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Specific growth rate determines the sensitivity of Escherichia coli to lactic acid stress: implications for predictive microbiology.

Lindqvist R, Barmark G - Biomed Res Int (2014)

Bottom Line: A linear relationship between growth rate at harvest and inactivation rate was found to describe both batch and chemostat cultures.As demonstrated for E. coli 683, culture conditions leading to variable growth rates may contribute to variable lactic acid inactivation rates.Findings emphasize the use and reporting of standardised culture conditions and can have implications for the interpretation of data when developing inactivation models.

View Article: PubMed Central - PubMed

Affiliation: Division of Risk and Benefit Assessment, National Food Agency, 75126 Uppsala, Sweden ; Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden ; Department of Microbiology, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.

ABSTRACT
This study tested the hypothesis that sensitivity of Escherichia coli to lactic acid at concentrations relevant for fermented sausages (pH 4.6, 150 mM lactic acid, aw = 0.92, temperature = 20 or 27°C) increases with increasing growth rate. For E. coli strain 683 cultured in TSB in chemostat or batch, subsequent inactivation rates when exposed to lactic acid stress increased with increasing growth rate at harvest. A linear relationship between growth rate at harvest and inactivation rate was found to describe both batch and chemostat cultures. The maximum difference in T90, the estimated times for a one-log reduction, was 10 hours between bacteria harvested during the first 3 hours of batch culture, that is, at different growth rates. A 10-hour difference in T90 would correspond to measuring inactivation at 33°C or 45°C instead of 37°C based on relationships between temperature and inactivation. At similar harvest growth rates, inactivation rates were lower for bacteria cultured at 37°C than at 15-20°C. As demonstrated for E. coli 683, culture conditions leading to variable growth rates may contribute to variable lactic acid inactivation rates. Findings emphasize the use and reporting of standardised culture conditions and can have implications for the interpretation of data when developing inactivation models.

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Growth curve of E. coli 683 in TSB batch culture (shaken Erlenmeyer flask) at 37°C (●, ln OD600). The specific growth rate μ (Δ, h−1) was calculated as the slope of five adjacent points.
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fig3: Growth curve of E. coli 683 in TSB batch culture (shaken Erlenmeyer flask) at 37°C (●, ln OD600). The specific growth rate μ (Δ, h−1) was calculated as the slope of five adjacent points.

Mentions: Replicate inactivation rates determined for bacteria harvested at approximately the same growth rates varied less than 0.09 h−1 (chemostat) and 0.12 h−1 (batch) or within a factor of about two (Table 2). In comparison, the maximum difference in inactivation rates for bacteria harvested at all different growth rates was 0.35 h−1 (chemostat) and 0.47 h−1 (batch), respectively (Table 2). In relative terms, mean inactivation rates varied by a factor of 8 (0.40/0.05) and 48 (0.48/0.01) times, for E. coli cells cultured in chemostat and batch, respectively. Growth rates at harvest varied between 0.17 and 1.90 h−1 (chemostat) and between 0 and 1.77 h−1 (batch), respectively (Table 2). Thus, variation in growth rates at harvest may influence subsequent estimates of inactivation rates unless care is taken to control this parameter. Growth rates of E. coli cultured in batch in TSB medium estimated based on OD600 measurements decreased continuously until the stationary phase and the maximum difference during the initial 3 hours was ca 1.7 h−1 (Figure 3). This indicates the magnitude of variation in growth rates under the present conditions.


Specific growth rate determines the sensitivity of Escherichia coli to lactic acid stress: implications for predictive microbiology.

Lindqvist R, Barmark G - Biomed Res Int (2014)

Growth curve of E. coli 683 in TSB batch culture (shaken Erlenmeyer flask) at 37°C (●, ln OD600). The specific growth rate μ (Δ, h−1) was calculated as the slope of five adjacent points.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4109666&req=5

fig3: Growth curve of E. coli 683 in TSB batch culture (shaken Erlenmeyer flask) at 37°C (●, ln OD600). The specific growth rate μ (Δ, h−1) was calculated as the slope of five adjacent points.
Mentions: Replicate inactivation rates determined for bacteria harvested at approximately the same growth rates varied less than 0.09 h−1 (chemostat) and 0.12 h−1 (batch) or within a factor of about two (Table 2). In comparison, the maximum difference in inactivation rates for bacteria harvested at all different growth rates was 0.35 h−1 (chemostat) and 0.47 h−1 (batch), respectively (Table 2). In relative terms, mean inactivation rates varied by a factor of 8 (0.40/0.05) and 48 (0.48/0.01) times, for E. coli cells cultured in chemostat and batch, respectively. Growth rates at harvest varied between 0.17 and 1.90 h−1 (chemostat) and between 0 and 1.77 h−1 (batch), respectively (Table 2). Thus, variation in growth rates at harvest may influence subsequent estimates of inactivation rates unless care is taken to control this parameter. Growth rates of E. coli cultured in batch in TSB medium estimated based on OD600 measurements decreased continuously until the stationary phase and the maximum difference during the initial 3 hours was ca 1.7 h−1 (Figure 3). This indicates the magnitude of variation in growth rates under the present conditions.

Bottom Line: A linear relationship between growth rate at harvest and inactivation rate was found to describe both batch and chemostat cultures.As demonstrated for E. coli 683, culture conditions leading to variable growth rates may contribute to variable lactic acid inactivation rates.Findings emphasize the use and reporting of standardised culture conditions and can have implications for the interpretation of data when developing inactivation models.

View Article: PubMed Central - PubMed

Affiliation: Division of Risk and Benefit Assessment, National Food Agency, 75126 Uppsala, Sweden ; Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden ; Department of Microbiology, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.

ABSTRACT
This study tested the hypothesis that sensitivity of Escherichia coli to lactic acid at concentrations relevant for fermented sausages (pH 4.6, 150 mM lactic acid, aw = 0.92, temperature = 20 or 27°C) increases with increasing growth rate. For E. coli strain 683 cultured in TSB in chemostat or batch, subsequent inactivation rates when exposed to lactic acid stress increased with increasing growth rate at harvest. A linear relationship between growth rate at harvest and inactivation rate was found to describe both batch and chemostat cultures. The maximum difference in T90, the estimated times for a one-log reduction, was 10 hours between bacteria harvested during the first 3 hours of batch culture, that is, at different growth rates. A 10-hour difference in T90 would correspond to measuring inactivation at 33°C or 45°C instead of 37°C based on relationships between temperature and inactivation. At similar harvest growth rates, inactivation rates were lower for bacteria cultured at 37°C than at 15-20°C. As demonstrated for E. coli 683, culture conditions leading to variable growth rates may contribute to variable lactic acid inactivation rates. Findings emphasize the use and reporting of standardised culture conditions and can have implications for the interpretation of data when developing inactivation models.

Show MeSH
Related in: MedlinePlus