - Marjon H J Wells-Bennik
- TI Food and Nutrition, Wageningen, The Netherlands
- NIZO Food Research B.V., Ede, The Netherlands
| | - Masja N Nierop Groot
- TI Food and Nutrition, Wageningen, The Netherlands
- Wageningen Food and Biobased Research, Wageningen, The Netherlands
| | - Tjakko Abee
- TI Food and Nutrition, Wageningen, The Netherlands
- Laboratory of Food Microbiology, Wageningen University & Research, Wageningen, The Netherlands
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Doona CJ, Feeherry FE, Kustin K, Chen H, Huang R, Philip Ye X, Setlow P. A Quasi-chemical Model for Bacterial Spore Germination Kinetics by High Pressure. FOOD ENGINEERING REVIEWS 2017. [DOI: 10.1007/s12393-016-9155-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Rao L, Zhao F, Wang Y, Chen F, Hu X, Liao X. Investigating the Inactivation Mechanism of Bacillus subtilis Spores by High Pressure CO2. Front Microbiol 2016; 7:1411. [PMID: 27656175 PMCID: PMC5013045 DOI: 10.3389/fmicb.2016.01411] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2016] [Accepted: 08/25/2016] [Indexed: 11/29/2022] Open
Abstract
The objective of this study was to investigate the inactivation mechanism of Bacillus subtilis spores by high pressure CO2 (HPCD) processing. The spores of B. subtilis were subjected to heat at 0.1 MPa or HPCD at 6.5-20 MPa, and 64-86°C for 0-120 min. The germination, the permeability of inner membrane (IM) and cortex, the release of pyridine-2, 6-dicarboxylic acid (DPA), and changes in the morphological and internal structures of spores were investigated. The HPCD-treated spores did not lose heat resistance and their DPA release was lower than the inactivation, suggesting that spores did not germinate during HPCD. The flow cytometry analysis suggested that the permeability of the IM and cortex of HPCD-treated spores was increased. Furthermore, the DPA of the HPCD-treated spores were released in parallel with their inactivation and the fluorescence photomicrographs showed that these treated spores were stained by propidium iodide, ensuring that the permeability of IM of spores was increased by HPCD. The scanning electron microscopy photomicrographs showed that spores were crushed into debris or exhibited a hollowness on the surface, and the transmission electron microscopy photomicrographs exhibited an enlarged core, ruptured and indistinguishable IM and a loss of core materials in the HPCD-treated spores, indicating that HPCD damaged the structures of the spores. These findings suggested that HPCD inactivated B. subtilis spores by directly damaging the structure of the spores, rather than inducing germination of the spores.
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Affiliation(s)
- Lei Rao
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Food Science and Nutritional Engineering, China Agricultural UniversityBeijing, China; National Engineering Research Center for Fruit and Vegetable ProcessingBeijing, China; Key Lab of Fruit and Vegetable Processing, Ministry of AgricultureBeijing, China
| | - Feng Zhao
- National Engineering Research Center for Fruit and Vegetable ProcessingBeijing, China; Key Lab of Fruit and Vegetable Processing, Ministry of AgricultureBeijing, China
| | - Yongtao Wang
- National Engineering Research Center for Fruit and Vegetable ProcessingBeijing, China; Key Lab of Fruit and Vegetable Processing, Ministry of AgricultureBeijing, China
| | - Fang Chen
- National Engineering Research Center for Fruit and Vegetable ProcessingBeijing, China; Key Lab of Fruit and Vegetable Processing, Ministry of AgricultureBeijing, China
| | - Xiaosong Hu
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Food Science and Nutritional Engineering, China Agricultural UniversityBeijing, China; National Engineering Research Center for Fruit and Vegetable ProcessingBeijing, China; Key Lab of Fruit and Vegetable Processing, Ministry of AgricultureBeijing, China
| | - Xiaojun Liao
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Food Science and Nutritional Engineering, China Agricultural UniversityBeijing, China; National Engineering Research Center for Fruit and Vegetable ProcessingBeijing, China; Key Lab of Fruit and Vegetable Processing, Ministry of AgricultureBeijing, China
