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Battling S, Engel T, Herweg E, Niehoff PJ, Pesch M, Scholand T, Schöpping M, Sonntag N, Büchs J. Highly efficient fermentation of 5-keto-D-fructose with Gluconobacter oxydans at different scales. Microb Cell Fact 2022; 21:255. [PMID: 36496372 PMCID: PMC9741787 DOI: 10.1186/s12934-022-01980-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Accepted: 11/30/2022] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND The global market for sweeteners is increasing, and the food industry is constantly looking for new low-caloric sweeteners. The natural sweetener 5-keto-D-fructose is one such candidate. 5-Keto-D-fructose has a similar sweet taste quality as fructose. Developing a highly efficient 5-keto-D-fructose production process is key to being competitive with established sweeteners. Hence, the 5-keto-D-fructose production process was optimised regarding titre, yield, and productivity. RESULTS For production of 5-keto-D-fructose with G. oxydans 621H ΔhsdR pBBR1-p264-fdhSCL-ST an extended-batch fermentation was conducted. During fructose feeding, a decreasing respiratory activity occurred, despite sufficient carbon supply. Oxygen and second substrate limitation could be excluded as reasons for the decreasing respiration. It was demonstrated that a short period of oxygen limitation has no significant influence on 5-keto-D-fructose production, showing the robustness of this process. Increasing the medium concentration increased initial biomass formation. Applying a fructose feeding solution with a concentration of approx. 1200 g/L, a titre of 545 g/L 5-keto-D-fructose was reached. The yield was with 0.98 g5-keto-d-fructose/gfructose close to the theoretical maximum. A 1200 g/L fructose solution has a viscosity of 450 mPa∙s at a temperature of 55 °C. Hence, the solution itself and the whole peripheral feeding system need to be heated, to apply such a highly concentrated feeding solution. Thermal treatment of highly concentrated fructose solutions led to the formation of 5-hydroxymethylfurfural, which inhibited the 5-keto-D-fructose production. Therefore, fructose solutions were only heated to about 100 °C for approx. 10 min. An alternative feeding strategy was investigated using solid fructose cubes, reaching the highest productivities above 10 g5-keto-d-fructose/L/h during feeding. Moreover, the scale-up of the 5-keto-D-fructose production to a 150 L pressurised fermenter was successfully demonstrated using liquid fructose solutions (745 g/L). CONCLUSION We optimised the 5-keto-D-fructose production process and successfully increased titre, yield and productivity. By using solid fructose, we presented a second feeding strategy, which can be of great interest for further scale-up experiments. A first scale-up of this process was performed, showing the possibility for an industrial production of 5-keto-D-fructose.
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Affiliation(s)
- Svenja Battling
- grid.1957.a0000 0001 0728 696XAVT-Chair for Biochemical Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany
| | - Tobias Engel
- grid.1957.a0000 0001 0728 696XAVT-Chair for Biochemical Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany
| | - Elena Herweg
- grid.1957.a0000 0001 0728 696XAVT-Chair for Biochemical Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany
| | - Paul-Joachim Niehoff
- grid.1957.a0000 0001 0728 696XAVT-Chair for Biochemical Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany
| | - Matthias Pesch
- grid.1957.a0000 0001 0728 696XAVT-Chair for Biochemical Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany
| | - Theresa Scholand
- grid.1957.a0000 0001 0728 696XAVT-Chair for Biochemical Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany
| | - Marie Schöpping
- grid.1957.a0000 0001 0728 696XAVT-Chair for Biochemical Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany
| | - Nina Sonntag
- grid.1957.a0000 0001 0728 696XAVT-Chair for Biochemical Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany
| | - Jochen Büchs
- grid.1957.a0000 0001 0728 696XAVT-Chair for Biochemical Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany
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Recovery of Salts from Synthetic Erythritol Culture Broth via Electrodialysis: An Alternative Strategy from the Bin to the Loop. SUSTAINABILITY 2022. [DOI: 10.3390/su14020734] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Sustainability and circularity are currently two relevant drivers in the development and optimisation of industrial processes. This study assessed the use of electrodialysis (ED) to purify synthetic erythritol culture broth and for the recovery of the salts in solution, for minimising the generation of waste by representing an efficient alternative to remove ions, ensuring their recovery process contributing to reaching cleaner standards in erythritol production. Removal and recovery of ions was evaluated for synthetic erythritol culture broth at three different levels of complexity using a stepwise voltage in the experimental settings. ED was demonstrated to be a potential technology removing between 91.7–99.0% of ions from the synthetic culture broth, with 49–54% current efficiency. Besides this, further recovery of ions into the concentrated fraction was accomplished. The anions and cations were recovered in a second fraction reaching concentration factors between 1.5 to 2.5 times while observing low level of erythritol losses (<2%), with an energy consumption of 4.10 kWh/m3.
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Mladenović KG, Grujović MŽ, Kiš M, Furmeg S, Tkalec VJ, Stefanović OD, Kocić-Tanackov SD. Enterobacteriaceae in food safety with an emphasis on raw milk and meat. Appl Microbiol Biotechnol 2021; 105:8615-8627. [PMID: 34731280 DOI: 10.1007/s00253-021-11655-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 10/18/2021] [Accepted: 10/19/2021] [Indexed: 10/19/2022]
Abstract
There has been a growing interest in traditional dairy (such as raw milk cheeses) and meat products, in recent years. However, these products are suitable and nutrient medium and may be easily contaminated by microorganisms such as Enterobacteriaceae. Enterobacteriaceae are considered to be the indicator bacteria for microbiological quality of food and hygiene status of a production process. Additionally, the food contaminated by Enterobacteriaceae poses a microbiological risk for consumers. In fact, the contamination of raw milk and meat by Enterobacteriaceae amid manufacturing may easily occur from various environmental sources, and this group of bacteria is frequently detected in dairy and meat products. Therefore, monitoring the microbiological quality of the used raw material and maintaining high standards of hygiene in the production process are mandatory for a high quality of traditional products and the safety of the potential consumers. The goal of this review is to present the most recent survey on Enterobacteriaceae growth, number, and distribution in raw milk cheeses and meat, as well as to discuss the sources of contamination and methods of control. KEY POINTS: • Enterobacteriaceae: role and importance in milk and meat products, EU legal regulations • Dynamics, distribution, and survival of Enterobacteriaceae in milk and meat • Mechanisms of control of Enterobacteriaceae in dairy products.
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Affiliation(s)
- K G Mladenović
- Faculty of Science, Department of Biology and Ecology, University of Kragujevac, Radoja Domanovića 12, 34000, Kragujevac, Republic of Serbia. .,Institute for Information Technologies, Department of Science, University of Kragujevac, JovanaCvijica Bb, 34000, Kragujevac, Republic of Serbia.
| | - M Ž Grujović
- Faculty of Science, Department of Biology and Ecology, University of Kragujevac, Radoja Domanovića 12, 34000, Kragujevac, Republic of Serbia.,Institute for Information Technologies, Department of Science, University of Kragujevac, JovanaCvijica Bb, 34000, Kragujevac, Republic of Serbia
| | - M Kiš
- Laboratory for Food and Feed Microbiology, Croatian Veterinary Institute, Veterinary Institute Križevci, Zakmardijeva 10, 48260, Križevci, Croatia
| | - S Furmeg
- Laboratory for Food and Feed Microbiology, Croatian Veterinary Institute, Veterinary Institute Križevci, Zakmardijeva 10, 48260, Križevci, Croatia
| | - V Jaki Tkalec
- Laboratory for Food and Feed Microbiology, Croatian Veterinary Institute, Veterinary Institute Križevci, Zakmardijeva 10, 48260, Križevci, Croatia
| | - O D Stefanović
- Faculty of Science, Department of Biology and Ecology, University of Kragujevac, Radoja Domanovića 12, 34000, Kragujevac, Republic of Serbia
| | - S D Kocić-Tanackov
- Faculty of Technology, University in Novi Sad, Cara Lazara 1, 21000, Novi Sad, Republic of Serbia
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4
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Martin G, Sharma S, Ryan W, Srinivasan NK, Senko JM. Identification of Microbiological Activities in Wet Flue Gas Desulfurization Systems. Front Microbiol 2021; 12:675628. [PMID: 34262541 PMCID: PMC8273512 DOI: 10.3389/fmicb.2021.675628] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Accepted: 06/07/2021] [Indexed: 11/18/2022] Open
Abstract
Thermoelectric power generation from coal requires large amounts of water, much of which is used for wet flue gas desulfurization (wFGD) systems that minimize sulfur emissions, and consequently, acid rain. The microbial communities in wFGDs and throughout thermoelectric power plants can influence system performance, waste processing, and the long term stewardship of residual wastes. Any microorganisms that survive in wFGD slurries must tolerate high total dissolved solids concentrations (TDS) and temperatures (50–60°C), but the inocula for wFGDs are typically from fresh surface waters (e.g., lakes or rivers) of low TDS and temperatures, and whose activity might be limited under the physicochemically extreme conditions of the wFGD. To determine the extents of microbiological activities in wFGDs, we examined the microbial activities and communities associated with three wFGDs. O2 consumption rates of three wFGD slurries were optimal at 55°C, and living cells could be detected microscopically, indicating that living and active communities of organisms were present in the wFGD and could metabolize at the high temperature of the wFGD. A 16S rRNA gene-based survey revealed that the wFGD-associated microbial communities included taxa attributable to both thermophilic and mesophilic lineages. Metatranscriptomic analysis of one of the wFGDs indicated an abundance of active Burholderiaceae and several Gammaproteobacteria, and production of transcripts associated with carbohydrate metabolism, osmotic stress response, as well as phage, prophages, and transposable elements. These results illustrate that microbial activities can be sustained in physicochemically extreme wFGDs, and these activities may influence the performance and environmental impacts of thermoelectric power plants.
