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Louis Coroller - One of the best experts on this subject based on the ideXlab platform.
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differentiation of vegetative cells into spores a kinetic model applied to bacillus subtilis
Applied and Environmental Microbiology, 2019Co-Authors: Emilie Gauvry, Annegabrielle Mathot, Olivier Couvert, Matthieu Jules, Ivan Leguérinel, Louis CorollerAbstract:ABSTRACT Spore-forming bacteria are natural contaminants of food raw materials, and Sporulation can occur in many environments from farm to fork. In order to characterize and to predict spore formation over time, we developed a model that describes both the kinetics of growth and the differentiation of vegetative cells into spores. The model is based on a classical growth model and enables description of the kinetics of Sporulation with the addition of three parameters specific to Sporulation. Two parameters are related to the probability of each vegetative cell to commit to Sporulation and to form a spore, and the last one is related to the time needed to form a spore once the cell is committed to Sporulation. The goodness of fit of this growth-Sporulation model was assessed using growth-Sporulation kinetics at various temperatures in laboratory medium or in whey for Bacillus subtilis, Bacillus cereus, and Bacillus licheniformis. The model accurately describes the kinetics in these different conditions, with a mean error lower than 0.78 log10 CFU/ml for the growth and 1.08 log10 CFU/ml for the Sporulation. The biological meaning of the parameters was validated with a derivative strain of Bacillus subtilis 168 which produces green fluorescent protein at the initiation of Sporulation. This model provides physiological information on the spore formation and on the temporal abilities of vegetative cells to differentiate into spores and reveals the heterogeneity of spore formation during and after growth. IMPORTANCE The growth-Sporulation model describes the progressive transition from vegetative cells to spores with Sporulation parameters describing the Sporulation potential of each vegetative cell. Consequently, the model constitutes an interesting tool to assess the Sporulation potential of a bacterial population over time with accurate parameters such as the time needed to obtain one resistant spore and the probability of Sporulation. Further, this model can be used to assess these data under various environmental conditions in order to better identify the conditions favorable for Sporulation regarding the time to obtain the first spore and/or the concentrations of spores which could be reached during a food process.
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differentiation of vegetative cells into spores a kinetic model applied to bacillus subtilis
bioRxiv, 2018Co-Authors: Emilie Gauvry, Annegabrielle Mathot, Olivier Couvert, Matthieu Jules, Ivan Leguérinel, Louis CorollerAbstract:Bacterial spores are formed within vegetative cells as thick-walled bodies resistant to physical and chemical treatments which allow the persistence and dissemination of the bacterial species. Spore-forming bacteria are natural contaminants of food raw materials and Sporulation can occur in many environments from farm to fork. In order to predict spore formation over time, we developed a model that describes both the kinetics of growth and the differentiation of vegetative cells into spores. The model includes a classical growth model with the addition of only two Sporulation-specific parameters: the probability of each vegetative cell to sporulate, and the time needed to form a spore once the cell is committed to Sporulation. The growth-Sporulation model was evaluated using the spore-forming, Gram positive bacterium, Bacillus subtilis and the biological meaning of the Sporulation-specific parameters was validated using a derivative strain that produces the green fluorescent protein as a marker of Sporulation initiation. The model accurately describes the growth and the Sporulation kinetics in different environmental conditions and further provides valuable, physiological information on the temporal abilities of vegetative cells to differentiate into spores.
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Knowledge of the physiology of spore-forming bacteria can explain the origin of spores in the food environment.
Research in Microbiology, 2016Co-Authors: Emilie Gauvry, Florence Postollec, Annegabrielle Mathot, Olivier Couvert, Ivan Leguérinel, Veronique Broussolle, Louis CorollerAbstract:Abstract Spore-forming bacteria are able to grow under a wide range of environmental conditions, to form biofilms and to differentiate into resistant forms: spores. This resistant form allows their dissemination in the environment; consequently, they may contaminate raw materials. Sporulation can occur all along the food chain, in raw materials, but also in food processes, leading to an increase in food contamination. However, the problem of Sporulation during food processing is poorly addressed and Sporulation niches are difficult to identify from the farm to the fork. Sporulation is a survival strategy. Some environmental factors are required to trigger this differentiation process and others act by modulating it. The efficiency of Sporulation is the result of the combined effects of these two types of factors on vegetative cell metabolism. This paper aims to explain and help identify Sporulation niches in the food chain, based on features of spore-former physiology.
