The virulence regulator PrfA plays a significant role in the Listeria monocytogenes biofilm formation

Abstract:

The ability of the foodborne pathogen Listeria monocytogenes to develop biofilm in food-processing environment is a major concern for the food safety, because formation of biofilm facilitates bacteria to survive in the adverse environment and resist desiccation, UV light and treatment with antimicrobial and sanitizing agents. However, the molecular mechanism of biofilm formation in L. monocytogenes has not been fully understood. PrfA is a key transcriptional activator that positively regulates most of the known listerial virulence genes expression. In order to explore the role of PrfA on Listeria biofilm development, we compared the abilities of biofilm formation in this study for L. monocytogenes wild type strains (EGD and EGDe) and their prfA deletion mutants (EGD??prfA and EGDe??prfA), nonpathogenic Listeria innocua, as well as the recombinant strains that can constitutively express PrfA in L. innocua (LI-pERL3-prfA*) and in EGDe??prfA (EGDe?prfA-pERL3-prfA*). Our results showed that the wild types of L. monocytogenes had strong abilities to develop “a network of knitted chains” biofilm structures on polyvinyl chloride microtiter plates, while unstructured biofilm was observed in L. innocua. Biofilm formation was reduced in L. monocytogenes mutants lacking PrfA and rescued in the strain with constitutive expression of PrfA. However, PrfA had no impact on L. innocua biofilm formation. Our results suggest that PrfA plays a significant role only in the L. monocytogenes biofilm formation but not in L. innocua. PrfA might indirectly regulate expression of certain genes involving in L. monocytogenes biofilm formation.