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BioMed Research International
Volume 2014, Article ID 471317, 8 pages
http://dx.doi.org/10.1155/2014/471317
Research Article

Specific Growth Rate Determines the Sensitivity of Escherichia coli to Lactic Acid Stress: Implications for Predictive Microbiology

1Division of Risk and Benefit Assessment, National Food Agency, 75126 Uppsala, Sweden
2Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden
3Department of Microbiology, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden
4Department of Forest Products, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden

Received 24 April 2014; Accepted 18 June 2014; Published 8 July 2014

Academic Editor: Antonio Valero

Copyright © 2014 Roland Lindqvist and Gunilla Barmark. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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, , 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.