Antagonistic activity of Lactobacillus acidophilus ATCC 4356 S-layer protein on Salmonella enterica subsp. enterica serovar Typhimurium in Caco-2 cells

Abstract

To gain insight into the mechanism of Lactobacillus S-layer protein in antimicrobial activity, we examined how the Lactobacillus acidophilus ATCC 4356 S-layer protein inhibited the adhesion and invasion of Salmonella enterica subsp. enterica serovar Typhimurium SL1344 (Salmonella Typhimurium SL1344) in vitro in cultured Caco-2 cells. The results showed that S-layer protein reduced Salmonella Typhimurium SL1344 association in Caco-2 cells by 69–88% in the adhesive experiments (competition, exclusion, and displacement assays). Although the antagonistic activity was demonstrated in the exclusion assay (preincubated with the S-layer protein), a greater effect for the S-layer protein on Salmonella Typhimurium was observed when Salmonella Typhimurium was coincubated with the S-layer protein. The S-layer protein could be bound directly to the Caco-2 cell line or be associated with Salmonella Typhimurium surface, thereby blocking Salmonella attachment. The data support the antimicrobial mechanisms of Lactobacillus S-layer protein, which are involved not only in competition for binding sites on the surface of host epithelial cells, but also in a direct interaction between this protein and Salmonella Typhimurium surface.