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Affiliation(s)
- Gregory Martin
- Department of Biology, The University of Akron, Akron, OH, United States
| | - Shagun Sharma
- Department of Biology, The University of Akron, Akron, OH, United States.,Integrated Bioscience Program, The University of Akron, Akron, OH, United States
| | - William Ryan
- Department of Biology, The University of Akron, Akron, OH, United States
| | | | - John M Senko
- Department of Biology, The University of Akron, Akron, OH, United States.,Integrated Bioscience Program, The University of Akron, Akron, OH, United States.,Department of Geosciences, The University of Akron, Akron, OH, United States
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Siderakou D, Zilelidou E, Poimenidou S, Tsipra I, Ouranou E, Papadimitriou K, Skandamis P. Assessing the survival and sublethal injury kinetics of Listeria monocytogenes under different food processing-related stresses. Int J Food Microbiol 2021; 346:109159. [PMID: 33773356 DOI: 10.1016/j.ijfoodmicro.2021.109159] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2020] [Revised: 02/04/2021] [Accepted: 03/06/2021] [Indexed: 12/22/2022]
Abstract
The foodborne pathogen L. monocytogenes can be present in food processing environments where it is exposed to various stressors. These antimicrobial factors, which aim to eliminate the pathogen, can induce sub-lethal injury to the bacterial cells. In the present study, we investigated the efficacy of different treatments (stresses) relevant to food processing and preservation as well as sanitation methods, in generating sub-lethal injury at 4 °C and 20 °C to two L. monocytogenes strains, ScottA and EGDe. Additionally, we evaluated the survival and extent of L. monocytogenes injury after exposure to commonly used disinfectants (peracetic acid and benzalkonium chloride), following habituation in nutrient-deprived, high-salinity medium. Each stress had a different impact on the survival and injury kinetics of L. monocytogenes. The highest injury levels were caused by peracetic acid which, at 4 °C, generated high populations of injured cells without loss of viability. Other injury-inducing stresses were lactic acid and heating. Long-term habituation in nutrient-limited and high salinity medium (4 °C) and subsequent exposure to disinfectants resulted in higher survival and injury in benzalkonium chloride and increased survival, yet with lower injury levels, in peracetic acid at 20 °C. Taken together, these results highlight the potential food safety risk emerging from the occurrence of injured cells by commonly used food processing methods. Consequently, in order to accurately assess the impact of an antimicrobial method, its potential of inducing sublethal injury needs to be considered along with lethality.
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Affiliation(s)
- Danae Siderakou
- Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece
| | - Evangelia Zilelidou
- Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece
| | - Sofia Poimenidou
- Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece
| | - Ioanna Tsipra
- Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece
| | - Eleni Ouranou
- Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece
| | - Konstantinos Papadimitriou
- Department of Food Science and Technology, University of Peloponnese, Antikalamos, 24100 Kalamata, Greece
| | - Panagiotis Skandamis
- Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece.
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Michl TD, Hibbs B, Hyde L, Postma A, Tran DTT, Zhalgasbaikyzy A, Vasilev K, Meagher L, Griesser HJ, Locock KES. Bacterial membrane permeability of antimicrobial polymethacrylates: Evidence for a complex mechanism from super-resolution fluorescence imaging. Acta Biomater 2020; 108:168-177. [PMID: 32179195 DOI: 10.1016/j.actbio.2020.03.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 03/03/2020] [Accepted: 03/04/2020] [Indexed: 12/31/2022]
Abstract
Amphiphilic polymers bearing cationic moieties are an emerging alternative to traditional antibiotics given their broad-spectrum activity and low susceptibility to the development of resistance. To date, however, much remains unclear regarding their mechanism of action. Using functional assays (ATP leakage, cell viability, DNA binding) and super-high resolution structured illumination microscopy (OMX-SR) of fluorescently tagged polymers, we present evidence for a complex mechanism, involving membrane permeation as well as cellular uptake, interaction with intracellular targets and possible complexation with bacterial DNA. STATEMENT OF SIGNIFICANCE: This manuscript details the first study to systematically and directly investigate the mechanism of action of antimicrobial polymers, using super-resolution fluorescence imaging as well as functional assays. While many in the field cite membrane permeation as the sole mechanism underlying the activity of such polymers, we present evidence for multimodal actions including high cellular uptake and interaction with intracellular targets. It is also the first report to show competitive binding of antimicrobial polymers with bacterial DNA in a dose-dependent manner.
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Affiliation(s)
- Thomas D Michl
- School of Engineering, University of South Australia, Mawson Lakes Blvd, Mawson Lakes, SA 5095, Australia
| | - Ben Hibbs
- Materials Characterisation and Fabrication Platform, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Lauren Hyde
- Materials Characterisation and Fabrication Platform, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Almar Postma
- CSIRO Manufacturing, Research Way, Clayton, VIC 3168, Australia
| | - Dung Thuy Thi Tran
- School of Engineering, University of South Australia, Mawson Lakes Blvd, Mawson Lakes, SA 5095, Australia
| | - Aigerim Zhalgasbaikyzy
- School of Engineering, University of South Australia, Mawson Lakes Blvd, Mawson Lakes, SA 5095, Australia
| | - Krasimir Vasilev
- School of Engineering, University of South Australia, Mawson Lakes Blvd, Mawson Lakes, SA 5095, Australia
| | - Laurence Meagher
- Department of Materials Science and Engineering, Monash University, Clayton, VIC 3168, Australia
| | - Hans J Griesser
- Future Industries Institute, University of South Australia, Mawson Lakes Blvd, Mawson Lakes, SA 5095, Australia
| | - Katherine E S Locock
- CSIRO Manufacturing, Research Way, Clayton, VIC 3168, Australia; Department of Chemical Engineering, The University of Melbourne, Parkville, VIC 3010, Australia.
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Antimicrobial Air Filters Using Natural Sea Salt Particles for Deactivating Airborne Bacterial Particles. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2019; 17:ijerph17010190. [PMID: 31892112 PMCID: PMC6981996 DOI: 10.3390/ijerph17010190] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 12/18/2019] [Accepted: 12/22/2019] [Indexed: 11/17/2022]
Abstract
We developed an antimicrobial air filter using natural sea salt (NSS) particles. Airborne NSS particles were produced via an aerosol process and were continuously coated onto the surface of an air filter under various deposition times. The filtration efficiency and bactericidal performance of the NSS-coated filter against aerosolized bacterial particles (Staphylococcus epidermidis, Escherichia coli) were evaluated quantitatively. The filtration efficiency of the tested filter ranged from 95% to 99% depending on the deposition time, and the bactericidal performance demonstrated efficiencies of more than 98% against both tested bacterial bioaerosols when the NSS deposition ratio was more than 500 μg/cm2. The experimental results indicated that the NSS-coated filters have the potential to be used as effective antimicrobial air filters for decreasing environmental exposure to microbial contaminants.
