1
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Trunet C, Vischer N, Coroller L, Brul S. Germination and outgrowth of Bacillus mycoides KBAB4 spores are impacted by environmental pH, quantitatively analyzed at single cell level with sporetracker. Food Microbiol 2024; 121:104509. [PMID: 38637073 DOI: 10.1016/j.fm.2024.104509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Revised: 02/06/2024] [Accepted: 02/24/2024] [Indexed: 04/20/2024]
Abstract
Quantifying spore germination and outgrowth heterogeneity is challenging. Single cell level analysis should provide supplementary knowledge regarding the impact of unfavorable conditions on germination and outgrowth dynamics. This work aimed to quantify the impact of pH on spore germination and outgrowth, investigating the behavior of individual spore crops, produced under optimal and suboptimal conditions. Bacillus mycoides (formerly B. weihenstephanensis) KBAB4 spores, produced at pH 7.4 and at pH 5.5 were incubated at different pH values, from pH 5.2 to 7.4. The spores were monitored by microscopy live imaging, in controlled conditions, at 30 °C. The images were analyzed using SporeTracker, to determine the state of single cells. The impact of pH on germination and outgrowth times and rates was estimated and the correlation between these parameters was quantified. The correlation between germination and outgrowth times was significantly higher at low pH. These results suggest that an environmental pressure highlights the heterogeneity of spore germination and outgrowth within a spore population. Results were consistent with previous observations at population level, now confirmed and extended to single cell level. Therefore, single cell level analyses can be used to quantify the heterogeneity of spore populations, which is of interest in order to control the development of spore-forming bacteria, responsible for food safety issues.
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Affiliation(s)
- C Trunet
- Univ Brest, INRAE, Laboratoire Universitaire de Biodiversité et Écologie Microbienne, F-29000, Quimper, France.
| | - N Vischer
- Laboratory for Molecular Biology and Microbial Food Safety, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, the Netherlands
| | - L Coroller
- Univ Brest, INRAE, Laboratoire Universitaire de Biodiversité et Écologie Microbienne, F-29000, Quimper, France
| | - S Brul
- Laboratory for Molecular Biology and Microbial Food Safety, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, the Netherlands
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2
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Ribis JW, Shen A. Protocol for quantifying the germination properties of individual bacterial endospores using PySpore. STAR Protoc 2023; 4:102678. [PMID: 37910513 PMCID: PMC10630823 DOI: 10.1016/j.xpro.2023.102678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Revised: 08/11/2023] [Accepted: 10/04/2023] [Indexed: 11/03/2023] Open
Abstract
PySpore is a Python program that tracks the germination of individual bacterial endospores. Here, we present a protocol for segmenting spores and quantifying the germination properties of individual bacterial endospores using PySpore. We describe steps for using GUI-based tools to optimize image processing, annotating data, setting gates, and joining datasets for downstream analyses. We then describe procedures for plotting functionality tools without the user needing to modify the underlying code. For complete details on the use and execution of this protocol, please refer to Ribis et al. (2023).1.
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Affiliation(s)
- John W Ribis
- Tufts University School of Medicine, Boston, MA 02111, USA; Tufts University Graduate School of Biomedical Sciences, Boston, MA 02111, USA.
| | - Aimee Shen
- Tufts University School of Medicine, Boston, MA 02111, USA.
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3
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Li YQ, He L, Aryal M, Wicander J, Korza G, Setlow P. Thioflavin-T does not report on electrochemical potential and memory of dormant or germinating bacterial spores. mBio 2023; 14:e0222023. [PMID: 37830807 PMCID: PMC10653816 DOI: 10.1128/mbio.02220-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Accepted: 08/24/2023] [Indexed: 10/14/2023] Open
Abstract
IMPORTANCE Bacillus and Clostridium spores cause food spoilage and disease because of spores' dormancy and resistance to microbicides. However, when spores "come back to life" in germination, their resistance properties are lost. Thus, understanding the mechanisms of spore germination could facilitate the development of "germinate to eradicate" strategies. One germination feature is the memory of a pulsed germinant stimulus leading to greater germination following a second pulse. Recent observations of increases in spore binding of the potentiometric dye thioflavin-T early in their germination of spores led to the suggestion that increasing electrochemical potential is how spores "remember" germinant pulses. However, new work finds no increased thioflavin-T binding in the physiological germination of Coatless spores or of intact spores germinating with dodecylamine, even though spore memory is seen in both cases. Thus, using thioflavin-T uptake by germinating spores to assess the involvement of electrochemical potential in memory of germinant exposure, as suggested recently, is questionable.
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Affiliation(s)
- Yong-qing Li
- School of Electrical Engineering and Intelligentization, Dongguan University of Technology, Dongguan, Guangdong, China
- Department of Physics, East Carolina University, Greenville, North Carolina, USA
| | - Lin He
- School of Electrical Engineering and Intelligentization, Dongguan University of Technology, Dongguan, Guangdong, China
| | - Makunda Aryal
- Department of Physics, East Carolina University, Greenville, North Carolina, USA
| | - James Wicander
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, Connecticut, USA
| | - George Korza
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, Connecticut, USA
| | - Peter Setlow
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, Connecticut, USA
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4
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Li J, Yang J, Xin W, Wu S, Wang X, Wang C, Zhang Z. Inactivation of Bacillus subtilis spores by a combination of high-pressure thermal treatment and potassium sorbate. Food Microbiol 2023; 115:104345. [PMID: 37567628 DOI: 10.1016/j.fm.2023.104345] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2022] [Revised: 06/21/2023] [Accepted: 07/23/2023] [Indexed: 08/13/2023]
Abstract
Combining High-pressure Thermal Treatment (HPTT) and Potassium Sorbate (PS) may have a stronger spore inactivation effect. Spores of Bacillus subtilis were subjected to HPTT at 600 MPa-65 °C/75 °C and a combination of HPTT and PS of 0.1% and 0.2% concentrations. After these treatments, different procedures and techniques were employed to investigate the spore's inactivation. The results revealed that 4.92 ± 0.05 log spores were inactivated after treatment at 600 MPa-75 °C, while 5.97 ± 0.09 log spores were inactivated when the HPTT treatment was combined with 0.2% PS. Changes in permeability of the spore's inner membrane were characterized by OD600 value and release rates of nucleic acids, protein, and dipicolinic acid (DPA). Compared with HPTT treatment at 600 MPa-75 °C, the OD600 value of spores decreased further by about 50% after treatment with a combination of HPTT and 0.2% PS. Additionally, the combined treatments resulted in a significant increase in the OD260 and OD280 values, as well as the DPA release. The spore size analysis indicated a significant decrease in the size of spores treated with a combination of HPTT at 600 MPa-75 °C and PS of 0.2% concentration. Furthermore, the flow cytometry analysis and confocal laser scanning microscopy (CLSM) analysis indicated that the inner membrane damage of spores was higher after combined treatments than that after HPTT treatment alone. A significant reduction was also found in the Na+/K+-ATPase activity after the combined treatments. Also, the FTIR analysis revealed that the combined treatments resulted in significant adverse changes in the spores' inner membrane, cell wall, cortex, and nucleic acid. Therefore, the combination of HPTT and PS has a stronger inactivation effect and can be suggested as a promising strategy for the inactivation of Bacillus subtilis spores.