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Effects of High-Pressure Treatment on Spores of Clostridium Species. Appl Environ Microbiol 2016; 82:5287-97. [PMID: 27316969 PMCID: PMC4988188 DOI: 10.1128/aem.01363-16] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Accepted: 06/15/2016] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED This work analyzes the high-pressure (HP) germination of spores of the food-borne pathogen Clostridium perfringens (with inner membrane [IM] germinant receptors [GRs]) and the opportunistic pathogen Clostridium difficile (with no IM GRs), which has growing implications as an emerging food safety threat. In contrast to those of spores of Bacillus species, mechanisms of HP germination of clostridial spores have not been well studied. HP treatments trigger Bacillus spore germination through spores' IM GRs at ∼150 MPa or through SpoVA channels for release of spores' dipicolinic acid (DPA) at ≥400 MPa, and DPA-less spores have lower wet heat resistance than dormant spores. We found that C. difficile spores exhibited no germination events upon 150-MPa treatment and were not heat sensitized. In contrast, 150-MPa-treated unactivated C. perfringens spores released DPA and became heat sensitive, although most spores did not complete germination by fully rehydrating the spore core, but this treatment of heat-activated spores led to almost complete germination and greater heat sensitization. Spores of both clostridial organisms released DPA during 550-MPa treatment, but C. difficile spores did not complete germination and remained heat resistant. Heat-activated 550-MPa-HP-treated C. perfringens spores germinated almost completely and became heat sensitive. However, unactivated 550-MPa-treated C. perfringens spores did not germinate completely and were less heat sensitive than spores that completed germination. Since C. difficile and C. perfringens spores use different mechanisms for sensing germinants, our results may allow refinement of HP methods for their inactivation in foods and other applications and may guide the development of commercially sterile low-acid foods. IMPORTANCE Spores of various clostridial organisms cause human disease, sometimes due to food contamination by spores. Because of these spores' resistance to normal decontamination regimens, there is continued interest in ways to kill spores without compromising food quality. High hydrostatic pressure (HP) under appropriate conditions can inactivate bacterial spores. With growing use of HP for food pasteurization, advancement of HP for commercial production of sterile low-acid foods requires understanding of mechanisms of spores' interactions with HP. While much is known about HP germination and inactivation of spores of Bacillus species, how HP germinates and inactivates clostridial spores is less well understood. In this work we have tried to remedy this information deficit by examining germination of spores of Clostridium difficile and Clostridium perfringens by several HP and temperature levels. The results may give insight that could facilitate more efficient methods for spore eradication in food sterilization or pasteurization, biodecontamination, and health care.
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Inhibition of nutrient- and high pressure-induced germination of Bacillus cereus spores by plant essential oils. INNOV FOOD SCI EMERG 2016. [DOI: 10.1016/j.ifset.2016.02.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Sevenich R, Reineke K, Hecht P, Fröhling A, Rauh C, Schlüter O, Knorr D. Impact of different water activities (a w) adjusted by solutes on high pressure high temperature inactivation of Bacillus amyloliquefaciens spores. Front Microbiol 2015. [PMID: 26217321 PMCID: PMC4491632 DOI: 10.3389/fmicb.2015.00689] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Much research has been conducted to comprehend the mechanisms of high pressure (HP) inactivation of spores in aqueous systems but for food model systems these information are scarce. In these systems spores can interact with ingredients which then could possibly lead to retarded or reduced inactivation, which can cause a problem for the sterilization process. The protective mechanism of a reduced aw-value is still unclear. HP processing might prove valuable to overcome protective effects of solutes and achieve shorter process times for sterilization under HP. To gain insight into the underlying mechanisms five aw-values (0.9, 0.92, 0.94, 0.96, 1) were adjusted with two different solutes (NaCl, sucrose). Solutions were inoculated with spores of Bacillus amyloliquefaciens and treated at 105, 110, and 115°C at 600 MPa. Further a thermal inactivation was conducted at the same temperatures for a comparison with the HP data. Afterward, the influence of HP high temperature treatment