Cell surface proteins play an important role in probiotic activities of Lactobacillus reuteri

Background: Eight Lactobacillus reuteri strains, previously isolated from breast-fed human infant feces, were selected to assess the potential contribution of their surface proteins in probiotic activity. These strains were treated with 5 M LiCl to remove their surface proteins, and their tolerance to simulated stomach-duodenum passage, cell surface characteristics, autoaggregation, adhesion, and inhibition of pathogen adhesion to Caco-2 cells were compared with untreated strains. Results: The survival rates, autoaggregation, and adhesion abilities of the LiCl-treated L. reuteri strains decreased significantly (p < 0.05) compared to that of the untreated cells. The inhibition ability of selected L. reuteri strains, untreated or LiCl treated, against adherence of Escherichia coli 25922 and Salmonella typhi NCDC113 to Caco-2 was evaluated in vitro with L. reuteri ATCC55730 strain as a positive control. Among the selected eight strains of L. reuteri, LR6 showed maximum inhibition against the E. coli ATCC25922 and S. typhi NCDC113. After treatment with 5 M LiCl to remove surface protein, the inhibition activities of the lactobacilli against pathogens decreased significantly (p < 0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that LR6 strains had several bands with molecular weight ranging from 10 to 100 KDa, and their characterization and functions need to be confirmed. Conclusions: The results revealed that the cell surface proteins of L. reuteri play an important role in their survivability, adhesion, and competitive exclusion of pathogen to epithelial cells.