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Affiliation(s)
- Jiajia Li
- College of Food Science and Engineering, Ningxia University, Yinchuan, 750021, PR China
| | - Jie Yang
- College of Food Science and Engineering, Ningxia University, Yinchuan, 750021, PR China
| | - Weishan Xin
- College of Food Science and Engineering, Ningxia University, Yinchuan, 750021, PR China
| | - Sirui Wu
- College of Food Science and Engineering, Ningxia University, Yinchuan, 750021, PR China
| | - Xujuan Wang
- College of Food Science and Engineering, Ningxia University, Yinchuan, 750021, PR China
| | - Chuanfa Wang
- College of Food Science and Engineering, Ningxia University, Yinchuan, 750021, PR China
| | - Zhong Zhang
- College of Food Science and Engineering, Ningxia University, Yinchuan, 750021, PR China.
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5
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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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6
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Yu B, Kanaan J, Shames H, Wicander J, Aryal M, Li Y, Korza G, Brul S, Kramer G, Li YQ, Nichols FC, Hao B, Setlow P. Identification and characterization of new proteins crucial for bacterial spore resistance and germination. Front Microbiol 2023; 14:1161604. [PMID: 37113233 PMCID: PMC10126465 DOI: 10.3389/fmicb.2023.1161604] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Accepted: 03/17/2023] [Indexed: 04/29/2023] Open
Abstract
2Duf, named after the presence of a transmembrane (TM) Duf421 domain and a small Duf1657 domain in its sequence, is likely located in the inner membrane (IM) of spores in some Bacillus species carrying a transposon with an operon termed spoVA 2mob. These spores are known for their extreme resistance to wet heat, and 2Duf is believed to be the primary contributor to this trait. In this study, we found that the absence of YetF or YdfS, both Duf421 domain-containing proteins and found only in wild-type (wt) B. subtilis spores with YetF more abundant, leads to decreased resistance to wet heat and agents that can damage spore core components. The IM phospholipid compositions and core water and calcium-dipicolinic acid levels of YetF-deficient spores are similar to those of wt spores, but the deficiency could be restored by ectopic insertion of yetF, and overexpression of YetF increased wt spore resistance to wet heat. In addition, yetF and ydfS spores have decreased germination rates as individuals and populations with germinant receptor-dependent germinants and increased sensitivity to wet heat during germination, potentially due to damage to IM proteins. These data are consistent with a model in which YetF, YdfS and their homologs modify IM structure to reduce IM permeability and stabilize IM proteins against wet heat damage. Multiple yetF homologs are also present in other spore forming Bacilli and Clostridia, and even some asporogenous Firmicutes, but fewer in asporogenous species. The crystal structure of a YetF tetramer lacking the TM helices has been reported and features two distinct globular subdomains in each monomer. Sequence alignment and structure prediction suggest this fold is likely shared by other Duf421-containing proteins, including 2Duf. We have also identified naturally occurring 2duf homologs in some Bacilli and Clostridia species and in wt Bacillus cereus spores, but not in wt B. subtilis. Notably, the genomic organization around the 2duf gene in most of these species is similar to that in spoVA 2mob, suggesting that one of these species was the source of the genes on this operon in the extremely wet heat resistant spore formers.
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Affiliation(s)
- Benjamin Yu
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
| | - Julia Kanaan
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
| | - Hannah Shames
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
| | - James Wicander
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
| | - Makunda Aryal
- Department of Physics, East Carolina University, Greenville, NC, United States
| | - Yunfeng Li
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
| | - George Korza
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
| | - Stanley Brul
- Molecular Biology and Microbial Food Safety, University of Amsterdam, Amsterdam, Netherlands
| | - Gertjan Kramer
- Laboratory for Mass Spectrometry of Biomolecules, Swammerdam Institute for Life Science, University of Amsterdam, Amsterdam, Netherlands
| | - Yong-qing Li
- Department of Physics, East Carolina University, Greenville, NC, United States
| | - Frank C. Nichols
- Division of Periodontology, UConn Health, Farmington, CT, United States
| | - Bing Hao
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
- Bing Hao,
| | - Peter Setlow
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
- *Correspondence: Peter Setlow,
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7
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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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8
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Biermann R, Niemeyer L, Rösner L, Ude C, Lindner P, Bice I, Beutel S. Facilitated endospore detection for
Bacillus
spp. through automated algorithm‐based image processing. Eng Life Sci 2021; 22:299-307. [PMID: 35382541 PMCID: PMC8961035 DOI: 10.1002/elsc.202100137] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 11/23/2021] [Accepted: 11/24/2021] [Indexed: 11/17/2022] Open
Abstract
Bacillus spp. endospores are important dormant cell forms and are distributed widely in environmental samples. While these endospores can have important industrial value (e.g. use in animal feed as probiotics), they can also be pathogenic for humans and animals, emphasizing the need for effective endospore detection. Standard spore detection by colony forming units (CFU) is time‐consuming, elaborate and prone to error. Manual spore detection by spore count in cell counting chambers via phase‐contrast microscopy is less time‐consuming. However, it requires a trained person to conduct. Thus, the development of a facilitated spore detection tool is necessary. This work presents two alternative quantification methods: first, a colorimetric assay for detecting the biomarker dipicolinic acid (DPA) adapted to modern needs and applied for Bacillus spp. and second, a model‐based automated spore detection algorithm for spore count in phase‐contrast microscopic pictures. This automated spore count tool advances manual spore detection in cell counting chambers, and does not require human overview after sample preparation. In conclusion, this developed model detected various Bacillus spp. endospores with a correctness of 85–89%, and allows an automation and time‐saving of Bacillus endospore detection. In the laboratory routine, endospore detection and counting was achieved within 5–10 min, compared to up to 48 h with conventional methods. The DPA‐assay on the other hand enabled very accurate spore detection by simple colorimetric measurement and can thus be applied as a reference method.