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Wijnker JJ, Janssen PMW, Cebeci S, Koerten KV, Bekker M. Validation of a High-Throughput Sausage Casing Model for the Assessment of Bacterial Inactivation Affected by Salt Concentration, pH, and Temperature. J Food Prot 2019; 82:1769-1774. [PMID: 31538830 DOI: 10.4315/0362-028x.jfp-19-197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Previous studies have shown the efficacy of high concentrations of salt as the main preservative against vegetative bacteria present on natural sausage casings. These studies were limited in the number of variables and the interactions between these variables that were assessed. To remedy this situation, a MicroCasing high-throughput model was developed and validated to study the inactivation kinetics of various combinations of parameters (salt concentration, pH, and temperature) on eight bacterial isolates of Salmonella enterica, Staphylococcus aureus, Escherichia coli, and Listeria monocytogenes over a prolonged period. A Weibullian power model was the best fit to show the trends in sensitivity of each bacterial isolate to salt, pH, and temperature over time. The inactivation kinetics generated with this novel approach could serve as a predictive model for the required salting period for casings. The actual bacterial contamination of the product can vary with the respective production step during processing from animal intestine into sausage casings (initial level, ∼105 CFU/g; level after salting, <102 CFU/g). Subsequent selection and grading of these casings will require complete removal of all salt, and upon completion of this production step, the casings will be resalted. By determining the actual contamination level before the salting process, the minimum storage period in salt can be calculated and potentially optimized by adjusting the pH and temperature. As a result, a standard holding period of at least 30 days may no longer be necessary to produce salted natural casings in accordance with validated quality and food safety criteria.
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Affiliation(s)
- Joris J Wijnker
- Institute for Risk Assessment Sciences, Faculty of Veterinary Medicine, P.O. Box 80.175, NL-3508 TD, Utrecht University, Utrecht, The Netherlands
| | | | - Sabri Cebeci
- NIZO Food Research BV, P.O. Box 20, 6710 BA, Ede, The Netherlands
| | | | - Martijn Bekker
- NIZO Food Research BV, P.O. Box 20, 6710 BA, Ede, The Netherlands
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Kitichalermkiat A, Kurahachi M, Nonaka A, Nakayama M, Shimatani K, Shigemune N, Tsugukuni T, Hitomi J, Sato J, Sonoda T, Masuda Y, Honjoh KI, Miyamoto T. Effects of Epigallocatechin Gallate on Viability and Cellular Proteins of Staphylococcus aureus. FOOD SCIENCE AND TECHNOLOGY RESEARCH 2019. [DOI: 10.3136/fstr.25.277] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Apisada Kitichalermkiat
- Division of Food Science and Biotechnology, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University
| | - Masahiro Kurahachi
- Division of Food Science and Biotechnology, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University
| | - Ai Nonaka
- Division of Food Science and Biotechnology, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University
| | | | | | | | | | - Jun Hitomi
- Safety Science Research, R&D, Kao Corporation
| | - Jun Sato
- Safety Science Research, R&D, Kao Corporation
| | | | - Yoshimitsu Masuda
- Division of Food Science and Biotechnology, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University
| | - Ken-ichi Honjoh
- Division of Food Science and Biotechnology, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University
| | - Takahisa Miyamoto
- Division of Food Science and Biotechnology, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University
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Moura J, Freitas T, Cruz R, Pereira R, Silva A, Santos A, da Silva J, Luz-Lima C, Coutinho H. Antibacterial properties and modulation analysis of antibiotic activity of NaCe(MoO4)2 microcrystals. Microb Pathog 2019; 126:258-262. [DOI: 10.1016/j.micpath.2018.11.019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Accepted: 11/12/2018] [Indexed: 11/16/2022]
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Kim NH, Cho TJ, Rhee MS. Sodium Chloride Does Not Ensure Microbiological Safety of Foods: Cases and Solutions. ADVANCES IN APPLIED MICROBIOLOGY 2017; 101:1-47. [PMID: 29050664 DOI: 10.1016/bs.aambs.2017.05.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Addition of salt or salt-containing water to food is one of the oldest and most effective preservation methods in history; indeed, salt-cured foods are generally recognized as microbiologically safe due to their high salinity. However, a number of microbiological risks remain. The microbiological hazards and risks associated with salt-cured foods must be addressed more in-depth as they are likely to be underestimated by previous studies. This review examined a number of scientific reports and articles about the microbiological safety of salt-cured foods, which included salted, brined, pickled, and/or marinated vegetables, meat, and seafood. The following subjects are covered in order: (1) clinical cases and outbreaks attributed to salt-cured foods; (2) the prevalence of foodborne pathogens in such foods; (3) the molecular, physiological, and virulent responses of the pathogens to the presence of NaCl in both laboratory media and food matrices; (4) the survival and fate of microorganisms in salt-cured foods (in the presence/absence of additional processes); and (5) the interaction between NaCl and other stressors in food processes (e.g., acidification, antimicrobials, drying, and heating). The review provides a comprehensive overview of potentially hazardous pathogens associated with salt-cured foods and suggests further research into effective intervention techniques that will reduce their levels in the food chain.
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Affiliation(s)
- Nam Hee Kim
- Department of Biotechnology, Korea University, Seoul, Republic of Korea
| | - Tae Jin Cho
- Department of Biotechnology, Korea University, Seoul, Republic of Korea
| | - Min Suk Rhee
- Department of Biotechnology, Korea University, Seoul, Republic of Korea
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12
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Sultana ST, Call DR, Beyenal H. Maltodextrin enhances biofilm elimination by electrochemical scaffold. Sci Rep 2016; 6:36003. [PMID: 27782161 PMCID: PMC5080540 DOI: 10.1038/srep36003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Accepted: 09/22/2016] [Indexed: 01/08/2023] Open
Abstract
Electrochemical scaffolds (e-scaffolds) continuously generate low concentrations of H2O2 suitable for damaging wound biofilms without damaging host tissue. Nevertheless, retarded diffusion combined with H2O2 degradation can limit the efficacy of this potentially important clinical tool. H2O2 diffusion into biofilms and bacterial cells can be increased by damaging the biofilm structure or by activating membrane transportation channels by exposure to hyperosmotic agents. We hypothesized that e-scaffolds would be more effective against Acinetobacter baumannii and Staphylococcus aureus biofilms in the presence of a hyperosmotic agent. E-scaffolds polarized at -600 mVAg/AgCl were overlaid onto preformed biofilms in media containing various maltodextrin concentrations. E-scaffold alone decreased A. baumannii and S. aureus biofilm cell densities by (3.92 ± 0.15) log and (2.31 ± 0.12) log, respectively. Compared to untreated biofilms, the efficacy of the e-scaffold increased to a maximum (8.27 ± 0.05) log reduction in A. baumannii and (4.71 ± 0.12) log reduction in S. aureus biofilm cell densities upon 10 mM and 30 mM maltodextrin addition, respectively. Overall ~55% decrease in relative biofilm surface coverage was achieved for both species. We conclude that combined treatment with electrochemically generated H2O2 from an e-scaffold and maltodextrin is more effective in decreasing viable biofilm cell density.
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Affiliation(s)
- Sujala T. Sultana
- School of Chemical Engineering & Bioengineering, Washington State University, Pullman, 99164, WA, USA
| | - Douglas R. Call
- Paul G. Allen School for Global Animal Health, Washington State University, Pullman, 99164, WA, USA
| | - Haluk Beyenal
- School of Chemical Engineering & Bioengineering, Washington State University, Pullman, 99164, WA, USA
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Moscoso JA, Schramke H, Zhang Y, Tosi T, Dehbi A, Jung K, Gründling A. Binding of Cyclic Di-AMP to the Staphylococcus aureus Sensor Kinase KdpD Occurs via the Universal Stress Protein Domain and Downregulates the Expression of the Kdp Potassium Transporter. J Bacteriol 2016; 198:98-110. [PMID: 26195599 PMCID: PMC4686210 DOI: 10.1128/jb.00480-15] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2015] [Accepted: 07/14/2015] [Indexed: 02/06/2023] Open
Abstract
UNLABELLED Nucleotide signaling molecules are important intracellular messengers that regulate a wide range of biological functions. The human pathogen Staphylococcus aureus produces the signaling nucleotide cyclic di-AMP (c-di-AMP). This molecule is common among Gram-positive bacteria and in many organisms is essential for survival under standard laboratory growth conditions. In this study, we investigated the interaction of c-di-AMP with the S. aureus KdpD protein. The sensor kinase KdpD forms a two-component signaling system with the response regulator KdpE and regulates the expression of the kdpDE genes and the kdpFABC operon coding for the Kdp potassium transporter components. Here we show that the S. aureus KdpD protein binds c-di-AMP specifically and with an affinity in the micromolar range through its universal stress protein (USP) domain. This domain is located within the N-terminal cytoplasmic region of KdpD, and amino acids of a conserved SXS-X20-FTAXY motif are important for this binding. We further show that KdpD2, a second KdpD protein found in some S. aureus strains, also binds c-di-AMP, and our bioinformatics analysis indicates that a subclass of KdpD proteins in c-di-AMP-producing bacteria has evolved to bind this signaling nucleotide. Finally, we show that c-di-AMP binding to KdpD inhibits the upregulation of the kdpFABC operon under salt stress, thus indicating that c-di-AMP is a negative regulator of potassium uptake in S. aureus. IMPORTANCE Staphylococcus aureus is an important human pathogen and a major cause of food poisoning in Western countries. A common method for food preservation is the use of salt to drive dehydration. This study sheds light on the regulation of potassium uptake in Staphylococcus aureus, an important aspect of this bacterium's ability to tolerate high levels of salt. We show that the signaling nucleotide c-di-AMP binds to a regulatory component of the Kdp potassium uptake system and that this binding has an inhibitory effect on the expression of the kdp genes encoding a potassium transporter. c-di-AMP binds to the USP domain of KdpD, thus providing for the first time evidence for the ability of such a domain to bind a cyclic dinucleotide.