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Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and aw.
Food Microbiology, 2012Co-Authors: Eugénie Baril, Florence Postollec, Olivier Couvert, Louis Coroller, Ivan Leguérinel, Mohammed El Jabri, Christophe Boulais, Frédéric Carlin, Pierre MafartAbstract:Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and a w a b s t r a c t Sporulation niches in the food chain are considered as a source of hazard and are not clearly identified. Determining the Sporulation environmental boundaries could contribute to identify potential sporula-tion niches. Spore formation was determined in a Sporulation Mineral Buffer. The effect of incubation temperature, pH and water activity on time to one spore per mL, maximum Sporulation rate and final spore concentration was investigated for a Bacillus weihenstephanensis and a Bacillus licheniformis strain. Sporulation boundaries of B. weihenstephanensis and of B. licheniformis were similar to, or included within, the range of temperatures, pH and water activities supporting growth. For instance, Sporulation boundaries of B. weihenstephanensis were evaluated at 5 C, 35 C, pH 5.2 and a w 0.960 while growth boundaries were observed at 5 C, 37 C, pH 4.9 and a w 0.950. Optimum spore formation was determined at 30 C pH 7.2 for B. weihenstephanensis and at 45 C pH 7.2 for B. licheniformis. Lower temperatures and pH delayed the Sporulation process. For instance, the time to one spore per mL was tenfold longer when Sporulation occurred at 10 C and 20 C, for each strain respectively, than at optimum Sporulation temperature. The relative effect of temperature and pH on Sporulation rates and on growth rates is similar. This work suggests that the influence of environmental factors on the quantitative changes in Sporulation boundaries and rates was similar to their influence on changes in growth rate.
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The wet-heat resistance of Bacillus weihenstephanensis KBAB4 spores produced in a two-step Sporulation process depends on Sporulation temperature but not on previous cell history.
International Journal of Food Microbiology, 2011Co-Authors: E Baril, Florence Postollec, Louis Coroller, Ivan Leguérinel, C Boulais, F Carlin, P MafartAbstract:While bacterial spores are mostly produced in a continuous process, this study reports a two-step Sporulation methodology. Even though spore heat resistance of numerous spore-forming bacteria is known to be dependent on Sporulation conditions, this approach enables the distinction between the vegetative cell growth phase in nutrient broth and the Sporulation phase in specific buffer. This study aims at investigating whether the conditions of growth of the vegetative cells, prior to Sporulation, could affect spore heat resistance. For that purpose, wet-heat resistance of Bacillus weihenstephanensis KBAB4 spores, produced via a two-step Sporulation process, was determined from vegetative cells harvested at four different stages of the growth kinetics, i.e. early exponential phase, late exponential phase, transition phase or early stationary phase. To assess the impact of the temperature on spore heat resistance, Sporulation was performed at 10 °C, 20 °C and 30 °C from cells grown during a continuous or a discontinuous temperature process, differentiating or not the growth and Sporulation temperatures. Induction of Sporulation seems possible for a large range of growth stages. Final spore concentration was not significantly affected by the vegetative cell growth stage while it was by the temperature during growing and Sporulation steps. The Sporulation temperature influences the heat resistance of B. weihenstephanensis KBAB4 spores much more than growth temperature prior to Sporulation. Spores produced at 10 °C were up to 3 times less heat resistant than spores produced at 30 °C.
Ivan Leguérinel - One of the best experts on this subject based on the ideXlab platform.
