Influence of acid stress on survival, expression of virulence genes and invasion capacity into Caco-2 cells of Listeria monocytogenes strains of different origins

The influence of food-related acid stress on the virulence capacity of Listeria monocytogenes was evaluated. The survival of acid-adapted and non-adapted L. monocytogenes cells during exposure to lethal concentrations of acetic acid was monitored. Also the effect of sublethal acid stress exposure on the expression levels of several virulence genes and on the capacity to invade Caco-2 cells was analyzed. Acid-adapted and non-adapted cells showed different acid tolerance response (ATR) patterns. Our data also demonstrate that pre-exposure to sublethal acid stress might lead to gadD2 induction. However, no correlation with the origin of the strain and with the ATR was noticed, indicating that probably other genes also could play an important role in this ATR mechanism. Additionally, our data showed that acid adaptation could influence the virulence capacity by regulating the expression levels of virulence genes. Moreover, the inlA expression data strongly correlated with the results of the in vitro invasion study. These results lead to the indication that low pH and acetic acid, used in minimally processed food products, might influence the virulence potential of L. monocytogenes.