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Affiliation(s)
- Joana A Moscoso
- Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom
| | - Hannah Schramke
- Center for Integrated Protein Science (CiPSM), Department of Biology I, Microbiology, Ludwig-Maximilians-Universität München, Martinsried, Germany
| | - Yong Zhang
- Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom
| | - Tommaso Tosi
- Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom
| | - Amina Dehbi
- Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom
| | - Kirsten Jung
- Center for Integrated Protein Science (CiPSM), Department of Biology I, Microbiology, Ludwig-Maximilians-Universität München, Martinsried, Germany
| | - Angelika Gründling
- Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom
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14
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Abstract
Escherichia coli and Salmonella encounter osmotic pressure variations in natural environments that include host tissues, food, soil, and water. Osmotic stress causes water to flow into or out of cells, changing their structure, physics, and chemistry in ways that perturb cell functions. E. coli and Salmonella limit osmotically induced water fluxes by accumulating and releasing electrolytes and small organic solutes, some denoted compatible solutes because they accumulate to high levels without disturbing cell functions. Osmotic upshifts inhibit membrane-based energy transduction and macromolecule synthesis while activating existing osmoregulatory systems and specifically inducing osmoregulatory genes. The osmoregulatory response depends on the availability of osmoprotectants (exogenous organic compounds that can be taken up to become compatible solutes). Without osmoprotectants, K+ accumulates with counterion glutamate, and compatible solute trehalose is synthesized. Available osmoprotectants are taken up via transporters ProP, ProU, BetT, and BetU. The resulting compatible solute accumulation attenuates the K+ glutamate response and more effectively restores cell hydration and growth. Osmotic downshifts abruptly increase turgor pressure and strain the cytoplasmic membrane. Mechanosensitive channels like MscS and MscL open to allow nonspecific solute efflux and forestall cell lysis. Research frontiers include (i) the osmoadaptive remodeling of cell structure, (ii) the mechanisms by which osmotic stress alters gene expression, (iii) the mechanisms by which transporters and channels detect and respond to osmotic pressure changes, (iv) the coordination of osmoregulatory programs and selection of available osmoprotectants, and (v) the roles played by osmoregulatory mechanisms as E. coli and Salmonella survive or thrive in their natural environments.
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15
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Ribeiro VB, Destro MT. Listeria monocytogenes serotype 1/2b and 4b isolates from human clinical cases and foods show differences in tolerance to refrigeration and salt stress. J Food Prot 2014; 77:1519-26. [PMID: 25198843 DOI: 10.4315/0362-028x.jfp-13-548] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Control of Listeria monocytogenes in food processing facilities is a difficult issue because of the ability of this microorganism to form biofilms and adapt to adverse environmental conditions. Survival at high concentrations of sodium chloride and growth at refrigeration temperatures are two other important characteristics of L. monocytogenes isolates. The aim of this study was to compare the growth characteristics under stress conditions at different temperatures of L. monocytogenes serotypes responsible for the majority of clinical cases from different sources. Twenty-two L. monocytogenes isolates, 12 from clinical cases (8 serotype 4b and 4 serotype 1/2a) and 10 from food (6 serotype 4b and 4 serotype 1/2a), and an L. monocytogenes Scott A (serotype 4b) reference strain were analyzed for the ability to grow in brain heart infusion broth plus 1.9 M NaCl (11%) at 4, 10, and 25°C for 73, 42, and 15 days, respectively. The majority of L. monocytogenes strains was viable or even grew at 4°C and under the high osmotic conditions usually used to control pathogens in the food industry. At 10°C, most strains could adapt and grow; however, no significant difference (P > 0.05) was found for lag-phase duration, maximum growth rate, and maximum cell density. At 25°C, all strains were able to grow, and populations increased by up 5 log CFU/ml. Clinical strains had a significantly longer lag phase and lower maximum cell density (P < 0.05) than did food strains. Regarding virulence potential, no significant differences in hemolytic activity were found among serotypes; however, serotype 4b strains were more invasive in Caco-2 cells than were serotype 1/2a strains (P < 0.05). The global tendency of decreasing NaCl concentrations in processed foods for health reasons may facilitate L. monocytogenes survival and growth in these products. Therefore, food companies must consider additional microbial growth barriers to assure product safety.
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Affiliation(s)
- V B Ribeiro
- Department of Food and Experimental Nutrition, University of São Paulo, São Paulo 05508000, Brazil.
| | - M T Destro
- Department of Food and Experimental Nutrition, University of São Paulo, São Paulo 05508000, Brazil
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16
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Peña-Meléndez M, Perry JJ, Yousef AE. Changes in thermal resistance of three Salmonella serovars in response to osmotic shock and adaptation at water activities reduced by different humectants. J Food Prot 2014; 77:914-8. [PMID: 24853512 DOI: 10.4315/0362-028x.jfp-13-201] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The purpose of this study was to investigate the effect of osmotic shock and adaptation at low water activity (aw) and the type of humectant used to lower the aw, on heat resistance of three Salmonella enterica serovars (Saintpaul 02-109, Tennessee 2053H, and Elmsbuettel 1236H). The serovars were grown (adapted) or transferred (osmotic shocked) in low-aw broths and subjected to heat treatment at 55°C for up to 45 min; samples were removed at 5-min intervals and immediately placed in an ice-water bath until plating. The aw of tryptic soy broth (TSB) was lowered by the addition of 20% (wt/wt) glycerol (aw 0.94), 4% (wt/wt) sodium chloride (NaCl; aw 0.97), or 35% sucrose (wt/wt) (aw 0.95). The type of humectant and cell adaptation significantly affected the D55°C-value. Cells merely suspended in 20% glycerol broth (i.e., nonadapted) prior to heat treatment showed a larger D55°C-value (3.0 to 3.9 min), when compared with that of cells adapted in the same medium (D55°C-values of 0.86 to 0.98 min). Interestingly, cells adapted to TSB plus glycerol were not more resistant to heat than were the controls. NaCl and sucrose showed a net protective effect for all serovars under both the adapted and nonadapted conditions, with sucrose providing the most protection. Highest D55°C-values were obtained for cultures adapted to TSB plus sucrose. Based on these results, the effect of reduced aw on thermal resistance of Salmonella serovars varies greatly, depending on medium constituents and adaptation of the pathogen in these media.
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Affiliation(s)
- Marilia Peña-Meléndez
- Department of Food Science and Technology, The Ohio State University, Parker Food Science Building, 2015 Fyffe Road, Columbus, Ohio 43210, USA
| | - Jennifer J Perry
- Department of Food Science and Technology, The Ohio State University, Parker Food Science Building, 2015 Fyffe Road, Columbus, Ohio 43210, USA
| | - Ahmed E Yousef
- Department of Food Science and Technology, The Ohio State University, Parker Food Science Building, 2015 Fyffe Road, Columbus, Ohio 43210, USA.