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differentiation of vegetative cells into spores a kinetic model applied to bacillus subtilis
Applied and Environmental Microbiology, 2019Co-Authors: Emilie Gauvry, Annegabrielle Mathot, Olivier Couvert, Matthieu Jules, Ivan Leguérinel, Louis CorollerAbstract:ABSTRACT Spore-forming bacteria are natural contaminants of food raw materials, and Sporulation can occur in many environments from farm to fork. In order to characterize and to predict spore formation over time, we developed a model that describes both the kinetics of growth and the differentiation of vegetative cells into spores. The model is based on a classical growth model and enables description of the kinetics of Sporulation with the addition of three parameters specific to Sporulation. Two parameters are related to the probability of each vegetative cell to commit to Sporulation and to form a spore, and the last one is related to the time needed to form a spore once the cell is committed to Sporulation. The goodness of fit of this growth-Sporulation model was assessed using growth-Sporulation kinetics at various temperatures in laboratory medium or in whey for Bacillus subtilis, Bacillus cereus, and Bacillus licheniformis. The model accurately describes the kinetics in these different conditions, with a mean error lower than 0.78 log10 CFU/ml for the growth and 1.08 log10 CFU/ml for the Sporulation. The biological meaning of the parameters was validated with a derivative strain of Bacillus subtilis 168 which produces green fluorescent protein at the initiation of Sporulation. This model provides physiological information on the spore formation and on the temporal abilities of vegetative cells to differentiate into spores and reveals the heterogeneity of spore formation during and after growth. IMPORTANCE The growth-Sporulation model describes the progressive transition from vegetative cells to spores with Sporulation parameters describing the Sporulation potential of each vegetative cell. Consequently, the model constitutes an interesting tool to assess the Sporulation potential of a bacterial population over time with accurate parameters such as the time needed to obtain one resistant spore and the probability of Sporulation. Further, this model can be used to assess these data under various environmental conditions in order to better identify the conditions favorable for Sporulation regarding the time to obtain the first spore and/or the concentrations of spores which could be reached during a food process.
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differentiation of vegetative cells into spores a kinetic model applied to bacillus subtilis
bioRxiv, 2018Co-Authors: Emilie Gauvry, Annegabrielle Mathot, Olivier Couvert, Matthieu Jules, Ivan Leguérinel, Louis CorollerAbstract:Bacterial spores are formed within vegetative cells as thick-walled bodies resistant to physical and chemical treatments which allow the persistence and dissemination of the bacterial species. Spore-forming bacteria are natural contaminants of food raw materials and Sporulation can occur in many environments from farm to fork. In order to predict spore formation over time, we developed a model that describes both the kinetics of growth and the differentiation of vegetative cells into spores. The model includes a classical growth model with the addition of only two Sporulation-specific parameters: the probability of each vegetative cell to sporulate, and the time needed to form a spore once the cell is committed to Sporulation. The growth-Sporulation model was evaluated using the spore-forming, Gram positive bacterium, Bacillus subtilis and the biological meaning of the Sporulation-specific parameters was validated using a derivative strain that produces the green fluorescent protein as a marker of Sporulation initiation. The model accurately describes the growth and the Sporulation kinetics in different environmental conditions and further provides valuable, physiological information on the temporal abilities of vegetative cells to differentiate into spores.
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Knowledge of the physiology of spore-forming bacteria can explain the origin of spores in the food environment.
Research in Microbiology, 2016Co-Authors: Emilie Gauvry, Florence Postollec, Annegabrielle Mathot, Olivier Couvert, Ivan Leguérinel, Veronique Broussolle, Louis CorollerAbstract:Abstract Spore-forming bacteria are able to grow under a wide range of environmental conditions, to form biofilms and to differentiate into resistant forms: spores. This resistant form allows their dissemination in the environment; consequently, they may contaminate raw materials. Sporulation can occur all along the food chain, in raw materials, but also in food processes, leading to an increase in food contamination. However, the problem of Sporulation during food processing is poorly addressed and Sporulation niches are difficult to identify from the farm to the fork. Sporulation is a survival strategy. Some environmental factors are required to trigger this differentiation process and others act by modulating it. The efficiency of Sporulation is the result of the combined effects of these two types of factors on vegetative cell metabolism. This paper aims to explain and help identify Sporulation niches in the food chain, based on features of spore-former physiology.