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Affiliation(s)
- Riekje Biermann
- Institute of Technical Chemistry Leibniz University Hannover Hannover Germany
| | - Laura Niemeyer
- Institute of Technical Chemistry Leibniz University Hannover Hannover Germany
| | - Laura Rösner
- Institute of Technical Chemistry Leibniz University Hannover Hannover Germany
| | - Christian Ude
- Institute of Technical Chemistry Leibniz University Hannover Hannover Germany
| | - Patrick Lindner
- Institute of Technical Chemistry Leibniz University Hannover Hannover Germany
| | - Ismet Bice
- Institute of Technical Chemistry Biochem Zusatzstoffe Handels‐ und Produktionsgesellschaft mbH Lohne Germany
| | - Sascha Beutel
- Institute of Technical Chemistry Leibniz University Hannover Hannover Germany
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9
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Lv R, Liu D, Zhou J. Bacterial spore inactivation by non-thermal technologies: resistance and inactivation mechanisms. Curr Opin Food Sci 2021. [DOI: 10.1016/j.cofs.2020.12.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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10
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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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11
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Liang D, Wang X, Wu X, Liao X, Chen F, Hu X. The effect of high pressure combined with moderate temperature and peptidoglycan fragments on spore inactivation. Food Res Int 2021; 148:110615. [PMID: 34507759 DOI: 10.1016/j.foodres.2021.110615] [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: 04/09/2021] [Revised: 07/15/2021] [Accepted: 07/19/2021] [Indexed: 11/26/2022]
Abstract
High pressure processing (HPP) is a promising non-thermal processing method for food production. However, extremely high pressure and temperature are often required to achieve spores inactivation and commercial sterilization using HPP. In this study, the combined treatment of HPP, moderate temperature, and peptidoglycan fragments (PGF) for spore inactivation was investigated. The combined treatment of 200 MPa and 1 mg/mL PGF at 80 °C for 20 min resulted in 8.6 log inactivation of Bacillus subtilis 168 and more than 5 log reductions of Clostridium sporogenes PA3679 spores, respectively. A strong synergistic effect on spore inactivation among HPP, PGF, and temperature was observed. By comparing the effect of the treatment on the fluidity of the inner membrane and structural change of spores using fluorescence assay, a probable inactivation mechanism was proposed. It was concluded that the spores were firstly triggered to enter the Stage I of the germination process by HPP and PGF, and then immediately inactivated by the mild heat. This novel processing method could be an alternative to ensure commercial sterilization in the food industry.
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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 100083, China; College of Food Science and Technology, Henan Agricultural University, Zhengzhou 450002, China
| | - Xu Wang
- College of Food Science, Northeast Agricultural University, Harbin 150030, China
| | - Xiaomeng Wu
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing 100083, China; Key Laboratory of Fruits and Vegetable Processing, Ministry of Agriculture, Beijing 100083, China
| | - Xiaojun Liao
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing 100083, China; Key Laboratory of Fruits and Vegetable Processing, Ministry of Agriculture, Beijing 100083, China
| | - Fang Chen
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing 100083, China; Key Laboratory of Fruits and Vegetable Processing, Ministry of Agriculture, Beijing 100083, China
| | - Xiaosong Hu
- College of Food Science and Nutritional Engineering, National Engineering Research Centre for Fruits and Vegetables Processing, China Agricultural University, Beijing 100083, China; Key Laboratory of Fruits and Vegetable Processing, Ministry of Agriculture, Beijing 100083, China.
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12
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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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13
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Aganovic K, Hertel C, Vogel RF, Johne R, Schlüter O, Schwarzenbolz U, Jäger H, Holzhauser T, Bergmair J, Roth A, Sevenich R, Bandick N, Kulling SE, Knorr D, Engel KH, Heinz V. Aspects of high hydrostatic pressure food processing: Perspectives on technology and food safety. Compr Rev Food Sci Food Saf 2021; 20:3225-3266. [PMID: 34056857 DOI: 10.1111/1541-4337.12763] [Citation(s) in RCA: 49] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 04/02/2021] [Accepted: 04/10/2021] [Indexed: 11/29/2022]
Abstract
The last two decades saw a steady increase of high hydrostatic pressure (HHP) used for treatment of foods. Although the science of biomaterials exposed to high pressure started more than a century ago, there still seem to be a number of unanswered questions regarding safety of foods processed using HHP. This review gives an overview on historical development and fundamental aspects of HHP, as well as on potential risks associated with HHP food applications based on available literature. Beside the combination of pressure and temperature, as major factors impacting inactivation of vegetative bacterial cells, bacterial endospores, viruses, and parasites, factors, such as food matrix, water content, presence of dissolved substances, and pH value, also have significant influence on their inactivation by pressure. As a result, pressure treatment of foods should be considered for specific food groups and in accordance with their specific chemical and physical properties. The pressure necessary for inactivation of viruses is in many instances slightly lower than that for vegetative bacterial cells; however, data for food relevant human virus types are missing due to the lack of methods for determining their infectivity. Parasites can be inactivated by comparatively lower pressure than vegetative bacterial cells. The degrees to which chemical reactions progress under pressure treatments are different to those of conventional thermal processes, for example, HHP leads to lower amounts of acrylamide and furan. Additionally, the formation of new unknown or unexpected substances has not yet been observed. To date, no safety-relevant chemical changes have been described for foods treated by HHP. Based on existing sensitization to non-HHP-treated food, the allergenic potential of HHP-treated food is more likely to be equivalent to untreated food. Initial findings on changes in packaging materials under HHP have not yet been adequately supported by scientific data.
