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 simulta- neously with enteric pathogenic strains (enterotoxigenic Escherichia coli K88 or Salmonella typhimurium SARB21 and SL1344), before pathogenic strains and after patho- genic strains for competition, exclusion and displacement assays. The six lactobacilli significantly limited the adhe- sion and invasion of the pathogenic bacteria. In the simu- lating 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 ± 0.10 log CFU/well) was much lower than the control group without Lactobacillus (5.98 ± 0.02 log CFU/well). Compared to the control group (6.07 ± 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 ± 0.04 log CFU/well). These results implied that several Lactobacillus strains might be useful for pro- tecting against enteric pathogenic infection.