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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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Estimated inactivation rates and standard error of the estimate (error bar) of “stationary phase” E. coli during lactic acid stress (150 mM HLac, pH = 4.6, aw = 0.92) at 27°C. Data represents results from inactivation experiments with bacteria harvested after varying times of batch culturing in TSB at 37°C.
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fig4: Estimated inactivation rates and standard error of the estimate (error bar) of “stationary phase” E. coli during lactic acid stress (150 mM HLac, pH = 4.6, aw = 0.92) at 27°C. Data represents results from inactivation experiments with bacteria harvested after varying times of batch culturing in TSB at 37°C.

Mentions: Inactivation rates of batch cultivated E. coli cells harvested in the “stationary phase” displayed a variation greater than that within a factor of two experimental variations (Figure 4) observed for replicate experiments at similar growth rates greater than zero (previous paragraph and Table 2). Further, when estimated inactivation rates of bacteria are compared based on when bacteria were harvested, expressed as the time from the start of the experiment, it is indicated that larger inactivation rates are associated with bacteria sampled early or late in the growth curve (Figure 4). These results suggest that cells sampled after 5 hours were not yet in stationary phase and that postgrowth processes become increasingly important for the sensitivity of E. coli to lactic acid stress during extended no-growth 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)

Estimated inactivation rates and standard error of the estimate (error bar) of “stationary phase” E. coli during lactic acid stress (150 mM HLac, pH = 4.6, aw = 0.92) at 27°C. Data represents results from inactivation experiments with bacteria harvested after varying times of batch culturing in TSB at 37°C.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: Estimated inactivation rates and standard error of the estimate (error bar) of “stationary phase” E. coli during lactic acid stress (150 mM HLac, pH = 4.6, aw = 0.92) at 27°C. Data represents results from inactivation experiments with bacteria harvested after varying times of batch culturing in TSB at 37°C.
Mentions: Inactivation rates of batch cultivated E. coli cells harvested in the “stationary phase” displayed a variation greater than that within a factor of two experimental variations (Figure 4) observed for replicate experiments at similar growth rates greater than zero (previous paragraph and Table 2). Further, when estimated inactivation rates of bacteria are compared based on when bacteria were harvested, expressed as the time from the start of the experiment, it is indicated that larger inactivation rates are associated with bacteria sampled early or late in the growth curve (Figure 4). These results suggest that cells sampled after 5 hours were not yet in stationary phase and that postgrowth processes become increasingly important for the sensitivity of E. coli to lactic acid stress during extended no-growth 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