on the inactivation, the dipicolinic acid (DPA)-release and membrane constitution was assessed by plate count, HPLC and flow cytometry (FCM). The results show that during HP treatments sucrose and salt both have a protective effect, in which the influence of sucrose on the retarded inactivation is higher. The threshold water activities (aw), which is 0.94, here salt and sucrose have a significant influence on the inactivation. The comparison of thermal (105–115°C) and HP and high temperature (600 MPa, 105–115°C) treated samples showed that the time needed to achieve a 4–5 log10 inactivation is reduced from 45 (aw = 1) to 75 (aw = 0.9) min at 105°C to 3 (aw = 1) to 15 (aw = 0.9) minutes at 600 MPa and 105°C. The release of DPA is the rate limiting step of the inactivation and therefore monitoring the release is of great interest. The DPA-release is slowed down in high concentrated solutions (e.g., sucrose, salt) in comparison to aw 1. Since there is a difference in the way the solutes protect the spore it could be seen as an inner spore membrane effect. Maybe as shown for vegetative microorganism the solutes can interact with membranes, e.g., the inner spore membrane. Flow cytometry (FCM) measurement data show a similar trend.
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Affiliation(s)
- Robert Sevenich
- Department of Food Biotechnology and Food Process Engineering, Technische Universität Berlin, Berlin Germany
| | - Kai Reineke
- Leibniz Institute for Agriculture Engineering (ATB), Potsdam Germany
| | - Philipp Hecht
- Department of Food Biotechnology and Food Process Engineering, Technische Universität Berlin, Berlin Germany
| | - Antje Fröhling
- Leibniz Institute for Agriculture Engineering (ATB), Potsdam Germany
| | - Cornelia Rauh
- Department of Food Biotechnology and Food Process Engineering, Technische Universität Berlin, Berlin Germany
| | - Oliver Schlüter
- Leibniz Institute for Agriculture Engineering (ATB), Potsdam Germany
| | - Dietrich Knorr
- Department of Food Biotechnology and Food Process Engineering, Technische Universität Berlin, Berlin Germany
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Lenz CA, Reineke K, Knorr D, Vogel RF. High pressure thermal inactivation of Clostridium botulinum type E endospores - kinetic modeling and mechanistic insights. Front Microbiol 2015; 6:652. [PMID: 26191048 PMCID: PMC4490342 DOI: 10.3389/fmicb.2015.00652] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Accepted: 06/15/2015] [Indexed: 12/03/2022] Open
Abstract
Cold-tolerant, neurotoxigenic, endospore forming Clostridium (C.) botulinum type E belongs to the non-proteolytic physiological C. botulinum group II, is primarily associated with aquatic environments, and presents a safety risk for seafood. High pressure thermal (HPT) processing exploiting the synergistic effect of pressure and temperature can be used to inactivate bacterial endospores. We investigated the inactivation of C. botulinum type E spores by (near) isothermal HPT treatments at 300–1200 MPa at 30–75°C for 1 s to 10 min. The occurrence of heat and lysozyme susceptible spore fractions after such treatments was determined. The experimental data were modeled to obtain kinetic parameters and represented graphically by isoeffect lines. In contrast to findings for spores of other species and within the range of treatment parameters applied, zones of spore stabilization (lower inactivation than heat treatments alone), large heat susceptible (HPT-induced germinated) or lysozyme-dependently germinable (damaged coat layer) spore fractions were not detected. Inactivation followed first order kinetics. Dipicolinic acid release kinetics allowed for insights into possible inactivation mechanisms suggesting a (poorly effective) physiologic-like (similar to nutrient-induced) germination at ≤450 MPa/≤45°C and non-physiological germination at >500 MPa/>60–70°C. Results of this study support the existence of some commonalities in the HPT inactivation mechanism of C. botulinum type E spores and Bacillus spores although both organisms have significantly different HPT resistance properties. The information presented here contributes to closing the gap in knowledge regarding the HPT inactivation of spore formers relevant to food safety and may help industrial implementation of HPT processing. The markedly lower HPT resistance of C. botulinum type E spores compared with the resistance of spores from other C. botulinum types could allow for the implementation of milder processes without endangering food safety.
