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.
Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden ; Department of Forest Products, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.
Biomed Res Int. 2014;2014:471317. doi: 10.1155/2014/471317. Epub 2014 Jul 8.
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.
在与发酵香肠相关的浓度下（pH 值 4.6、150mM 乳酸、aw = 0.92、温度 = 20 或 27°C），大肠杆菌对乳酸的敏感性会随着生长速率的增加而提高。对于在 TSB 中培养的大肠杆菌 683 菌株，在恒化器或分批培养中，当暴露于乳酸胁迫时，随后的失活动力会随着收获时的生长速率增加而增加。发现收获时的生长速率与失活动力之间存在线性关系，可以描述分批培养和恒化器培养。在分批培养的前 3 小时收获的细菌之间，T90 的最大差异（估计对数减少的时间）为 10 小时，即生长速率不同。根据温度与失活动力之间的关系，T90 的 10 小时差异相当于在 33°C 或 45°C 而不是 37°C 测量失活动力。在相似的收获生长速率下，在 37°C 培养的细菌的失活动力低于在 15-20°C 培养的细菌。如大肠杆菌 683 所示，导致生长速率变化的培养条件可能导致乳酸失活动力的变化。研究结果强调了使用和报告标准化培养条件的重要性，并可能对开发失活动力学模型时数据解释产生影响。