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Affiliation(s)
- Kemal Aganovic
- DIL German Institute of Food Technologies e.V., Quakenbrück, Germany
| | - Christian Hertel
- DIL German Institute of Food Technologies e.V., Quakenbrück, Germany
| | - Rudi F Vogel
- Technical University of Munich (TUM), Munich, Germany
| | - Reimar Johne
- German Federal Institute for Risk Assessment (BfR), Berlin, Germany
| | - Oliver Schlüter
- Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB), Potsdam, Germany.,Alma Mater Studiorum, University of Bologna, Cesena, Italy
| | | | - Henry Jäger
- University of Natural Resources and Life Sciences (BOKU), Wien, Austria
| | - Thomas Holzhauser
- Division of Allergology, Paul-Ehrlich-Institut (PEI), Langen, Germany
| | | | - Angelika Roth
- Senate Commission on Food Safety (DFG), IfADo, Dortmund, Germany
| | - Robert Sevenich
- Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB), Potsdam, Germany.,Technical University of Berlin (TUB), Berlin, Germany
| | - Niels Bandick
- German Federal Institute for Risk Assessment (BfR), Berlin, Germany
| | | | | | | | - Volker Heinz
- DIL German Institute of Food Technologies e.V., Quakenbrück, Germany
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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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15
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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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16
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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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17
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Rao L, Feeherry FE, Ghosh S, Liao X, Lin X, Zhang P, Li Y, Doona CJ, Setlow P. Effects of lowering water activity by various humectants on germination of spores of Bacillus species with different germinants. Food Microbiol 2018; 72:112-127. [DOI: 10.1016/j.fm.2017.11.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Revised: 11/19/2017] [Accepted: 11/23/2017] [Indexed: 10/18/2022]
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18
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Sevenich R, Mathys A. Continuous Versus Discontinuous Ultra-High-Pressure Systems for Food Sterilization with Focus on Ultra-High-Pressure Homogenization and High-Pressure Thermal Sterilization: A Review. Compr Rev Food Sci Food Saf 2018; 17:646-662. [DOI: 10.1111/1541-4337.12348] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Accepted: 03/02/2018] [Indexed: 12/20/2022]
Affiliation(s)
- Robert Sevenich
- Dept. of Food Biotechnology and Food Process Engineering; Technische Univ. Berlin; Königin-Luise-Straße 22 Berlin D-14195 Germany
| | - Alexander Mathys
- ETH Zurich, Inst. of Food, Nutrition and Health; Laboratory of Sustainable Food Processing; Schmelzbergstrasse 9 Zurich CH-8092 Switzerland
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19
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Solyanikova IP, Suzina NE, Egozarian NS, Polivtseva VN, Prisyazhnaya NV, El-Registan GI, Mulyukin AL, Golovleva LA. The response of soil Arthrobacter agilis lush13 to changing conditions: Transition between vegetative and dormant state. JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH. PART. B, PESTICIDES, FOOD CONTAMINANTS, AND AGRICULTURAL WASTES 2017; 52:745-751. [PMID: 28976238 DOI: 10.1080/03601234.2017.1356665] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
This work was aimed at studying the response of soil non-spore-forming actinobacterial strain Arthrobacter agilis Lush 13 to changing natural conditions, such as nutrient availability and the presence of degradable and recalcitrant aliphatic and aromatic substrates. The A. agilis strain Lush13 was able to degrade octane, nonane, hexadecane, benzoate, phenol, and 2,3-, 2,4-, 2,5-, 2,6-dichlorophenols, but not grew on 3,4-dichlorophenol, 2,3,4-, 2,4,5-, 2,4,6-trichlorophenol (TCP), pentachlorophenol (PCP), 2-chlorobenzoate, 3-chlorobenzoate, 3,5-dichlorobenzoate, 2,4-dichlorobenzoate. Under growth-arresting conditions due to nitrogen- or multiple starvation or recalcitrant (non-utilizable) carbon source, the studied strain preserved viability for prolonged periods (4-24 months) due to transition to dormancy in the form of conglomerated small and ultrasmall cyst-like dormant cells (CLC). Dormant cells were shown to germinate rapidly (30 min or later) after removal of starvation stress, and this process was followed by breakdown of conglomerates with the eliberation and further division of small multiple actively growing daughter cells. Results of this study shed some light to adaptive capabilities of soil arthrobacters in pure and polluted environments.
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Affiliation(s)
- Inna P Solyanikova
- a G.K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences , Pushchino, Moscow Region , Russia
| | - Nataliya E Suzina
- a G.K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences , Pushchino, Moscow Region , Russia
| | - Nataliya S Egozarian
- a G.K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences , Pushchino, Moscow Region , Russia
- b M.V. Lomonosov Moscow State University , Faculty of Biotechnology , Russia
| | - Valentina N Polivtseva
- a G.K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences , Pushchino, Moscow Region , Russia
| | - Nataliya V Prisyazhnaya
- a G.K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences , Pushchino, Moscow Region , Russia
| | - Galina I El-Registan
- c S.N. Winogradsky Institute of Microbiology, Research Centre of Biotechnology, Russian Academy of Sciences , Moscow , Russia
| | - Andrey L Mulyukin
- c S.N. Winogradsky Institute of Microbiology, Research Centre of Biotechnology, Russian Academy of Sciences , Moscow , Russia
| | - Ludmila A Golovleva
- a G.K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences , Pushchino, Moscow Region , Russia
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20
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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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21
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Abstract
Dormant Bacillales and Clostridiales spores begin to grow when small molecules (germinants) trigger germination, potentially leading to food spoilage or disease. Germination-specific proteins sense germinants, transport small molecules, and hydrolyze specific bonds in cortex peptidoglycan and specific proteins. Major events in germination include (a) germinant sensing; (b) commitment to germinate; (c) release of spores' depot of dipicolinic acid (DPA); (d) hydrolysis of spores' peptidoglycan cortex; and (e) spore core swelling and water uptake, cell wall peptidoglycan remodeling, and restoration of core protein and inner spore membrane lipid mobility. Germination is similar between Bacillales and Clostridiales, but some species differ in how germinants are sensed and how cortex hydrolysis and DPA release are triggered. Despite detailed knowledge of the proteins and signal transduction pathways involved in germination, precisely what some germination proteins do and how they do it remain unclear.
