Sodium chloride affects Listeria monocytogenes adhesion to polystyrene and stainless steel by regulating flagella expression

Aim: To study the adhesion capability of seven strains of Listeria monocytogenes to polystyrene and stainless steel surfaces after cultivation at various NaCl concentrations. Methods and Results: Determination of growth limits indicated that all seven strains were able to grow in up to 11% NaCl in rain heart infusion and 3 g l-1 yeast extract-glucose at 20 degrees C, but no growth was detected at 15% NaCl. Adhesion of L. monocytogenes was estimated after 4-h incubation at 20 degrees C in 96-well microtitre plates. Statistical results revealed no significant difference between adhesion to polystyrene and stainless steel although surface properties were different. Adhesion between 0% and 6% NaCl was not different, whereas adhesion at 11% NaCl was significantly lower. This discrepancy in adhesion was correlated with the down-regulation of flagella at 11% NaCl. Conclusions: Only high salinity levels, close to nongrowth conditions, repressed the expression of flagella, and consequently, decreased the adhesion capability of L. monocytogenes. Significance and Impact of the Study: Adhesion of L. monocytogenes to inert surfaces depends on environmental conditions that affect flagellum expression. High salinity concentrations would delay biofilm formation.