Limits...
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.

Show MeSH

Related in: MedlinePlus

Relationship between estimated inactivation rate in BHI (27°C, pH = 4.6, 150 mM lactic acid, aw = 0.92) and growth rate at harvest for E. coli 683 cultured at 37°C in 25% (□) or 100% (■) TSB: (a) batch culture and (b) chemostat culture. Lines and equations represent the best fit by linear regression.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4109666&req=5

fig2: Relationship between estimated inactivation rate in BHI (27°C, pH = 4.6, 150 mM lactic acid, aw = 0.92) and growth rate at harvest for E. coli 683 cultured at 37°C in 25% (□) or 100% (■) TSB: (a) batch culture and (b) chemostat culture. Lines and equations represent the best fit by linear regression.

Mentions: E. coli were harvested from TSB batch cultures at different specific growth rates, that is, at different time points on the growth curve, and were exposed to lactic acid stress at 27°C (Table 1). There was a significant effect of growth rate on the subsequent inactivation rate (P < 0.001, GLM), and inactivation was slower for cells with lower specific growth rates than for faster growing cells (Figure 2(a)). The same pattern was observed for E. coli cells cultured in chemostat at similar growth rates, that is, dilution rates, and exposed to the same stress (Figure 2(b)).


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)

Relationship between estimated inactivation rate in BHI (27°C, pH = 4.6, 150 mM lactic acid, aw = 0.92) and growth rate at harvest for E. coli 683 cultured at 37°C in 25% (□) or 100% (■) TSB: (a) batch culture and (b) chemostat culture. Lines and equations represent the best fit by linear regression.
© Copyright Policy
Related In: Results  -  Collection

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

fig2: Relationship between estimated inactivation rate in BHI (27°C, pH = 4.6, 150 mM lactic acid, aw = 0.92) and growth rate at harvest for E. coli 683 cultured at 37°C in 25% (□) or 100% (■) TSB: (a) batch culture and (b) chemostat culture. Lines and equations represent the best fit by linear regression.
Mentions: E. coli were harvested from TSB batch cultures at different specific growth rates, that is, at different time points on the growth curve, and were exposed to lactic acid stress at 27°C (Table 1). There was a significant effect of growth rate on the subsequent inactivation rate (P < 0.001, GLM), and inactivation was slower for cells with lower specific growth rates than for faster growing cells (Figure 2(a)). The same pattern was observed for E. coli cells cultured in chemostat at similar growth rates, that is, dilution rates, and exposed to the same stress (Figure 2(b)).

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