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Affiliation(s)
- Christian A Lenz
- Lehrstuhl für Technische Mikrobiologie, Technische Universität München Freising, Germany
| | - Kai Reineke
- Quality and Safety of Food and Feed, Leibniz Institute for Agricultural Engineering (ATB), Potsdam Germany ; Department of Food Biotechnology and Food Process Engineering, Technische Universität Berlin Berlin, Germany
| | - Dietrich Knorr
- Department of Food Biotechnology and Food Process Engineering, Technische Universität Berlin Berlin, Germany
| | - Rudi F Vogel
- Lehrstuhl für Technische Mikrobiologie, Technische Universität München Freising, Germany
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Lenz CA, Vogel RF. Differential effects of sporulation temperature on the high pressure resistance of Clostridium botulinum type E spores and the interconnection with sporulation medium cation contents. Food Microbiol 2015; 46:434-442. [DOI: 10.1016/j.fm.2014.09.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2014] [Revised: 08/09/2014] [Accepted: 09/10/2014] [Indexed: 10/24/2022]
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The effects of heat activation on Bacillus spore germination, with nutrients or under high pressure, with or without various germination proteins. Appl Environ Microbiol 2015; 81:2927-38. [PMID: 25681191 DOI: 10.1128/aem.00193-15] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nutrient germination of spores of Bacillus species occurs through germinant receptors (GRs) in spores' inner membrane (IM) in a process stimulated by sublethal heat activation. Bacillus subtilis spores maximum germination rates via different GRs required different 75 °C heat activation times: 15 min for l-valine germination via the GerA GR and 4 h for germination with the L-asparagine-glucose-fructose-K(+) mixture via the GerB and GerK GRs, with GerK requiring the most heat activation. In some cases, optimal heat activation decreased nutrient concentrations for half-maximal germination rates. Germination of spores via various GRs by high pressure (HP) of 150 MPa exhibited heat activation requirements similar to those of nutrient germination, and the loss of the GerD protein, required for optimal GR function, did not eliminate heat activation requirements for maximal germination rates. These results are consistent with heat activation acting primarily on GRs. However, (i) heat activation had no effects on GR or GerD protein conformation, as probed by biotinylation by an external reagent; (ii) spores prepared at low and high temperatures that affect spores' IM properties exhibited large differences in heat activation requirements for nutrient germination; and (iii) spore germination by 550 MPa of HP was also affected by heat activation, but the effects were relatively GR independent. The last results are consistent with heat activation affecting spores' IM and only indirectly affecting GRs. The 150- and 550-MPa HP germinations of Bacillus amyloliquefaciens spores, a potential surrogate for Clostridium botulinum spores in HP treatments of foods, were also stimulated by heat activation.
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Georget E, Sevenich R, Reineke K, Mathys A, Heinz V, Callanan M, Rauh C, Knorr D. Inactivation of microorganisms by high isostatic pressure processing in complex matrices: A review. INNOV FOOD SCI EMERG 2015. [DOI: 10.1016/j.ifset.2014.10.015] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Abstract
Since the first application of high hydrostatic pressure (HHP) for food preservation more than 100 years ago, a wealth of knowledge has been gained on molecular mechanisms underlying the HHP-mediated destruction of microorganisms. However, one observation made back then is still valid, i.e. that HHP alone is not sufficient for the complete inactivation of bacterial endospores. To achieve "commercial sterility" of low-acid foods, i.e. inactivation of spores capable of growing in a specific product under typical storage conditions, a combination of HHP with other hurdles is required (most effectively with heat (HPT)). Although HPT processes are not yet industrially applied, continuous technical progress and increasing consumer demand for minimally processed, additive-free food with long shelf life, makes HPT sterilization a promising alternative to thermal processing.In recent years, considerable progress has been made in understanding the response of spores of the model organism B. subtilis to HPT treatments and detailed insights into some basic mechanisms in Clostridium species shed new light on differences in the HPT-mediated inactivation of Bacillus and Clostridium spores. In this chapter, current knowledge on sporulation and germination processes, which presents the basis for understanding development and loss of the extreme resistance properties of spores, is summarized highlighting commonalities and differences between Bacillus and Clostridium species. In this context, the effect of HPT treatments on spores, inactivation mechanism and kinetics, the role of population heterogeneity, and influence factors on the results of inactivation studies are discussed.