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17
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Chen W, Golden D, Critzer F. Salmonella
survival and differential expression of fatty acid biosynthesis-associated genes in a low-water-activity food. Lett Appl Microbiol 2014; 59:133-8. [DOI: 10.1111/lam.12253] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Revised: 03/17/2014] [Accepted: 03/18/2014] [Indexed: 11/27/2022]
Affiliation(s)
- W. Chen
- Department of Food Science and Technology; The University of Tennessee; Knoxville TN USA
| | - D.A. Golden
- Department of Food Science and Technology; The University of Tennessee; Knoxville TN USA
| | - F.J. Critzer
- Department of Food Science and Technology; The University of Tennessee; Knoxville TN USA
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18
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Chiang ML, Chen HC, Wu C, Chen MJ. Effect of Acid Adaptation on the Environmental Stress Tolerance of Three Strains ofVibrio parahaemolyticus. Foodborne Pathog Dis 2014; 11:287-94. [DOI: 10.1089/fpd.2013.1641] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Ming-Lun Chiang
- Department of Tourism and Hospitality, Kainan University, Taoyuan, Taiwan
| | - Hsi-Chia Chen
- Food and Drug Administration, Ministry of Health and Welfare, Taipei, Taiwan
| | - Chieh Wu
- Department of Animal Science and Technology, National Taiwan University, Taipei, Taiwan
| | - Ming-Ju Chen
- Department of Animal Science and Technology, National Taiwan University, Taipei, Taiwan
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19
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Rossi-Fedele G, Guastalli AR. Osmolarity and root canal antiseptics. Int Endod J 2013; 47:314-20. [PMID: 23889531 DOI: 10.1111/iej.12153] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 06/29/2013] [Indexed: 11/30/2022]
Affiliation(s)
- G. Rossi-Fedele
- Warwick Dentistry; The University of Warwick; Coventry UK
- Pontifical Catholic University of Rio Grande do Sul; Porto Alegre RS Brazil
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20
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van der Waal SV, Jiang LM, de Soet JJ, van der Sluis LW, Wesselink PR, Crielaard W. Sodium chloride and potassium sorbate: a synergistic combination againstEnterococcus faecalisbiofilms: anin vitrostudy. Eur J Oral Sci 2012; 120:452-7. [DOI: 10.1111/j.1600-0722.2012.00982.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/01/2012] [Indexed: 11/29/2022]
Affiliation(s)
- Suzette V. van der Waal
- Department of Conservative & Preventive Dentistry; Academic Centre for Dentistry Amsterdam (ACTA); Amsterdam; the Netherlands
| | - Lei-Meng Jiang
- Department of Conservative & Preventive Dentistry; Academic Centre for Dentistry Amsterdam (ACTA); Amsterdam; the Netherlands
| | - Johannes J. de Soet
- Department of Conservative & Preventive Dentistry; Academic Centre for Dentistry Amsterdam (ACTA); Amsterdam; the Netherlands
| | - Lucas W.M. van der Sluis
- Department of Conservative Dentistry and Endodontology; Faculty of Dentistry, Paul Sabatier University; Toulouse; France
| | - Paul R. Wesselink
- Department of Conservative & Preventive Dentistry; Academic Centre for Dentistry Amsterdam (ACTA); Amsterdam; the Netherlands
| | - Wim Crielaard
- Department of Conservative & Preventive Dentistry; Academic Centre for Dentistry Amsterdam (ACTA); Amsterdam; the Netherlands
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21
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Influence of the different sodium chloride concentrations on microbiological and physico-chemical characteristics of mozzarella cheese. J DAIRY RES 2012; 79:390-6. [DOI: 10.1017/s0022029912000209] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In this work the effects of addition of different amounts of sodium chloride, during cheese making, on shelf life of mozzarella cheese were evaluated. The mozzarella cheese quality decay was assessed during storage at 9 °C by monitoring microbiological, sensory and physico-chemical changes in the product. Results showed thatPseudomonasspp. growth was responsible for cheese unacceptability, whereas the sensory quality did not limit cheese shelf life. In particular, the highest shelf life values were obtained for mozzarella without salt and with the lowest salt concentration (0·23 g NaCl), and amounted to about 5 and 4 d, respectively. On the contrary, high salt concentrations affected product shelf life, probably as a consequence of progressive solubilisation of cheese casein, due to the phenomenon of ‘salting in’.
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22
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Loveday SM, Huang VT, Reid DS, Winger RJ. Water Dynamics in Fresh and Frozen Yeasted Dough. Crit Rev Food Sci Nutr 2012; 52:390-409. [DOI: 10.1080/10408398.2010.500265] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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23
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Hennekinne JA, De Buyser ML, Dragacci S. Staphylococcus aureus and its food poisoning toxins: characterization and outbreak investigation. FEMS Microbiol Rev 2011; 36:815-36. [PMID: 22091892 DOI: 10.1111/j.1574-6976.2011.00311.x] [Citation(s) in RCA: 536] [Impact Index Per Article: 41.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 09/15/2011] [Accepted: 10/03/2011] [Indexed: 11/29/2022] Open
Abstract
Staphylococcal food poisoning (SFP) is one of the most common food-borne diseases and results from the ingestion of staphylococcal enterotoxins (SEs) preformed in food by enterotoxigenic strains of Staphylococcus aureus. To date, more than 20 SEs have been described: SEA to SElV. All of them have superantigenic activity whereas half of them have been proved to be emetic, representing a potential hazard for consumers. This review, divided into four parts, will focus on the following: (1) the worldwide story of SFP outbreaks, (2) the characteristics and behaviour of S. aureus in food environment, (3) the toxinogenic conditions and characteristics of SEs, and (4) SFP outbreaks including symptomatology, occurrence in the European Union and currently available methods used to characterize staphylococcal outbreaks.
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Affiliation(s)
- Jacques-Antoine Hennekinne
- French Agency for Food, Environmental and Occupational Health & Safety (Anses), Food Safety Laboratory of Maisons-Alfort, European Union Reference Laboratory for Coagulase Positive Staphylococci, Maisons-Alfort, France.
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24
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van der Waal SV, van der Sluis LWM, Özok AR, Exterkate RAM, van Marle J, Wesselink PR, de Soet JJ. The effects of hyperosmosis or high pH on a dual-species biofilm of Enterococcus faecalis and Pseudomonas aeruginosa: an in vitro study. Int Endod J 2011; 44:1110-7. [DOI: 10.1111/j.1365-2591.2011.01929.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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25
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Nopcharoenkul W, Pinphanichakarn P, Pinyakong O. The development of a liquid formulation of Pseudoxanthomonas sp. RN402 and its application in the treatment of pyrene-contaminated soil. J Appl Microbiol 2011; 111:36-47. [PMID: 21518158 DOI: 10.1111/j.1365-2672.2011.05037.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AIM To develop a liquid formulation of Pseudoxanthomonas sp. RN402 for prolonged storage and maintaining high survival rates and pyrene biodegradability. METHODS AND RESULTS Liquid formulations of RN402, designated as L-RN402, were prepared by suspending bacterial cells (10⁹ CFU ml⁻¹) in various buffers. Analysis found that phosphate buffer containing glycerol maintained high survival rate (94%) as well as pyrene biodegradability of bacteria after a 30-day storage. This L-RN402 could be stored at 30°C for at least 6 months. Bioaugmentation treatment with stored L-RN402 resulted in the complete degradation of pyrene (300 mg kg⁻¹) in soil microcosms within 4 weeks. RN402 could be detected by denaturing gradient gel electrophoresis throughout the period; moreover, real-time PCR indicated the presence of high number of nidA-containing bacteria. CONCLUSIONS A liquid formulation of RN402, an effective pyrene degrader, was developed by suspending RN402 in phosphate buffer containing 1% glycerol. This formulation could be stored at 30°C for at least 6 months and maintain high efficacy in the treatment of pyrene-contaminated soil. SIGNIFICANCE AND IMPACT OF THE STUDY This work is the first description of a liquid formulation of pyrene-degrading bacteria for prolonged storage that retains biological activity for the treatment of environmental pollutants.
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Affiliation(s)
- W Nopcharoenkul
- Inter-department of Environmental Science, Graduate School, Chulalongkorn University, Bangkok, Thailand
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26
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Taormina PJ. Implications of salt and sodium reduction on microbial food safety. Crit Rev Food Sci Nutr 2010; 50:209-27. [PMID: 20301012 DOI: 10.1080/10408391003626207] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Excess sodium consumption has been cited as a primary cause of hypertension and cardiovascular diseases. Salt (sodium chloride) is considered the main source of sodium in the human diet, and it is estimated that processed foods and restaurant foods contribute 80% of the daily intake of sodium in most of the Western world. However, ample research demonstrates the efficacy of sodium chloride against pathogenic and spoilage microorganisms in a variety of food systems. Notable examples of the utility and necessity of sodium chloride include the inhibition of growth and toxin production by Clostridium botulinum in processed meats and cheeses. Other sodium salts contributing to the overall sodium consumption are also very important in the prevention of spoilage and/or growth of microorganisms in foods. For example, sodium lactate and sodium diacetate are widely used in conjunction with sodium chloride to prevent the growth of Listeria monocytogenes and lactic acid bacteria in ready-to-eat meats. These and other examples underscore the necessity of sodium salts, particularly sodium chloride, for the production of safe, wholesome foods. Key literature on the antimicrobial properties of sodium chloride in foods is reviewed here to address the impact of salt and sodium reduction or replacement on microbiological food safety and quality.
