Influence of lactic acid and post-treatment recovery time on the heat resistance of Listeria monocytogenes

We investigated the effect of short-term lactic acid treatment on the risk of Listeria monocytogenes (Lm), taking into consideration the manner of its practical use in food manufacturing processes were investigated. Since foods typically have a waiting period after LA treatment until the next processing step, the effects of the post-treatment time on the recovery of heat tolerance of Lm were also evaluated in the presence of bacterial medium as a representative of organic material. And then, We revealed that heat resistance of Lm was remarkably enhanced after acid treatment depending on the recovery time in the presence of organic matter. Further, the expression of genes related to the stress response, including sigB, was examined using RNA-seq and RT-PCR in order to elucidate the mechanism of the enhanced heat resistance of Lm following lactic acid treatment. As a result, RNA-seq and RT-PCR analyses demonstrated that several chaperones, SOS proteins and products of genes associated with heat resistance are involved in the mechanism.