Salmonella enterica Serovar Typhimurium and Listeria monocytogenes Acid Tolerance Response Induced by Organic Acids at 20°C: Optimization and Modeling

An acid tolerance response (ATR) has been demonstrated in Listeria monocytogenes and Salmonella enterica serovar Typhimurium in response to low pH poised (i.e., adapted) with acetic or lactic acids at 20°C and modeled by using dynamic differential equations. The ATR was not immediate or prolonged, and optimization occurred after exposure of L. monocytogenes for 3 h at pH 5.5 poised with acetic acid and for 2 h at pH 5.5 poised with lactic acid and after exposure of S. enterica serovar Typhimurium for 2 h at pH 5.5 poised with acetic acid and for 3 h at pH 5.5 poised with lactic acid. An objective mechanistic analysis of the acid inactivation data yielded estimates of the duration of the shoulder (t_s), the log-linear decline (k_max), and the magnitude of a critical component (C). The magnitude of k_max gave the best agreement with estimates of conditions for optimum ATR induction made from the raw data.