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Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and aw.
Food Microbiology, 2012Co-Authors: Eugénie Baril, Florence Postollec, Olivier Couvert, Louis Coroller, Ivan Leguérinel, Mohammed El Jabri, Christophe Boulais, Frédéric Carlin, Pierre MafartAbstract:Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and a w a b s t r a c t Sporulation niches in the food chain are considered as a source of hazard and are not clearly identified. Determining the Sporulation environmental boundaries could contribute to identify potential sporula-tion niches. Spore formation was determined in a Sporulation Mineral Buffer. The effect of incubation temperature, pH and water activity on time to one spore per mL, maximum Sporulation rate and final spore concentration was investigated for a Bacillus weihenstephanensis and a Bacillus licheniformis strain. Sporulation boundaries of B. weihenstephanensis and of B. licheniformis were similar to, or included within, the range of temperatures, pH and water activities supporting growth. For instance, Sporulation boundaries of B. weihenstephanensis were evaluated at 5 C, 35 C, pH 5.2 and a w 0.960 while growth boundaries were observed at 5 C, 37 C, pH 4.9 and a w 0.950. Optimum spore formation was determined at 30 C pH 7.2 for B. weihenstephanensis and at 45 C pH 7.2 for B. licheniformis. Lower temperatures and pH delayed the Sporulation process. For instance, the time to one spore per mL was tenfold longer when Sporulation occurred at 10 C and 20 C, for each strain respectively, than at optimum Sporulation temperature. The relative effect of temperature and pH on Sporulation rates and on growth rates is similar. This work suggests that the influence of environmental factors on the quantitative changes in Sporulation boundaries and rates was similar to their influence on changes in growth rate.
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The wet-heat resistance of Bacillus weihenstephanensis KBAB4 spores produced in a two-step Sporulation process depends on Sporulation temperature but not on previous cell history.
International Journal of Food Microbiology, 2011Co-Authors: E Baril, Florence Postollec, Louis Coroller, Ivan Leguérinel, C Boulais, F Carlin, P MafartAbstract:While bacterial spores are mostly produced in a continuous process, this study reports a two-step Sporulation methodology. Even though spore heat resistance of numerous spore-forming bacteria is known to be dependent on Sporulation conditions, this approach enables the distinction between the vegetative cell growth phase in nutrient broth and the Sporulation phase in specific buffer. This study aims at investigating whether the conditions of growth of the vegetative cells, prior to Sporulation, could affect spore heat resistance. For that purpose, wet-heat resistance of Bacillus weihenstephanensis KBAB4 spores, produced via a two-step Sporulation process, was determined from vegetative cells harvested at four different stages of the growth kinetics, i.e. early exponential phase, late exponential phase, transition phase or early stationary phase. To assess the impact of the temperature on spore heat resistance, Sporulation was performed at 10 °C, 20 °C and 30 °C from cells grown during a continuous or a discontinuous temperature process, differentiating or not the growth and Sporulation temperatures. Induction of Sporulation seems possible for a large range of growth stages. Final spore concentration was not significantly affected by the vegetative cell growth stage while it was by the temperature during growing and Sporulation steps. The Sporulation temperature influences the heat resistance of B. weihenstephanensis KBAB4 spores much more than growth temperature prior to Sporulation. Spores produced at 10 °C were up to 3 times less heat resistant than spores produced at 30 °C.
Pierre Mafart - One of the best experts on this subject based on the ideXlab platform.
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Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and aw.