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27
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Hegde A, Bhat GK, Mallya S. Effect of stress on production of heat labile enterotoxin by Escherichia coli. Indian J Med Microbiol 2009; 27:325-8. [PMID: 19736401 DOI: 10.4103/0255-0857.55446] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Enterotoxigenic Escherichia coli (ETEC) is an important pathogen responsible for secretory diarrhoea. The production of heat labile enterotoxin (LT), by ETEC, is largely responsible for the pathogenesis of diarrhoea. In the present study we investigated the effect of stress factors such as temperature, pH, osmotic stress and nutritional limitation on the production of LT by ETEC using in-house GMI-ELISA. Four strains of E. coli consisting, one standard strain MTCC 723 and three clinical isolates were used in the study. Maximum amount of LT (OD 3.285) was produced at 37 0 C followed by 40 0 C (OD 3.305). Growth of E. coli in medium with pH 8.6 resulted in maximum amount of LT production (OD 3.489). LT was not detectable when bacteria were grown in medium with pH < or =7.2 and > or = 9.2. Sodium chloride concentration of 0.2 M stimulated maximum amount of LT production. Maximum amount of LT was produced when the bacteria were grown in medium containing 2.5 g/l of glucose. All the stress factors had a significant effect on the LT production by E. coli , though quantitative differences in the various strains were observed.
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Affiliation(s)
- A Hegde
- Department of Microbiology, Kasturba Medical College, Mangalore - 575 001, India.
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28
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Rahman MS. Food Stability Beyond Water Activity and Glass Transtion: Macro-Micro Region Concept in the State Diagram. INTERNATIONAL JOURNAL OF FOOD PROPERTIES 2009. [DOI: 10.1080/10942910802628107] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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29
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Arakawa K, Kawai Y, Iioka H, Tanioka M, Nishimura J, Kitazawa H, Tsurumi K, Saito T. Effects of gassericins A and T, bacteriocins produced by Lactobacillus gasseri, with glycine on custard cream preservation. J Dairy Sci 2009; 92:2365-72. [DOI: 10.3168/jds.2008-1240] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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30
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Role of proP and proU in betaine uptake by Yersinia enterocolitica under cold and osmotic stress conditions. Appl Environ Microbiol 2008; 75:1471-7. [PMID: 19114512 DOI: 10.1128/aem.01644-08] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Yersinia enterocolitica is a food-borne pathogen with the ability to grow at cold temperatures and tolerate high osmolarity. The bacterium tolerates osmotic stress by intracellular accumulation of osmolytes, such as betaine. The proP gene and proU operon of Y. enterocolitica were sequenced, and single (ProP(-) ProU(+) and ProP(+) ProU(-)) and double (ProP(-) ProU(-)) mutants were generated. Upon exposure to osmotic or chill stress, the single and double mutants demonstrated a reduction in betaine uptake compared to that in the wild type, suggesting that proP and proU play a role in betaine uptake during osmotic and chill stress responses of Y. enterocolitica.
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31
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Lo Nostro P, Ninham BW, Milani S, Lo Nostro A, Pesavento G, Baglioni P. Hofmeister effects in supramolecular and biological systems. Biophys Chem 2006; 124:208-13. [PMID: 16678961 DOI: 10.1016/j.bpc.2006.04.004] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2005] [Revised: 04/14/2006] [Accepted: 04/14/2006] [Indexed: 11/19/2022]
Abstract
Specific ion effects, representative of near-universal Hofmeister phenomena, are illustrated in three different systems. These are the formation of supramolecular assemblies from cyclodextrins, the optical rotation of L-serine, and the growth rate of two kinds of microorganisms (Staphylococcus aureus and Pseudomonas aeruginosa). The strong specific ion effects can be correlated with the anion polarizabilities and related physico-chemical parameters. The results show the relevance of dispersion (non-electrostatic) forces in these phenomena.
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Affiliation(s)
- Pierandrea Lo Nostro
- Department of Chemistry and CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy.
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32
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Kieboom J, Kusumaningrum HD, Tempelaars MH, Hazeleger WC, Abee T, Beumer RR. Survival, elongation, and elevated tolerance of Salmonella enterica serovar Enteritidis at reduced water activity. J Food Prot 2006; 69:2681-6. [PMID: 17133811 DOI: 10.4315/0362-028x-69.11.2681] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Growing microorganisms on dry surfaces, which results in exposure to low water activity (a(w)), may change their normal morphology and physiological activity. In this study, the morphological changes and cell viability of Salmonella enterica serovar Enteritidis challenged to low a(w) were analyzed. The results indicated that exposure to reduced a(w) induced filamentation of the cells. The amount of filamentous cells at a(w) 0.94 was up to 90% of the total number of cells. Surviving filamentous cells maintained their membrane integrity after exposure to low a(w) for 21 days. Furthermore, cells prechallenged to low a(w), obtained with an ionic humectant, demonstrated higher resistance to sodium hypochlorite than control cells. These resistant cells are able to survive disinfection more efficiently and can therefore cause contamination of foods coming in contact with surfaces. This points to the need for increased attention to cleaning of surfaces in household environments and disinfection procedures in processing plants.
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Affiliation(s)
- Jasper Kieboom
- Laboratory of Food Microbiology, Department of Agrotechnology and Food Sciences, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands
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Wijnker JJ, Koop G, Lipman LJA. Antimicrobial properties of salt (NaCl) used for the preservation of natural casings. Food Microbiol 2006; 23:657-62. [PMID: 16943065 DOI: 10.1016/j.fm.2005.11.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2005] [Accepted: 11/20/2005] [Indexed: 11/28/2022]
Abstract
The antimicrobial properties of salt (NaCl) used for the preservation of natural casings were studied by investigating the survival of six bacterial species in natural casings at different water activity (aw) levels. Individual sheep casings were inoculated with ca. 10(5) colony-forming units (cfu) g(-1) of Escherichia coli, Salmonella typhimurium, Listeria monocytogenes, Staphylococcus aureus, Clostridium perfringens and 10(2)cfu g(-1) of E. coli O157:H7. The casings were stored at 20+/-1.5 degrees C in different brines and dry salt, giving aw-levels of 0.90 aw, 0.87aw, 0.85 aw, 0.83 aw and 0.75 aw. Samples were taken at day 1, 3, 6, 8, 13, 20, 27 and 30 after inoculation and the number of bacteria present was determined. Based on survival curves, death rates (day(-1)) were calculated to quantify the reduction in log10 cfu g(-1) per day. The influence of aw on death rates was higher for Gram-negative bacteria than for Gram-positive bacteria. The death rates were overall higher for Gram-negatives than for Gram-positives. No clear reduction in the survival of C. perfringens in relation to any aw level was observed in this study. These results indicate that the antimicrobial properties of salt used for the preservation of natural casings are sufficient to reduce the bacterial contamination (except for Clostridium spores) well below acceptable levels at a water activity level of 0.85 or lower during a 30-day storage period.
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Affiliation(s)
- J J Wijnker
- Van Hessen bv, Nieuwerkerk a/d IJssel, The Netherlands
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Morales P, Calzada J, Rodríguez B, de Paz M, Gaya P, Nuñez M. Effect of cheese water activity and carbohydrate content on the barotolerance of Listeria monocytogenes scott A. J Food Prot 2006; 69:1328-33. [PMID: 16786853 DOI: 10.4315/0362-028x-69.6.1328] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
High-pressure processing is an appropriate technique for improving the microbiological safety of packaged ready-to-eat foods. The effect of high-pressure treatment on Listeria monocytogenes Scott A inoculated into fresh Hispánico-type cheese and ripe Mahón cheese was investigated. A 3.8-log reduction in the counts of L. monocytogenes Scott A in fresh cheese was recorded after 3 min at 400 MPa and 12 degrees C, whereas 18 min under the same conditions was required to obtain a 1-log reduction in ripe cheese. Dry matter values were 48.96% for fresh cheese and 58.79% for ripe cheese, and water activity (aw) values were 0.983 and 0.922, respectively. In dehydrated fresh cheese (58.20% dry matter) in which 5% NaCl was added to achieve a 0.904 aw value, L. monocytogenes Scott A counts were lowered by only 0.4 log after treatment for 10 min at 400 MPa. On the other hand, in a 60:40 mixture of ripe cheese:distilled water with a 0.976 aw value, the reduction under the same conditions was 3.9 log. Within the aw range of 0.945 to 0.965, L. monocytogenes Scott A barotolerance was significantly higher in fresh cheese than in ripe cheese for equivalent aw values. Carbohydrate content was higher in fresh cheese than in ripe cheese. The addition of lactose at a concentration of 5 mg/g to an 85:15 mixture of ripe cheese:distilled water did not influence L. monocytogenes Scott A barotolerance during treatment for 10 min at 400 MPa. Galactose at a concentration of 5 mg/g had a protective effect during high-pressure treatment, and glucose at a concentration of 5 mg/g favored L. monocytogenes Scott A survival during refrigerated storage of pressurized samples at 8 degrees C for 5 days.
