Effect of NaCl on the biofilm formation by foodborne pathogens

This study was designed to evaluate the effect of NaCl on the biofilm formation of Listeria monocytogenes, Staphylococcus aureus, Shigella boydii, and Salmonella Typhimurium. The biofilm cells were cultured in media containing different NaCl concentrations (0% to 10%) for 10 d of incubation at 37 °C using a 24-well polystyrene microtiter plate, collected by swabbing methods, and enumerated using plate count method. The attachment and detachment kinetic patterns were estimated according to the modified Gompertz model. The cell surface hydrophobicity and auto-aggregation were observed at different NaCl concentrations. Most strains showed 2 distinctive phases at lower than 6% NaCl, while the numbers of adhered cells gradually increased throughout the incubation period at 4% to 10% NaCl. At 0% NaCl, the numbers of adhered L. monocytogenes, S. aureus, S. boydii, and S. Typhimurium cells rapidly increased up to 7.04, 6.47, 6.39, and 7.27 log CFU/cm(2), respectively, within 4 d of incubation. The maximum growth rate (k(A)) and specific growth rate (μ(A)) of adherent pathogenic cells were decreased with increasing NaCl concentration. Noticeable decline in the numbers of adherent cells was observed at low concentration levels of NaCl (<2%). The adherence abilities of foodborne pathogens were influenced by the physicochemical surface properties. The hydrophobicity and auto-aggregation enhanced the biofilm formation during the incubation periods. Therefore, this study could provide useful information to better understand the adhesion and detachment capability of foodborne pathogens on food contact surfaces.