Food Microbiology, 2012Co-Authors: Eugénie Baril, Florence Postollec, Olivier Couvert, Louis Coroller, Ivan Leguérinel, Mohammed El Jabri, Christophe Boulais, Frédéric Carlin, Pierre MafartAbstract:Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and a w a b s t r a c t Sporulation niches in the food chain are considered as a source of hazard and are not clearly identified. Determining the Sporulation environmental boundaries could contribute to identify potential sporula-tion niches. Spore formation was determined in a Sporulation Mineral Buffer. The effect of incubation temperature, pH and water activity on time to one spore per mL, maximum Sporulation rate and final spore concentration was investigated for a Bacillus weihenstephanensis and a Bacillus licheniformis strain. Sporulation boundaries of B. weihenstephanensis and of B. licheniformis were similar to, or included within, the range of temperatures, pH and water activities supporting growth. For instance, Sporulation boundaries of B. weihenstephanensis were evaluated at 5 C, 35 C, pH 5.2 and a w 0.960 while growth boundaries were observed at 5 C, 37 C, pH 4.9 and a w 0.950. Optimum spore formation was determined at 30 C pH 7.2 for B. weihenstephanensis and at 45 C pH 7.2 for B. licheniformis. Lower temperatures and pH delayed the Sporulation process. For instance, the time to one spore per mL was tenfold longer when Sporulation occurred at 10 C and 20 C, for each strain respectively, than at optimum Sporulation temperature. The relative effect of temperature and pH on Sporulation rates and on growth rates is similar. This work suggests that the influence of environmental factors on the quantitative changes in Sporulation boundaries and rates was similar to their influence on changes in growth rate.
Olivier Couvert - One of the best experts on this subject based on the ideXlab platform.
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differentiation of vegetative cells into spores a kinetic model applied to bacillus subtilis
Applied and Environmental Microbiology, 2019Co-Authors: Emilie Gauvry, Annegabrielle Mathot, Olivier Couvert, Matthieu Jules, Ivan Leguérinel, Louis CorollerAbstract:ABSTRACT Spore-forming bacteria are natural contaminants of food raw materials, and Sporulation can occur in many environments from farm to fork. In order to characterize and to predict spore formation over time, we developed a model that describes both the kinetics of growth and the differentiation of vegetative cells into spores. The model is based on a classical growth model and enables description of the kinetics of Sporulation with the addition of three parameters specific to Sporulation. Two parameters are related to the probability of each vegetative cell to commit to Sporulation and to form a spore, and the last one is related to the time needed to form a spore once the cell is committed to Sporulation. The goodness of fit of this growth-Sporulation model was assessed using growth-Sporulation kinetics at various temperatures in laboratory medium or in whey for Bacillus subtilis, Bacillus cereus, and Bacillus licheniformis. The model accurately describes the kinetics in these different conditions, with a mean error lower than 0.78 log10 CFU/ml for the growth and 1.08 log10 CFU/ml for the Sporulation. The biological meaning of the parameters was validated with a derivative strain of Bacillus subtilis 168 which produces green fluorescent protein at the initiation of Sporulation. This model provides physiological information on the spore formation and on the temporal abilities of vegetative cells to differentiate into spores and reveals the heterogeneity of spore formation during and after growth. IMPORTANCE The growth-Sporulation model describes the progressive transition from vegetative cells to spores with Sporulation parameters describing the Sporulation potential of each vegetative cell. Consequently, the model constitutes an interesting tool to assess the Sporulation potential of a bacterial population over time with accurate parameters such as the time needed to obtain one resistant spore and the probability of Sporulation. Further, this model can be used to assess these data under various environmental conditions in order to better identify the conditions favorable for Sporulation regarding the time to obtain the first spore and/or the concentrations of spores which could be reached during a food process.