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Affiliation(s)
- Peter Setlow
- Molecular Biology and Biophysics, UConn Health, Farmington, Connecticut 06030-3305;
| | - Shiwei Wang
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;
| | - Yong-Qing Li
- Department of Physics, East Carolina University, Greenville, North Carolina 27858-4353;
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22
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Trunet C, Carlin F, Coroller L. Investigating germination and outgrowth of bacterial spores at several scales. Trends Food Sci Technol 2017. [DOI: 10.1016/j.tifs.2017.03.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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23
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Walking dead: Permeabilization of heat-treated Geobacillus stearothermophilus ATCC 12980 spores under growth-preventing conditions. Food Microbiol 2017; 64:126-134. [DOI: 10.1016/j.fm.2016.12.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2016] [Revised: 12/19/2016] [Accepted: 12/19/2016] [Indexed: 11/20/2022]
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24
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Ha TMH, Yong D, Lee EMY, Kumar P, Lee YK, Zhou W. Activation and inactivation of Bacillus pumilus spores by kiloelectron volt X-ray irradiation. PLoS One 2017; 12:e0177571. [PMID: 28493969 PMCID: PMC5426783 DOI: 10.1371/journal.pone.0177571] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Accepted: 04/28/2017] [Indexed: 11/30/2022] Open
Abstract
In this study, we investigated the inactivation efficacy of endospore-forming bacteria, Bacillus pumilus, irradiated by low-energy X-rays of different beam qualities. The different low-energy X-rays studied had cut-off energies of 50, 100 and 150 keV. Bacillus pumilus spores (in biological indicator strips) were irradiated at step doses between 6.5 to 390 Gy. The resulting bacteria populations were then quantified by a pour plate method. Results showed that X-rays of lower energies were more effective in inactivating bacterial spores. In addition, an increment in bacterial population was observed at doses below 13Gy. We attributed this increase to a radiation-induced activation of bacterial spores. Four kinetic models were then evaluated for their prediction of bacterial spore behavior under irradiation. This included: (i) first-order kinetics model; (ii) Shull model; (iii) Sapru model; and (iv) probabilistic model. From R2 and AIC analyses, we noted that the probabilistic model performed the best, followed by the Sapru model. We highlighted that for simplicity in curve fitting the Sapru model should be used instead of the probabilistic model. A 12-log reduction in bacterial population (corresponding to a sterility assurance level of 10−6 as required in the sterilization of medical devices) was computed to be achievable at doses of 1000, 1600 and 2300 Gy for the three different X-ray cut-off energies respectively. These doses are an order in magnitude lesser than that required in gamma irradiation. This highlights the applicability of cheaper and safer table-top X-ray sources for sterilization application.
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Affiliation(s)
- Thi Mai Hoa Ha
- Singapore Institute of Manufacturing Technology, Singapore, Singapore
- * E-mail:
| | - Derrick Yong
- Singapore Institute of Manufacturing Technology, Singapore, Singapore
| | - Elizabeth Mei Yin Lee
- Singapore Institute of Manufacturing Technology, Singapore, Singapore
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore
| | - Prathab Kumar
- Food Science and Technology Programme, c/o Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Yuan Kun Lee
- Department of Microbiology, National University of Singapore, Singapore, Singapore
| | - Weibiao Zhou
- Food Science and Technology Programme, c/o Department of Chemistry, National University of Singapore, Singapore, Singapore
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25
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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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26
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Use of Raman Spectroscopy and Phase-Contrast Microscopy To Characterize Cold Atmospheric Plasma Inactivation of Individual Bacterial Spores. Appl Environ Microbiol 2016; 82:5775-84. [PMID: 27422840 DOI: 10.1128/aem.01669-16] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 07/13/2016] [Indexed: 12/22/2022] Open
Abstract
UNLABELLED Raman spectroscopy and phase-contrast microscopy were used to examine calcium dipicolinate (CaDPA) levels and rates of nutrient and nonnutrient germination of multiple individual Bacillus subtilis spores treated with cold atmospheric plasma (CAP). Major results for this work include the following: (i) >5 logs of spores deposited on glass surfaces were inactivated by CAP treatment for 3 min, while deposited spores placed inside an impermeable plastic bag were inactivated only ∼2 logs in 30 min; (ii) >80% of the spores treated for 1 to 3 min with CAP were nonculturable and retained CaDPA in their core, while >95% of spores treated with CAP for 5 to 10 min lost all CaDPA; (iii) Raman measurements of individual CAP-treated spores without CaDPA showed differences from spores that germinated with l-valine in terms of nucleic acids, lipids, and proteins; and (iv) 1 to 2 min of CAP treatment killed 99% of spores, but these spores still germinated with nutrients or exogenous CaDPA, albeit more slowly and to a lesser extent than untreated spores, while spores CAP treated for >3 min that retained CaDPA did not germinate via nutrients or CaDPA. However, even after 1 to 3 min of CAP treatment, spores germinated normally with dodecylamine. These results suggest that exposure to the present CAP configuration severely damages a spore's inner membrane and key germination proteins, such that the treated spores either lose CaDPA or can neither initiate nor complete germination with nutrients or CaDPA. Analysis of the various CAP components indicated that UV photons contributed minimally to spore inactivation, while charged particles and reactive oxygen species contributed significantly. IMPORTANCE Much research has shown that cold atmospheric plasma (CAP) is a promising tool for the inactivation of spores in the medical and food industries. However, knowledge about the effects of plasma treatment on spore properties is limited, especially at the single-cell level. In this study, Raman spectroscopy and phase-contrast microscopy were used to analyze CaDPA levels and kinetics of nutrient- and non-nutrient-germinant-induced germination of multiple individual spores of Bacillus subtilis that were treated by a planar CAP device. The roles of different plasma species involved in spore inactivation were also investigated. The knowledge obtained in this study will aid in understanding the mechanism(s) of spore inactivation by CAP and potentially facilitate the development of more effective and efficient plasma sterilization techniques in various applications.
