Comparative evaluation of adhesion, surface properties, and surface protein composition of Listeria monocytogenes strains after cultivation at constant pH of 5 and 7

Aims: To analyse the cellular mechanisms that influence Listeria monocytogenes adhesion onto inert surfaces under acidic growth conditions. Methods and Results: The adhesion capability of all the strains was significantly reduced after cultivation at constant pH 5 than at constant pH 7 and the cell surface was significantly less hydrophobic at pH 5 than at 7. At pH 5, the analyses of surface protein composition revealed that the flagellin was downregulated for all strains, which was confirmed by the absence of flagella and the P60 protein was upregulated for L. monocytogenes EGD-e, X-Li-mo 500 and 111. The use of L. monocytogenes EGD mutants revealed that flagellin could be involved in the adhesion process, but not P60 protein. It was also observed that the hydrophobic character was not linked to the presence or the absence of flagellin or P60 protein at the cell surface of L. monocytogenes. Conclusions: The decrease of L. monocytogenes adhesion at pH 5 could be attributed to the downregulation of the flagellin synthesis under the acidic conditions. Significance and Impact of the Study: Conservation of food product at pH 5 will delay bacterial adhesion and biofilm formation during food processing on inert surfaces when the product is contaminated with L. monocytogenes.