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differentiation of vegetative cells into spores a kinetic model applied to bacillus subtilis
bioRxiv, 2018Co-Authors: Emilie Gauvry, Annegabrielle Mathot, Olivier Couvert, Matthieu Jules, Ivan Leguérinel, Louis CorollerAbstract:Bacterial spores are formed within vegetative cells as thick-walled bodies resistant to physical and chemical treatments which allow the persistence and dissemination of the bacterial species. Spore-forming bacteria are natural contaminants of food raw materials and Sporulation can occur in many environments from farm to fork. In order to predict spore formation over time, we developed a model that describes both the kinetics of growth and the differentiation of vegetative cells into spores. The model includes a classical growth model with the addition of only two Sporulation-specific parameters: the probability of each vegetative cell to sporulate, and the time needed to form a spore once the cell is committed to Sporulation. The growth-Sporulation model was evaluated using the spore-forming, Gram positive bacterium, Bacillus subtilis and the biological meaning of the Sporulation-specific parameters was validated using a derivative strain that produces the green fluorescent protein as a marker of Sporulation initiation. The model accurately describes the growth and the Sporulation kinetics in different environmental conditions and further provides valuable, physiological information on the temporal abilities of vegetative cells to differentiate into spores.
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Knowledge of the physiology of spore-forming bacteria can explain the origin of spores in the food environment.
Research in Microbiology, 2016Co-Authors: Emilie Gauvry, Florence Postollec, Annegabrielle Mathot, Olivier Couvert, Ivan Leguérinel, Veronique Broussolle, Louis CorollerAbstract:Abstract Spore-forming bacteria are able to grow under a wide range of environmental conditions, to form biofilms and to differentiate into resistant forms: spores. This resistant form allows their dissemination in the environment; consequently, they may contaminate raw materials. Sporulation can occur all along the food chain, in raw materials, but also in food processes, leading to an increase in food contamination. However, the problem of Sporulation during food processing is poorly addressed and Sporulation niches are difficult to identify from the farm to the fork. Sporulation is a survival strategy. Some environmental factors are required to trigger this differentiation process and others act by modulating it. The efficiency of Sporulation is the result of the combined effects of these two types of factors on vegetative cell metabolism. This paper aims to explain and help identify Sporulation niches in the food chain, based on features of spore-former physiology.
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Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and aw.
Food Microbiology, 2012Co-Authors: Eugénie Baril, Florence Postollec, Olivier Couvert, Louis Coroller, Ivan Leguérinel, Mohammed El Jabri, Christophe Boulais, Frédéric Carlin, Pierre MafartAbstract:Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and a w a b s t r a c t Sporulation niches in the food chain are considered as a source of hazard and are not clearly identified. Determining the Sporulation environmental boundaries could contribute to identify potential sporula-tion niches. Spore formation was determined in a Sporulation Mineral Buffer. The effect of incubation temperature, pH and water activity on time to one spore per mL, maximum Sporulation rate and final spore concentration was investigated for a Bacillus weihenstephanensis and a Bacillus licheniformis strain. Sporulation boundaries of B. weihenstephanensis and of B. licheniformis were similar to, or included within, the range of temperatures, pH and water activities supporting growth. For instance, Sporulation boundaries of B. weihenstephanensis were evaluated at 5 C, 35 C, pH 5.2 and a w 0.960 while growth boundaries were observed at 5 C, 37 C, pH 4.9 and a w 0.950. Optimum spore formation was determined at 30 C pH 7.2 for B. weihenstephanensis and at 45 C pH 7.2 for B. licheniformis. Lower temperatures and pH delayed the Sporulation process. For instance, the time to one spore per mL was tenfold longer when Sporulation occurred at 10 C and 20 C, for each strain respectively, than at optimum Sporulation temperature. The relative effect of temperature and pH on Sporulation rates and on growth rates is similar. This work suggests that the influence of environmental factors on the quantitative changes in Sporulation boundaries and rates was similar to their influence on changes in growth rate.
Florence Postollec - One of the best experts on this subject based on the ideXlab platform.
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Knowledge of the physiology of spore-forming bacteria can explain the origin of spores in the food environment.