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Affiliation(s)
- Christian A Lenz
- Lehrstuhl für Technische Mikrobiologie, Technische Universität München, 85354, Freising, Germany
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Luu-Thi H, Corthouts J, Passaris I, Grauwet T, Aertsen A, Hendrickx M, Michiels CW. Carvacrol suppresses high pressure high temperature inactivation of Bacillus cereus spores. Int J Food Microbiol 2014; 197:45-52. [PMID: 25560915 DOI: 10.1016/j.ijfoodmicro.2014.12.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Revised: 10/20/2014] [Accepted: 12/14/2014] [Indexed: 12/30/2022]
Abstract
The inactivation of bacterial spores generally proceeds faster and at lower temperatures when heat treatments are conducted under high pressure, and high pressure high temperature (HPHT) processing is, therefore, receiving an increased interest from food processors. However, the mechanisms of spore inactivation by HPHT treatment are poorly understood, particularly at moderately elevated temperature. In the current work, we studied inactivation of the spores of Bacillus cereus F4430/73 by HPHT treatment for 5 min at 600MPa in the temperature range of 50-100°C, using temperature increments of 5°C. Additionally, we investigated the effect of the natural antimicrobial carvacrol on spore germination and inactivation under these conditions. Spore inactivation by HPHT was less than about 1 log unit at 50 to 70°C, but gradually increased at higher temperatures up to about 5 log units at 100°C. DPA release and loss of spore refractility in the spore population were higher at moderate (≤65°C) than at high (≥70°C) treatment temperatures, and we propose that moderate conditions induced the normal physiological pathway of spore germination resulting in fully hydrated spores, while at higher temperatures this pathway was suppressed and replaced by another mechanism of pressure-induced dipicolinic acid (DPA) release that results only in partial spore rehydration, probably because spore cortex hydrolysis is inhibited. Carvacrol strongly suppressed DPA release and spore rehydration during HPHT treatment at ≤65°C and also partly inhibited DPA release at ≥65°C. Concomitantly, HPHT spore inactivation was reduced by carvacrol at 65-90°C but unaffected at 95-100°C.
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Affiliation(s)
- Hue Luu-Thi
- Laboratory of Food Microbiology, Leuven Food Science and Nutrition Research Center (LFoRCe), Department of Microbial and Molecular Systems (M(2)S), KU Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, Belgium
| | - Jorinde Corthouts
- Laboratory of Food Microbiology, Leuven Food Science and Nutrition Research Center (LFoRCe), Department of Microbial and Molecular Systems (M(2)S), KU Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, Belgium
| | - Ioannis Passaris
- Laboratory of Food Microbiology, Leuven Food Science and Nutrition Research Center (LFoRCe), Department of Microbial and Molecular Systems (M(2)S), KU Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, Belgium
| | - Tara Grauwet
- Laboratory of Food Technology, Leuven Food Science and Nutrition Research Center (LFoRCe), Department of Microbial and Molecular Systems (M(2)S), KU Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, Belgium
| | - Abram Aertsen
- Laboratory of Food Microbiology, Leuven Food Science and Nutrition Research Center (LFoRCe), Department of Microbial and Molecular Systems (M(2)S), KU Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, Belgium
| | - Marc Hendrickx
- Laboratory of Food Technology, Leuven Food Science and Nutrition Research Center (LFoRCe), Department of Microbial and Molecular Systems (M(2)S), KU Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, Belgium
| | - Chris W Michiels
- Laboratory of Food Microbiology, Leuven Food Science and Nutrition Research Center (LFoRCe), Department of Microbial and Molecular Systems (M(2)S), KU Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, Belgium.