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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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Chemical Kinetics for the Microbial Safety of Foods Treated with High Pressure Processing or Hurdles. FOOD ENGINEERING REVIEWS 2016. [DOI: 10.1007/s12393-015-9138-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Yan ZY, Ai XX, Su YL, Liu XY, Shan XH, Wu SM. Intracellular Biosynthesis of Fluorescent CdSe Quantum Dots in Bacillus subtilis: A Strategy to Construct Signaling Bacterial Probes for Visually Detecting Interaction Between Bacillus subtilis and Staphylococcus aureus. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2016; 22:13-21. [PMID: 26687198 DOI: 10.1017/s1431927615015548] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In this work, fluorescent Bacillus subtilis (B. subtilis) cells were developed as probes for imaging applications and to explore behaviorial interaction between B. subtilis and Staphylococcus aureus (S. aureus). A novel biological strategy of coupling intracellular biochemical reactions for controllable biosynthesis of CdSe quantum dots by living B. subtilis cells was demonstrated, through which highly luminant and photostable fluorescent B. subtilis cells were achieved with good uniformity. With the help of the obtained fluorescent B. subtilis cells probes, S. aureus cells responded to co-cultured B. subtilis and to aggregate. The degree of aggregation was calculated and nonlinearly fitted to a polynomial model. Systematic investigations of their interactions implied that B. subtilis cells inhibit the growth of neighboring S. aureus cells, and this inhibition was affected by both the growth stage and the amount of surrounding B. subtilis cells. Compared to traditional methods of studying bacterial interaction between two species, such as solid culture medium colony observation and imaging mass spectrometry detection, the procedures were more simple, vivid, and photostable due to the efficient fluorescence intralabeling with less influence on the cells' surface, which might provide a new paradigm for future visualization of microbial behavior.
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Affiliation(s)
- Zheng-Yu Yan
- 1Department of Analytical Chemistry,China Pharmaceutical University,24 Tongjia Lane,Gulou District,Nanjing 210009,China
| | - Xiao-Xia Ai
- 1Department of Analytical Chemistry,China Pharmaceutical University,24 Tongjia Lane,Gulou District,Nanjing 210009,China
| | - Yi-Long Su
- 1Department of Analytical Chemistry,China Pharmaceutical University,24 Tongjia Lane,Gulou District,Nanjing 210009,China
| | - Xin-Ying Liu
- 1Department of Analytical Chemistry,China Pharmaceutical University,24 Tongjia Lane,Gulou District,Nanjing 210009,China
| | - Xiao-Hui Shan
- 3Laizhou Entry-Exit Inspection and Quarantine Bureau,Laizhou 261400,China
| | - Sheng-Mei Wu
- 1Department of Analytical Chemistry,China Pharmaceutical University,24 Tongjia Lane,Gulou District,Nanjing 210009,China
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Inactivation of Bacillus amyloliquefaciens spores by continuous high-pressure-assisted thermal sterilization in an oil-in-water (o/w) emulsion with 10 % soybean oil. Eur Food Res Technol 2015. [DOI: 10.1007/s00217-015-2600-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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31
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Abstract
Bacterial spores, despite being metabolically dormant, possess the remarkable capacity to detect nutrients and other molecules in their environment through a biochemical sensory apparatus that can trigger spore germination, allowing the return to vegetative growth within minutes of exposure of germinants. We demonstrate here that bacterial spores of multiple species retain memory of transient exposures to germinant stimuli that can result in altered responses to subsequent exposure. The magnitude and decay of these memory effects depend on the pulse duration as well as on the separation time, incubation temperature, and pH values between the pulses. Spores of Bacillus species germinate in response to nutrients that interact with germinant receptors (GRs) in the spore’s inner membrane, with different nutrient types acting on different receptors. In our experiments, B. subtilis spores display memory when the first and second germinant pulses target different receptors, suggesting that some components of spore memory are downstream of GRs. Furthermore, nonnutrient germinants, which do not require GRs, exhibit memory either alone or in combination with nutrient germinants, and memory of nonnutrient stimulation is found to be more persistent than that induced by GR-dependent stimuli. Spores of B. cereus and Clostridium difficile also exhibit germination memory, suggesting that memory may be a general property of bacterial spores. These observations along with experiments involving strains with mutations in various germination proteins suggest a model in which memory is stored primarily in the metastable states of SpoVA proteins, which comprise a channel for release of dipicolinic acid, a major early event in spore germination. Cellular memory is defined as a sustained response to a transient environmental stimulus, and yet its generation and storage have not been described in bacterial spores. We demonstrate here that bacterial spores of multiple species retain memory of transient exposures to germinant stimuli that can result in altered responses to subsequent exposure. Memory was induced by activation of germinant receptors (GRs) or by GR-independent germinants and was accessed by both GR-dependent and GR-independent germinants. Analysis of effects on memory of exposure to GR-dependent and GR-independent germinants as well as in spores lacking various germination proteins suggests a model in which memory is stored primarily in metastable states of SpoVA proteins which comprise a channel for release of spore dipicolinic acid. Spore memory can also significantly reduce the concentration of nutrient germinants necessary to trigger germination, and this may be used to respond to low levels of nutrient germinants.