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Affiliation(s)
- Pilar Morales
- Departamento de Tecnología de Alimentos, Instituto Nacional de Investigación y Tecnología Agraria y Altimentaria, Carretera de La Coruña Km 7, Madrid, 28040 Spain
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Hew CM, Hajmeer MN, Farver TB, Glover JM, Cliver DO. Survival of Salmonella and Escherichia coli O157:H7 in chorizos. J Food Prot 2005; 68:2039-46. [PMID: 16245705 DOI: 10.4315/0362-028x-68.10.2039] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Mexican-style raw meat sausages (chorizos) are not regulated in California when they are produced in small ethnic food markets. These sausages are sold uncooked, but their formulation imparts a color that may lead the consumer to assume that they are already cooked, and thus the chorizos may sometimes be eaten without proper cooking. If pathogens are present in such cases, illness may result. Survival of Salmonella and Escherichia coli O157:H7 in chorizos was evaluated under different storage conditions selected based on an initial survey of uninspected chorizos in California. Chorizos were formulated with five different initial water activity (aw) values (0.85, 0.90, 0.93, 0.95, and 0.97), stored under four conditions (refrigeration at 6 to 8 degrees C, room temperature at 24 to 26 degrees C, under a hood at 24 to 26 degrees C with forced air circulation, and incubation at 30 to 31 degrees C with convective air circulation), and sampled after 1, 2, 4, and 7 days. The initial pH was 4.8 and remained near 5.0 from day 1 of the sampling period. Two separate studies of packs inoculated with five-strain cocktails of Salmonella and of E. coli O157:H7 were performed twice for each initial aw. The three lowest aw values (0.85, 0.90, and 0.93) and the incubation and hood storage conditions were more effective (P < or = 0.05) at reducing the target pathogen levels in chorizos than were the two highest aw values (0.95 and 0.97) and the refrigeration storage condition, regardless of storage time. These results provide a scientific basis for guidelines given to producers of uninspected chorizo and should reduce the probability of foodborne illness associated with these products.
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Affiliation(s)
- Carrie M Hew
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, California 95616, USA
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Stewart CM, Cole MB, Legan JD, Slade L, Schaffner DW. Solute-specific effects of osmotic stress on Staphylococcus aureus. J Appl Microbiol 2005; 98:193-202. [PMID: 15610432 DOI: 10.1111/j.1365-2672.2004.02445.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
AIM To determine if cell death from osmotic stress is because of lack of sufficient energy to maintain cell metabolism. Additionally, the solute-specific effect of five humectants on bacterial osmoregulation and cell survival was examined. METHODS AND RESULTS Staphylococcus aureus was placed into 84% relative humidity (RH) broth (five humectants used individually). ATP, ADP and cell viability measurements were determined over time. The results indicate that ATP is not the limiting factor for cell survival under excessive osmotic stress. Although the same RH was achieved with various humectants, the rates of cell death varied greatly as did the sensitivities of the cell populations to osmotic stress. CONCLUSIONS The results from this study provide strong evidence that mechanisms of osmotic inactivation depend on the solute. The molecular mobility of the system may be an important means to explain these differences. SIGNIFICANCE AND IMPACT OF THE STUDY By bringing together an understanding of solute-specific effects, microbial physiology and genetics, the mechanisms of inactivation of micro-organisms by solute-specific osmotic stress may be elucidated, and this knowledge may then be exploited to ensure the production of high quality, safe foods.
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Lo Nostro P, Ninham BW, Lo Nostro A, Pesavento G, Fratoni L, Baglioni P. Specific ion effects on the growth rates ofStaphylococcus aureusandPseudomonas aeruginosa. Phys Biol 2005; 2:1-7. [PMID: 16204851 DOI: 10.1088/1478-3967/2/1/001] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Motivated by recent advances in the physical and chemical basis of the Hofmeister effect, we measured the rate cell growth of S. aureus--a halophilic pathogenic bacterium--and of P. aeruginosa, an opportunistic pathogen, in the presence of different aqueous salt solutions at different concentrations (0.2, 0.6 and 0.9 M). Microorganism growth rates depend strongly on the kind of anion in the growth medium. In the case of S. aureus, chloride provides a favorable growth medium, while both kosmotropes (water structure makers) and chaotropes (water structure breakers) reduce the microorganism growth. In the case of P. aeruginosa, all ions affect adversely the bacterial survival. In both cases, the trends parallel the specific ion, or Hofmeister, sequences observed in a wide range of physico-chemical systems. The correspondence with specific ion effect obtained in other studies, on the activities of a DNA restriction enzyme, of horseradish peroxidase, and of Lipase A (Aspergillus niger) is particularly striking. This work provides compelling evidence for Hofmeister effects, physical chemistry in action, in these organisms.
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Affiliation(s)
- Pierandrea Lo Nostro
- Department of Chemistry and CSGI, University of Florence, via della Lastruccia 3-50019 Sesto Fiorentino (Firenze), Italy.
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Beales N. Adaptation of Microorganisms to Cold Temperatures, Weak Acid Preservatives, Low pH, and Osmotic Stress: A Review. Compr Rev Food Sci Food Saf 2004; 3:1-20. [DOI: 10.1111/j.1541-4337.2004.tb00057.x] [Citation(s) in RCA: 459] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Munsey TS, Mohindra A, Yusaf SP, Grainge A, Wang MH, Wray D, Sivaprasadarao A. Functional properties of Kch, a prokaryotic homologue of eukaryotic potassium channels. Biochem Biophys Res Commun 2002; 297:10-6. [PMID: 12220501 DOI: 10.1016/s0006-291x(02)02095-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To test the hypothesis that the Kch gene of Escherichia coli encodes a potassium channel, we have transformed E. coli with an expression vector containing the Kch sequence and observed the effect of over-expression of Kch on E. coli. We found that: (i) over-expression of Kch is toxic to E. coli, but the toxicity could be prevented by supplementing the growth medium with K(+), Rb(+), and NH(4)(+), but not Na(+), consistent with the properties of a potassium selective pore; (ii) Cs(+), a blocker of potassium channels, rescues the growth of Kch over-expressing cells; and (iii) when the putative pore-forming region of Kch, containing the signature sequence, was replaced with the corresponding region of the eukaryotic Shaker potassium channel, and the resultant construct expressed in E. coli, the cells became critically dependent on K(+) supply for survival. These data are consistent with the proposed function of Kch, i.e., K(+) conduction.
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Affiliation(s)
- Tim S Munsey
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
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40
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Wood JM, Bremer E, Csonka LN, Kraemer R, Poolman B, van der Heide T, Smith LT. Osmosensing and osmoregulatory compatible solute accumulation by bacteria. Comp Biochem Physiol A Mol Integr Physiol 2001; 130:437-60. [PMID: 11913457 DOI: 10.1016/s1095-6433(01)00442-1] [Citation(s) in RCA: 292] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Bacteria inhabit natural and artificial environments with diverse and fluctuating osmolalities, salinities and temperatures. Many maintain cytoplasmic hydration, growth and survival most effectively by accumulating kosmotropic organic solutes (compatible solutes) when medium osmolality is high or temperature is low (above freezing). They release these solutes into their environment when the medium osmolality drops. Solutes accumulate either by synthesis or by transport from the extracellular medium. Responses to growth in high osmolality medium, including biosynthetic accumulation of trehalose, also protect Salmonella typhimurium from heat shock. Osmotically regulated transporters and mechanosensitive channels modulate cytoplasmic solute levels in Bacillus subtilis, Corynebacterium glutamicum, Escherichia coli, Lactobacillus plantarum, Lactococcus lactis, Listeria monocytogenes and Salmonella typhimurium. Each organism harbours multiple osmoregulatory transporters with overlapping substrate specificities. Membrane proteins that can act as both osmosensors and osmoregulatory transporters have been identified (secondary transporters ProP of E. coli and BetP of C. glutamicum as well as ABC transporter OpuA of L. lactis). The molecular bases for the modulation of gene expression and transport activity by temperature and medium osmolality are under intensive investigation with emphasis on the role of the membrane as an antenna for osmo- and/or thermosensors.