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The sps Gene Products Affect the Germination, Hydrophobicity, and Protein Adsorption of Bacillus subtilis Spores. Appl Environ Microbiol 2014; 80:7293-302. [PMID: 25239894 DOI: 10.1128/aem.02893-14] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Accepted: 09/13/2014] [Indexed: 11/20/2022] Open
Abstract
The multilayered surface of the Bacillus subtilis spore is composed of proteins and glycans. While over 70 different proteins have been identified as surface components, carbohydrates associated with the spore surface have not been characterized in detail yet. Bioinformatic data suggest that the 11 products of the sps operon are involved in the synthesis of polysaccharides present on the spore surface, but an experimental validation is available only for the four distal genes of the operon. Here, we report a transcriptional analysis of the sps operon and a functional study performed by constructing and analyzing two null mutants lacking either all or only the promoter-proximal gene of the operon. Our results show that both sps mutant spores apparently have normal coat and crust but have a small germination defect and are more hydrophobic than wild-type spores. We also show that spores lacking all Sps proteins are highly adhesive and form extensive clumps. In addition, sps mutant spores have an increased efficiency in adsorbing a heterologous enzyme, suggesting that hydrophobic force is a major determinant of spore adsorption and indicating that a deep understanding of the surface properties of the spore is essential for its full development as a surface display platform.
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44
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In situ investigation of Geobacillus stearothermophilus spore germination and inactivation mechanisms under moderate high pressure. Food Microbiol 2014; 41:8-18. [DOI: 10.1016/j.fm.2014.01.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 11/21/2013] [Accepted: 01/10/2014] [Indexed: 01/18/2023]
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45
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Doona C, Ghosh S, Feeherry F, Ramirez-Peralta A, Huang Y, Chen H, Setlow P. High pressure germination of Bacillus subtilis
spores with alterations in levels and types of germination proteins. J Appl Microbiol 2014; 117:711-20. [DOI: 10.1111/jam.12557] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 05/18/2014] [Accepted: 05/29/2014] [Indexed: 11/30/2022]
Affiliation(s)
- C.J. Doona
- US Army-Natick Soldier RD&E Center; Warfighter Directorate; Natick MA USA
| | - S. Ghosh
- Department of Molecular Biology and Biophysics; University of Connecticut Health Center; Farmington CT USA
| | - F.F. Feeherry
- US Army-Natick Soldier RD&E Center; Warfighter Directorate; Natick MA USA
| | - A. Ramirez-Peralta
- Department of Molecular Biology and Biophysics; University of Connecticut Health Center; Farmington CT USA
| | - Y. Huang
- Department of Animal and Food Sciences; University of Delaware; Newark DE USA
| | - H. Chen
- Department of Animal and Food Sciences; University of Delaware; Newark DE USA
| | - P. Setlow
- Department of Molecular Biology and Biophysics; University of Connecticut Health Center; Farmington CT USA
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Velásquez J, Schuurman-Wolters G, Birkner JP, Abee T, Poolman B. Bacillus subtilisspore protein SpoVAC functions as a mechanosensitive channel. Mol Microbiol 2014; 92:813-23. [DOI: 10.1111/mmi.12591] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/24/2014] [Indexed: 11/27/2022]
Affiliation(s)
- Jeanette Velásquez
- Department of Biochemistry; Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
- TI Food and Nutrition; Wageningen The Netherlands
| | - Gea Schuurman-Wolters
- Department of Biochemistry; Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
| | - Jan Peter Birkner
- Department of Biochemistry; Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
| | - Tjakko Abee
- TI Food and Nutrition; Wageningen The Netherlands
- Laboratory of Food Microbiology; Wageningen University; Wageningen The Netherlands
| | - Bert Poolman
- Department of Biochemistry; Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
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47
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Xing Y, Li A, Felker DL, Burggraf LW. Nanoscale structural and mechanical analysis of Bacillus anthracis spores inactivated with rapid dry heating. Appl Environ Microbiol 2014; 80:1739-49. [PMID: 24375142 PMCID: PMC3957622 DOI: 10.1128/aem.03483-13] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2013] [Accepted: 12/21/2013] [Indexed: 11/20/2022] Open
