Ability of Lactobacillus to inhibit enteric pathogenic bacteria adhesion on Caco-2 cells

The antagonistic effects of Lactobacillus against pathogenic bacteria were evaluated in vitro on cultured Caco-2 cells. Lactobacilli were added simultaneously with enteric pathogenic strains (enterotoxigenic Escherichia coli K88 or Salmonella typhimurium SARB21 and SL1344), before pathogenic strains and after pathogenic strains for competition, exclusion and displacement assays. The six lactobacilli significantly limited the adhesion and invasion of the pathogenic bacteria. In the simulating competition and exclusion assays, the adhesion of pathogenic strains was reduced by Lactobacillus strains significantly, whereas the inhibiting effect on pathogenic strains adhesion was a little weaker in the displacement assay. Furthermore, we found that the antagonistic effects of lactobacilli against K88, SARB21, and SL1344 were various. Strain R4 showed a strong inhibitory effect on the adhesion of K88 to Caco-2 cells. In the competition assay of R4, the number of viable cell-associated K88 (3.84 +/- A 0.10 log CFU/well) was much lower than the control group without Lactobacillus (5.98 +/- A 0.02 log CFU/well). Compared to the control group (6.07 +/- A 0.02 log CFU/well), the six Lactobacillus strains all performed strong antagonistic effects against SL1344, particularly D17 showed a higher inhibitory effect in the displacement assays (4.15 +/- A 0.04 log CFU/well). These results implied that several Lactobacillus strains might be useful for protecting against enteric pathogenic infection.