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Affiliation(s)
- J M Wood
- Department of Microbiology and Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Guelph, Canada.
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Leblanc L, Gouffi K, Leroi F, Hartke A, Blanco C, Auffray Y, Pichereau V. Uptake of choline from salmon flesh and its conversion to glycine betaine in response to salt stress in Shewanella putrefaciens. Int J Food Microbiol 2001; 65:93-103. [PMID: 11322705 DOI: 10.1016/s0168-1605(00)00516-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
When cultured in M63 minimal medium plus 0.6 M NaCl, the growth of Shewanella putrefaciens was strongly inhibited. The addition of an extract from smoked salmon to this medium restored the growth almost to the unstressed level. A comparison of the 13C NMR spectra of intracellular solutes extracted from S. putrefaciens cells cultured in both conditions revealed the accumulation of glycine betaine (GB) from the smoked salmon extract (SSE). Analysis of the osmoprotective properties of this extract for several strains of Escherichia coli (which differ from each other in their ability to accumulate GB (i) from the surrounding environment, and (ii) from its hydroxylated precursor choline), demonstrated the absence of GB in the SSE. From the overall results, we inferred that salt-stressed S. putrefaciens cells accumulated GB from choline present in the SSE. Furthermore, the use of [14C]-labeled betaines gave evidence that S. putrefaciens (i) oxidised choline to GB, (ii) accumulated GB as a non-metabolisable osmolyte (up to 1300 nmol (mg dw)(-1) when cultured in a medium containing 0.5 M NaCl and either 1 mM choline or 1 mM GB), and (iii) both choline and GB uptake activities were osmotically upregulated (both activities were increased more than 50-fold in media containing 0.4 to 0.6 M NaCl). In all, our results suggest that in salted smoked salmon, S. putrefaciens imports and oxidises choline, leading to the intracellular accumulation of GB.
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Affiliation(s)
- L Leblanc
- Laboratoire de Microbiologie de l'Environnement, USC INRA EA956, IRBA, Université de Caen, France
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Pichereau V, Hartke A, Auffray Y. Starvation and osmotic stress induced multiresistances. Influence of extracellular compounds. Int J Food Microbiol 2000; 55:19-25. [PMID: 10791712 DOI: 10.1016/s0168-1605(00)00208-7] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Growth restriction due to stasis and/or hyperosmolarity is a common situation encountered by microorganisms in nature. Therefore, they have developed defence systems allowing them to withstand these periods. Bacteria respond to these conditions by a metabolic reprogramming which leads to a cellular state of enhanced resistance. This communication reviews recent advances in knowledge of the molecular basis of this phenomenon in different bacteria.
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Affiliation(s)
- V Pichereau
- Laboratoire de Microbiologie de l'Environnement, Institut de Recherche en Biologie appliquée, Université de Caen, France.
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43
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Abstract
Bacteria can survive dramatic osmotic shifts. Osmoregulatory responses mitigate the passive adjustments in cell structure and the growth inhibition that may ensue. The levels of certain cytoplasmic solutes rise and fall in response to increases and decreases, respectively, in extracellular osmolality. Certain organic compounds are favored over ions as osmoregulatory solutes, although K+ fluxes are intrinsic to the osmoregulatory response for at least some organisms. Osmosensors must undergo transitions between "off" and "on" conformations in response to changes in extracellular water activity (direct osmosensing) or resulting changes in cell structure (indirect osmosensing). Those located in the cytoplasmic membranes and nucleoids of bacteria are positioned for indirect osmosensing. Cytoplasmic membrane-based osmosensors may detect changes in the periplasmic and/or cytoplasmic solvent by experiencing changes in preferential interactions with particular solvent constituents, cosolvent-induced hydration changes, and/or macromolecular crowding. Alternatively, the membrane may act as an antenna and osmosensors may detect changes in membrane structure. Cosolvents may modulate intrinsic biomembrane strain and/or topologically closed membrane systems may experience changes in mechanical strain in response to imposed osmotic shifts. The osmosensory mechanisms controlling membrane-based K+ transporters, transcriptional regulators, osmoprotectant transporters, and mechanosensitive channels intrinsic to the cytoplasmic membrane of Escherichia coli are under intensive investigation. The osmoprotectant transporter ProP and channel MscL act as osmosensors after purification and reconstitution in proteoliposomes. Evidence that sensor kinase KdpD receives multiple sensory inputs is consistent with the effects of K+ fluxes on nucleoid structure, cellular energetics, cytoplasmic ionic strength, and ion composition as well as on cytoplasmic osmolality. Thus, osmoregulatory responses accommodate and exploit the effects of individual cosolvents on cell structure and function as well as the collective contribution of cosolvents to intracellular osmolality.
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Affiliation(s)
- J M Wood
- Department of Microbiology and Guelph-Waterloo Centre for Graduate Work in Chemistry, University of Guelph, Guelph, Ontario, Canada N1G
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Abstract
During harvesting, processing and handling operations food may become contaminated with a wide range of microorganisms. Subsequently, during distribution and storage only a small fraction of these will develop and cause serious deteriorations. Which microorganisms will develop or what (bio)chemical reactions occur is dependent upon food derived or environmental factors. This paper will describe the main mechanisms involved in the loss of food quality for the most important food commodities. Food spoilage may be caused by a wide range of reactions including some that are mainly physical or chemical, others due to action of enzymes or microorganisms. The primary factors associated with food spoilage are associated with intrinsic food properties (e.g., endogenous enzymes, substrates, sensitivity for light, oxygen) and (cross)contamination during harvesting, slaughter and processing in combination with temperature abuse. For fresh foods the primary quality changes may be categorized as (i) bacterial growth and metabolism resulting in possible pH-changes and formation of toxic compounds, off-odours, gas and slime-formation, (ii) oxidation of lipids and pigments in fat-containing foods resulting in undesirable flavours, formation of compounds with adverse biological effects or discoloration. Although interrelated with the microbial spoilage, the last category is 'purely' chemical in nature and will, all other things being equal, increase in importance with decreasing temperature. Little is known about the relationship between microbial activity and (bio)chemical spoilage parameters under different packaging and storage conditions. Although there is much progress in the characterisation of the total microflora and metabolites developing during spoilage, not much is known about the identification of specific microorganisms in relation to food composition. Despite the fact that food spoilage is a huge economical problem world wide, it is obvious that the mechanisms and interaction leading to food spoilage are very poorly understood.
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Affiliation(s)
- J H Huis in 't Veld
- Department of Food of Animal Origin, Faculty of Veterinary Medicine, Utrecht University, Netherlands
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Abstract
There is potential for spoilage of all foods at some rate or other following harvest, slaughter or manufacture and spoilage may occur at any of the stages between the acquisition of raw materials and the eventual consumption of a food product. These stages include processing, packaging, distribution, retail display, transport, storage and use by the consumer. They are under varying degrees of control that aim to deliver a satisfactory shelf life, to ensure that the finally-consumed product is of high quality and to ensure that it is safe. Spoilage may be caused by a wide range of reactions including some that are essentially physical, some that are chemical, some enzymic and some microbiological. The various forms of microbiological spoilage are preventable to a large degree by a wide range of preservation techniques, most of which act by preventing or inhibiting microbial growth (e.g., chilling, freezing, drying, curing, conserving, vacuum packing, modified atmosphere packing, acidifying, fermenting and adding preservatives). A smaller number of techniques act by inactivating microorganisms (e.g., pasteurization, sterilization and irradiation). Additional techniques restrict the access of microorganisms to products (e.g., aseptic processing and packaging. A major trend is that new and emerging preservation techniques which are coming into use or are under development include more that act by inactivation (e.g., ultrahigh pressure, electroporation, manothermosonication and addition of bacteriolytic enzymes). A further trend is towards the use of procedures that deliver products that are less heavily preserved, have higher quality, are more natural, freer from additives and nutritionally healthier. Less severe preservation procedures are therefore being developed that make use of preservative factors in combinations to deliver (a) less damage to product quality (hurdle technologies); (b) new methods of heating that are better controlled and therefore deliver milder heat to products; (c) cook-chill combinations that deliver longer high quality shelf lives: (d) modified atmosphere packaging to retain quality longer; and (e) use of antimicrobial systems that are more natural. Many of the existing and emerging preservation techniques act by interfering with the homeostatic mechanisms that microorganisms have evolved in order to survive extreme environmental stresses.
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