Abstract
Effective killing of Bacillus anthracis spores is of paramount importance to antibioterrorism, food safety, environmental protection, and the medical device industry. Thus, a deeper understanding of the mechanisms of spore resistance and inactivation is highly desired for developing new strategies or improving the known methods for spore destruction. Previous studies have shown that spore inactivation mechanisms differ considerably depending upon the killing agents, such as heat (wet heat, dry heat), UV, ionizing radiation, and chemicals. It is believed that wet heat kills spores by inactivating critical enzymes, while dry heat kills spores by damaging their DNA. Many studies have focused on the biochemical aspects of spore inactivation by dry heat; few have investigated structural damages and changes in spore mechanical properties. In this study, we have inactivated Bacillus anthracis spores with rapid dry heating and performed nanoscale topographical and mechanical analysis of inactivated spores using atomic force microscopy (AFM). Our results revealed significant changes in spore morphology and nanomechanical properties after heat inactivation. In addition, we also found that these changes were different under different heating conditions that produced similar inactivation probabilities (high temperature for short exposure time versus low temperature for long exposure time). We attributed the differences to the differential thermal and mechanical stresses in the spore. The buildup of internal thermal and mechanical stresses may become prominent only in ultrafast, high-temperature heat inactivation when the experimental timescale is too short for heat-generated vapor to efficiently escape from the spore. Our results thus provide direct, visual evidences of the importance of thermal stresses and heat and mass transfer to spore inactivation by very rapid dry heating.
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Affiliation(s)
- Yun Xing
- Department of Engineering Physics, Air Force Institute of Technology, Wright-Patterson Air Force Base (WPAFB), Dayton, Ohio, USA
- Oak Ridge Institute for Science and Education (ORISE), Oak Ridge, Tennessee, USA
| | - Alex Li
- Department of Engineering Physics, Air Force Institute of Technology, Wright-Patterson Air Force Base (WPAFB), Dayton, Ohio, USA
| | - Daniel L. Felker
- Department of Systems Engineering & Management, Air Force Institute of Technology, WPAFB, Dayton, Ohio, USA
| | - Larry W. Burggraf
- Department of Engineering Physics, Air Force Institute of Technology, Wright-Patterson Air Force Base (WPAFB), Dayton, Ohio, USA
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Monitoring rates and heterogeneity of high-pressure germination of bacillus spores by phase-contrast microscopy of individual spores. Appl Environ Microbiol 2013; 80:345-53. [PMID: 24162576 DOI: 10.1128/aem.03043-13] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Germination of Bacillus spores with a high pressure (HP) of ∼150 MPa is via activation of spores' germinant receptors (GRs). The HP germination of multiple individual Bacillus subtilis spores in a diamond anvil cell (DAC) was monitored with phase-contrast microscopy. Major conclusions were that (i) >95% of wild-type spores germinated in 40 min in a DAC at ∼150 MPa and 37°C but individual spores' germination kinetics were heterogeneous; (ii) individual spores' HP germination kinetic parameters were similar to those of nutrient-triggered germination with a variable lag time (Tlag) prior to a period of the rapid release (ΔTrelease) of the spores' dipicolinic acid in a 1:1 chelate with Ca(2+) (CaDPA); (iii) spore germination at 50 MPa had longer average Tlag values than that at ∼150 MPa, but the ΔTrelease values at the two pressures were identical and HPs of <10 MPa did not induce germination; (iv) B. subtilis spores that lacked the cortex-lytic enzyme CwlJ and that were germinated with an HP of 150 MPa exhibited average ΔTrelease values ∼15-fold longer than those for wild-type spores, but the two types of spores exhibited similar average Tlag values; and (v) the germination of wild-type spores given a ≥30-s 140-MPa HP pulse followed by a constant pressure of 1 MPa was the same as that of spores exposed to a constant pressure of 140 MPa that was continued for ≥35 min; (vi) however, after short 150-MPa HP pulses and incubation at 0.1 MPa (ambient pressure), spore germination stopped 5 to 10 min after the HP was released. These results suggest that an HP of ∼150 MPa for ≤30 s is sufficient to fully activate spores' GRs, which remain activated at 1 MPa but can deactivate at ambient pressure.
