Inhibition of Shigella sonnei adherence to HT-29 cells by lactobacilli from Chinese fermented food and preliminary characterization of S-layer protein involvement

In this study, seven lactobacilli with a high degree of antagonistic activity against three pathogens and good adherence to HT-29 cells were selected. The ability of these seven lactobacilli to inhibit adhesion of Shigella sonnei to intestinal mucosa was studied on cultured HT-29 cells. Lactobacilli were added simultaneously with, before or after S. sonnei to test for their effectiveness in exclusion, competition and displacement assays, respectively. Lactobacillus paracasei subp. paracasei M5-L, Lactobacillus rhamnosus J10-L and Lactobacillus casei Q8-L all exhibited significant inhibitory activity. In order to elucidate the inhibitory functions of S-layer proteins, the S-layer proteins were removed with 5 M LiCl from the M5-L, J10-L and Q8-L strains. Under such conditions, inhibition activity was decreased in all three strains, as revealed in exclusion, competition and displacement assays. SDS-PAGE analysis confirmed the presence of S-layer proteins with dominant bands of approximately 45 kDa. Further analysis of S-layer proteins revealed that the hydrophobic amino acids accounted for 40.5%, 41.5% and 43.8% of the total amino acid for the M5-L, J10-L and Q8-L strains, respectively. These findings suggest that the M5-L, J10-L and Q8-L strains possess the ability to inhibit S. sonnei adherence to HT-29 cells, and S-layer proteins are involved in this adhesion inhibition.