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Doona CJ, Feeherry FE, Kustin K, Olinger GG, Setlow P, Malkin AJ, Leighton T. Fighting Ebola with novel spore decontamination technologies for the military. Front Microbiol 2015; 6:663. [PMID: 26322021 PMCID: PMC4533522 DOI: 10.3389/fmicb.2015.00663] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 06/17/2015] [Indexed: 11/13/2022] Open
Abstract
Recently, global public health organizations such as Doctors without Borders (MSF), the World Health Organization (WHO), Public Health Canada, National Institutes of Health (NIH), and the U.S. government developed and deployed Field Decontamination Kits (FDKs), a novel, lightweight, compact, reusable decontamination technology to sterilize Ebola-contaminated medical devices at remote clinical sites lacking infra-structure in crisis-stricken regions of West Africa (medical waste materials are placed in bags and burned). The basis for effectuating sterilization with FDKs is chlorine dioxide (ClO2) produced from a patented invention developed by researchers at the US Army Natick Soldier RD&E Center (NSRDEC) and commercialized as a dry mixed-chemical for bacterial spore decontamination. In fact, the NSRDEC research scientists developed an ensemble of ClO2 technologies designed for different applications in decontaminating fresh produce; food contact and handling surfaces; personal protective equipment; textiles used in clothing, uniforms, tents, and shelters; graywater recycling; airplanes; surgical instruments; and hard surfaces in latrines, laundries, and deployable medical facilities. These examples demonstrate the far-reaching impact, adaptability, and versatility of these innovative technologies. We present herein the unique attributes of NSRDEC's novel decontamination technologies and a Case Study of the development of FDKs that were deployed in West Africa by international public health organizations to sterilize Ebola-contaminated medical equipment. FDKs use bacterial spores as indicators of sterility. We review the properties and structures of spores and the mechanisms of bacterial spore inactivation by ClO2. We also review mechanisms of bacterial spore inactivation by novel, emerging, and established non-thermal technologies for food preservation, such as high pressure processing, irradiation, cold plasma, and chemical sanitizers, using an array of Bacillus subtilis mutants to probe mechanisms of spore germination and inactivation. We employ techniques of high-resolution atomic force microscopy and phase contrast microscopy to examine the effects of γ-irradiation on bacterial spores of Bacillus anthracis, Bacillus thuringiensis, and Bacillus atrophaeus spp. and of ClO2 on B. subtilis spores, and present in detail assays using spore bio-indicators to ensure sterility when decontaminating with ClO2.
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Affiliation(s)
- Christopher J Doona
- U.S. Army Natick - Soldier RD&E Center, Warfighter Directorate, Natick, MA USA
| | - Florence E Feeherry
- U.S. Army Natick - Soldier RD&E Center, Warfighter Directorate, Natick, MA USA
| | - Kenneth Kustin
- Department of Chemistry, Emeritus, Brandeis University, Waltham, MA USA
| | - Gene G Olinger
- National Institute of Allergy and Infectious Diseases, Integrated Research Facility - Division of Clinical Research, Fort Detrick, MD USA
| | - Peter Setlow
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT USA
| | - Alexander J Malkin
- Biosciences and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA USA
| | - Terrance Leighton
- Children's Hospital - Oakland Research Institute, University of California San Francisco - Benioff, Oakland, CA USA
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High-precision fitting measurements of the kinetics of size changes during germination of individual Bacillus spores. Appl Environ Microbiol 2015; 80:4606-15. [PMID: 24837375 DOI: 10.1128/aem.01204-14] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
High-precision measurements of size changes of individual bacterial spores based on ellipse fitting to bright-field images recorded with a digital camera were employed to monitor the germination of Bacillus spores with a precision of ~5 nm. To characterize the germination of individual spores, we recorded bright-field and phase-contrast images and found that the timing of changes in their normalized intensities coincided, so the bright-field images can be used to characterize spore size and refractility changes during germination. The major conclusions from this work were as follows. (i) The sizes of germinating B. cereus spores were nearly unchanged until Trelease, the time of the completion of CaDPA (a 1:1 chelate of Ca(2+) and dipicolinic acid [DPA]) release after addition of nutrient germinants. (ii) The minor axis of germinating B. cereus spores rapidly increased by ~50 nm in a few seconds right after Trelease, while the major axis was slightly decreased or unchanged. Both the minor and major axes remained unchanged for a further 30 to 45 s and then increased by 100 to 200 nm by Tlys, the time of completion of cortex lysis. (iii) Individual spores in a population showed significant heterogeneity in the timing of germination events, such as Trelease and Tlys, but also variation in size changes during germination. (iv) Bacillus subtilis wild-type spores, B. subtilis spores lacking the cortex-lytic enzyme CwlJ, and wild-type Bacillus megaterium spores showed similar kinetics of size changes during nutrient germination. The size increases in germinating spores probably result from uptake of water and cortex lysis after completion of CaDPA release.
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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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Slow leakage of Ca-dipicolinic acid from individual bacillus spores during initiation of spore germination. J Bacteriol 2015; 197:1095-103. [PMID: 25583976 DOI: 10.1128/jb.02490-14] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
When exposed to nutrient or nonnutrient germinants, individual Bacillus spores can return to life through germination followed by outgrowth. Laser tweezers, Raman spectroscopy, and either differential interference contrast or phase-contrast microscopy were used to analyze the slow dipicolinic acid (DPA) leakage (normally ∼20% of spore DPA) from individual spores that takes place prior to the lag time, Tlag, when spores begin rapid release of remaining DPA. Major conclusions from this work with Bacillus subtilis spores were as follows: (i) slow DPA leakage from wild-type spores germinating with nutrients did not begin immediately after nutrient exposure but only at a later heterogeneous time T1; (ii) the period of slow DPA leakage (ΔTleakage = Tlag - T1) was heterogeneous among individual spores, although the amount of DPA released in this period was relatively constant; (iii) increases in germination temperature significantly decreased T1 times but increased values of ΔTleakage; (iv) upon germination with l-valine for 10 min followed by addition of d-alanine to block further germination, all germinated spores had T1 times of less than 10 min, suggesting that T1 is the time when spores become committed to germinate; (v) elevated levels of SpoVA proteins involved in DPA movement in spore germination decreased T1 and Tlag times but not the amount of DPA released in ΔTleakage; (vi) lack of the cortex-lytic enzyme CwlJ increased DPA leakage during germination due to longer ΔTleakage times in which more DPA was released; and (vii) there was slow DPA leakage early in germination of B. subtilis spores by the nonnutrients CaDPA and dodecylamine and in nutrient germination of Bacillus cereus and Bacillus megaterium spores. Overall, these findings have identified and characterized a new early event in Bacillus spore germination.
