Effect of sub-lethal chemical disinfection on the biofilm forming ability, resistance to antibiotics and expression of virulence genes of <i>Salmonella</i> Enteritidis biofilm-surviving cells

Abstract

Although disinfection procedures are widely implemented in food environments, bacteria can survive and present increased virulence/resistance. Since little is known about these phenomena regarding biofilms, this study aimed to investigate the effect of chemical disinfection on biofilm-derived cells of <i>Salmonella</i> Enteritidis. Using a reference strain (NCTC 13349) and a food isolate (350), biofilm susceptibility to benzalkonium chloride (BAC), sodium hypochlorite (SH) and hydrogen peroxide (HP) was evaluated and biofilms were exposed to sub-lethal concentrations of each disinfectant. Biofilm-derived cells were characterized for their biofilm forming ability, antibiotic resistance and expression of virulence-associated genes. Except for a few instances, disinfectant exposure did not alter antibiotic susceptibility. However, SH and HP exposure enhanced the biofilm forming ability of <i>Salmonella</i> Enteritidis NCTC 13349. After BAC and HP exposure, biofilm-derived cells presented a down-regulation of <i>rpoS</i>. Exposure to BAC also revealed an up-regulation of <i>invA, avrA</i> and <i>csgD</i> on <i>Salmonella</i> Enteritidis NCTC 13349. The results obtained suggest that biofilm-derived cells that survive disinfection may represent an increased health risk.