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49
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Modeling of fungal and bacterial spore germination under static and dynamic conditions. Appl Environ Microbiol 2013; 79:6765-75. [PMID: 23995922 DOI: 10.1128/aem.02521-13] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Isothermal germination curves, sigmoid and nonsigmoid, can be described by a variety of models reminiscent of growth models. Two of these, which are consistent with the percent of germinated spores being initially zero, were selected: one, Weibullian (or "stretched exponential"), for more or less symmetric curves, and the other, introduced by Dantigny's group, for asymmetric curves (P. Dantigny, S. P.-M. Nanguy, D. Judet-Correia, and M. Bensoussan, Int. J. Food Microbiol. 146:176-181, 2011). These static models were converted into differential rate models to simulate dynamic germination patterns, which passed a test for consistency. In principle, these and similar models, if validated experimentally, could be used to predict dynamic germination from isothermal data. The procedures to generate both isothermal and dynamic germination curves have been automated and posted as freeware on the Internet in the form of interactive Wolfram demonstrations. A fully stochastic model of individual and small groups of spores, developed in parallel, shows that when the germination probability is constant from the start, the germination curve is nonsigmoid. It becomes sigmoid if the probability monotonically rises from zero. If the probability rate function rises and then falls, the germination reaches an asymptotic level determined by the peak's location and height. As the number of individual spores rises, the germination curve of their assemblies becomes smoother. It also becomes more deterministic and can be described by the empirical phenomenological models.
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Mohapatra BR, La Duc MT. Detecting the dormant: a review of recent advances in molecular techniques for assessing the viability of bacterial endospores. Appl Microbiol Biotechnol 2013; 97:7963-75. [PMID: 23912118 DOI: 10.1007/s00253-013-5115-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Revised: 07/05/2013] [Accepted: 07/09/2013] [Indexed: 10/26/2022]
Abstract
Due to their contribution to gastrointestinal and pulmonary disease, their ability to produce various deadly exotoxins, and their resistance to extreme temperature, pressure, radiation, and common chemical disinfecting agents, bacterial endospores of the Firmicutes phylum are a major concern for public and environmental health. In addition, the hardy and dormant nature of endospores renders them a particularly significant threat to the integrity of robotic extraterrestrial life-detection investigations. To prevent the contamination of critical surfaces with seemingly ubiquitous bacterial endospores, clean rooms maintained at exceedingly stringent cleanliness levels (i.e., fewer than 100,000 airborne particles per ft(3)) are used for surgical procedures, pharmaceutical processing and packaging, and fabrication and assembly of medical devices and spacecraft components. However, numerous spore-forming bacterial species have been reported to withstand typical clean room bioreduction strategies (e.g., UV lights, maintained humidity, paucity of available nutrients), which highlights the need for rapid and reliable molecular methods for detecting, enumerating, and monitoring the incidence of viable endospores. Robust means of evaluating and tracking spore burden not only provide much needed information pertaining to endospore ecophysiology in different environmental niches but also empower decontamination and bioreduction strategies aimed at sustaining the reliability and integrity of clean room environments. An overview of recent molecular advances in detecting and enumerating viable endospores, as well as the expanding phylogenetic diversity of pathogenic and clean room-associated spore-forming bacteria, ensues.
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Affiliation(s)
- Bidyut R Mohapatra
- Biotechnology and Planetary Protection Group, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
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