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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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Georget E, Miller B, Aganovic K, Callanan M, Heinz V, Mathys A. Bacterial spore inactivation by ultra-high pressure homogenization. INNOV FOOD SCI EMERG 2014. [DOI: 10.1016/j.ifset.2014.08.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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38
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Kinetic study of Bacillus cereus spore inactivation by high pressure high temperature treatment. INNOV FOOD SCI EMERG 2014. [DOI: 10.1016/j.ifset.2014.07.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Georget E, Miller B, Callanan M, Heinz V, Mathys A. (Ultra) high pressure homogenization for continuous high pressure sterilization of pumpable foods - a review. Front Nutr 2014; 1:15. [PMID: 25988118 PMCID: PMC4428391 DOI: 10.3389/fnut.2014.00015] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 08/01/2014] [Indexed: 11/29/2022] Open
Abstract
Bacterial spores have a strong resistance to both chemical and physical hurdles and create a risk for the food industry, which has been tackled by applying high thermal intensity treatments to sterilize food. These strong thermal treatments lead to a reduction of the organoleptic and nutritional properties of food and alternatives are actively searched for. Innovative hurdles offer an alternative to inactivate bacterial spores. In particular, recent technological developments have enabled a new generation of high pressure homogenizer working at pressures up to 400 MPa and thus, opening new opportunities for high pressure sterilization of foods. In this short review, we summarize the work conducted on (ultra) high pressure homogenization (U)HPH to inactivate endospores in model and food systems. Specific attention is given to process parameters (pressure, inlet, and valve temperatures). This review gathers the current state of the art and underlines the potential of UHPH sterilization of pumpable foods while highlighting the needs for future work.
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Affiliation(s)
- Erika Georget
- German Institute of Food Technologies (DIL), Quakenbrueck, Germany
- Institute of Food Chemistry, Leibniz University of Hanover, Hanover, Germany
| | - Brittany Miller
- German Institute of Food Technologies (DIL), Quakenbrueck, Germany
| | | | - Volker Heinz
- German Institute of Food Technologies (DIL), Quakenbrueck, Germany
| | - Alexander Mathys
- German Institute of Food Technologies (DIL), Quakenbrueck, Germany
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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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Monitoring of commitment, blocking, and continuation of nutrient germination of individual Bacillus subtilis spores. J Bacteriol 2014; 196:2443-54. [PMID: 24769693 DOI: 10.1128/jb.01687-14] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Short exposures of Bacillus spores to nutrient germinants can commit spores to germinate when germinants are removed or their binding to the spores' nutrient germinant receptors (GRs) is inhibited. Bacillus subtilis spores were exposed to germinants for various periods, followed by germinant removal to prevent further commitment. Release of spore dipicolinic acid (DPA) was then measured by differential interference contrast microscopy to monitor germination of multiple individual spores, and spores did not release DPA after 1 to 2 min of germinant exposure until ~7 min after germinant removal. With longer germinant exposures, percentages of committed spores with times for completion of DPA release (Trelease) greater than the time of germinant removal (Tb) increased, while the time Tlag - Tb, where Tlag represents the time when rapid DPA release began, was decreased but rapid DPA release times (ΔTrelease = Trelease - Tlag) were increased; Factors affecting average Trelease values and the percentages of committed spores were germinant exposure time, germinant concentration, sporulation conditions, and spore heat activation, as previously shown for commitment of spore populations. Surprisingly, germination of spores given a 2nd short germinant exposure 30 to 45 min after a 1st exposure of the same duration was significantly higher than after the 1st exposure, but the number of spores that germinated in the 2nd germinant exposure decreased as the interval between germinant exposures increased up to 12 h. The latter results indicate that spores have some memory, albeit transient, of their previous exposure to nutrient germinants.
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Analysis of the loss in heat and acid resistance during germination of spores of Bacillus species. J Bacteriol 2014; 196:1733-40. [PMID: 24563034 DOI: 10.1128/jb.01555-14] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A major event in the nutrient germination of spores of Bacillus species is release of the spores' large depot of dipicolinic acid (DPA). This event is preceded by both commitment, in which spores continue through germination even if germinants are removed, and loss of spore heat resistance. The latter event is puzzling, since spore heat resistance is due largely to core water content, which does not change until DPA is released during germination. We now find that for spores of two Bacillus species, the early loss in heat resistance during germination is most likely due to release of committed spores' DPA at temperatures not lethal for dormant spores. Loss in spore acid resistance during germination also paralleled commitment and was also associated with the release of DPA from committed spores at acid concentrations not lethal for dormant spores. These observations plus previous findings that DPA release during germination is preceded by a significant release of spore core cations suggest that there is a significant change in spore inner membrane permeability at commitment. Presumably, this altered membrane cannot retain DPA during heat or acid treatments innocuous for dormant spores, resulting in DPA-less spores that are rapidly killed.
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Abstract
Spores of Bacillus species can remain in their dormant and resistant states for years, but exposure to agents such as specific nutrients can cause spores' return to life within minutes in the process of germination. This process requires a number of spore-specific proteins, most of which are in or associated with the inner spore membrane (IM). These proteins include the (i) germinant receptors (GRs) that respond to nutrient germinants, (ii) GerD protein, which is essential for GR-dependent germination, (iii) SpoVA proteins that form a channel in spores' IM through which the spore core's huge depot of dipicolinic acid is released during germination, and (iv) cortex-lytic enzymes (CLEs) that degrade the large peptidoglycan cortex layer, allowing the spore core to take up much water and swell, thus completing spore germination. While much has been learned about nutrient germination, major questions remain unanswered, including the following. (i) How do nutrient germinants penetrate through spores' outer layers to access GRs in the IM? (ii) What happens during the highly variable and often long lag period between the exposure of spores to nutrient germinants and the commitment of spores to germinate? (iii) What do GRs and GerD do, and how do these proteins interact? (iv) What is the structure of the SpoVA channel in spores' IM, and how is this channel gated? (v) What is the precise state of the spore IM, which has a number of novel properties even though its lipid composition is very similar to that of growing cells? (vi) How is CLE activity regulated such that these enzymes act only when germination has been initiated? (vii) And finally, how does the germination of spores of clostridia compare with that of spores of bacilli?
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