Research in Microbiology, 2016Co-Authors: Emilie Gauvry, Florence Postollec, Annegabrielle Mathot, Olivier Couvert, Ivan Leguérinel, Veronique Broussolle, Louis CorollerAbstract:Abstract Spore-forming bacteria are able to grow under a wide range of environmental conditions, to form biofilms and to differentiate into resistant forms: spores. This resistant form allows their dissemination in the environment; consequently, they may contaminate raw materials. Sporulation can occur all along the food chain, in raw materials, but also in food processes, leading to an increase in food contamination. However, the problem of Sporulation during food processing is poorly addressed and Sporulation niches are difficult to identify from the farm to the fork. Sporulation is a survival strategy. Some environmental factors are required to trigger this differentiation process and others act by modulating it. The efficiency of Sporulation is the result of the combined effects of these two types of factors on vegetative cell metabolism. This paper aims to explain and help identify Sporulation niches in the food chain, based on features of spore-former physiology.
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Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and aw.
Food Microbiology, 2012Co-Authors: Eugénie Baril, Florence Postollec, Olivier Couvert, Louis Coroller, Ivan Leguérinel, Mohammed El Jabri, Christophe Boulais, Frédéric Carlin, Pierre MafartAbstract:Sporulation boundaries and spore formation kinetics of Bacillus spp. as a function of temperature, pH and a w a b s t r a c t Sporulation niches in the food chain are considered as a source of hazard and are not clearly identified. Determining the Sporulation environmental boundaries could contribute to identify potential sporula-tion niches. Spore formation was determined in a Sporulation Mineral Buffer. The effect of incubation temperature, pH and water activity on time to one spore per mL, maximum Sporulation rate and final spore concentration was investigated for a Bacillus weihenstephanensis and a Bacillus licheniformis strain. Sporulation boundaries of B. weihenstephanensis and of B. licheniformis were similar to, or included within, the range of temperatures, pH and water activities supporting growth. For instance, Sporulation boundaries of B. weihenstephanensis were evaluated at 5 C, 35 C, pH 5.2 and a w 0.960 while growth boundaries were observed at 5 C, 37 C, pH 4.9 and a w 0.950. Optimum spore formation was determined at 30 C pH 7.2 for B. weihenstephanensis and at 45 C pH 7.2 for B. licheniformis. Lower temperatures and pH delayed the Sporulation process. For instance, the time to one spore per mL was tenfold longer when Sporulation occurred at 10 C and 20 C, for each strain respectively, than at optimum Sporulation temperature. The relative effect of temperature and pH on Sporulation rates and on growth rates is similar. This work suggests that the influence of environmental factors on the quantitative changes in Sporulation boundaries and rates was similar to their influence on changes in growth rate.
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The wet-heat resistance of Bacillus weihenstephanensis KBAB4 spores produced in a two-step Sporulation process depends on Sporulation temperature but not on previous cell history.
International Journal of Food Microbiology, 2011Co-Authors: E Baril, Florence Postollec, Louis Coroller, Ivan Leguérinel, C Boulais, F Carlin, P MafartAbstract:While bacterial spores are mostly produced in a continuous process, this study reports a two-step Sporulation methodology. Even though spore heat resistance of numerous spore-forming bacteria is known to be dependent on Sporulation conditions, this approach enables the distinction between the vegetative cell growth phase in nutrient broth and the Sporulation phase in specific buffer. This study aims at investigating whether the conditions of growth of the vegetative cells, prior to Sporulation, could affect spore heat resistance. For that purpose, wet-heat resistance of Bacillus weihenstephanensis KBAB4 spores, produced via a two-step Sporulation process, was determined from vegetative cells harvested at four different stages of the growth kinetics, i.e. early exponential phase, late exponential phase, transition phase or early stationary phase. To assess the impact of the temperature on spore heat resistance, Sporulation was performed at 10 °C, 20 °C and 30 °C from cells grown during a continuous or a discontinuous temperature process, differentiating or not the growth and Sporulation temperatures. Induction of Sporulation seems possible for a large range of growth stages. Final spore concentration was not significantly affected by the vegetative cell growth stage while it was by the temperature during growing and Sporulation steps. The Sporulation temperature influences the heat resistance of B. weihenstephanensis KBAB4 spores much more than growth temperature prior to Sporulation. Spores produced at 10 °C were up to 3 times less heat resistant than spores produced at 30 °C.
