Effect of Bacteriocins and Conditions that Mimic Food and Digestive Tract on Biofilm Formation, In Vitro Invasion of Eukaryotic Cells and Internalin Gene Expression by Listeria monocytogenes.

In this report, Listeria monocytogenes isolates were evaluated for their ability to form biofilms, for adhesion/invasion of eukaryotic cells and for differential expression of internalin A (inl A) gene, which is related to virulence potential. The presence of bacteriocins of lactic acid bacteria and incubation at 5 °C were the main factors that influenced biofilm formation by L. monocytogenes, in comparison with BHI (control). In general, adhesion and invasion of Caco-2 cells were significantly lower in low pH (4.5), in incubation at 5 °C and in the presence of Oxgall 0.3 %. On the other hand, two L. monocytogenes isolates (INCQS 353 and Reg 26c) showed higher invasion rates when cultivated in the presence of NaCl 5 % (P < 0.05). One L. monocytogenes isolate (H-2) showed the strongest ability to form biofilm and to invade Caco-2 cells, under selected conditions, suggesting there is a relationship between biofilm formation and virulence potential. For all isolates, expression of inl A gene was down-regulated by the presence of bacteriocins, Oxgall 0.3 %, pH 4.5 and incubation at 5 °C. Nonetheless, for one L. monocytogenes isolate (HU 471), expression of inl A gene was eight times higher in the presence of sucrose, indicating that food components can increase the infectiveness of L. monocytogenes.