Inhibition of Salmonella typhimurium adhesion to Caco-2 cell cultures by Lactobacillus strain GG spent culture supernate: only a pH effect?

The effect of Lactobacillus GG and its spent culture supernate on the adhesion of Salmonella typhimurium to Caco-2 cells was investigated. Lactobacillus GG cells which had adhered to Caco-2 monolayers prior to the addition of S. typhimurium did not inhibit the adhesion. Adhesion of S. typhimurium was reduced in the presence of spent culture supernate from MRS broth cultures (spent culture supernate I). Similar inhibition was observed with acidified fresh MRS. The viability experiments with Caco-2 cells indicated that the inhibition was presumably due to the death of cells under acidic conditions. Adhesion of S. typhimurium was reduced by pre-treating the bacteria with spent culture supernate I or with acidified MRS and whey broth prior to adhesion to Caco-2 monolayers. Pre-treatment with spent culture supernate II (from whey broth cultures) did not influence the adhesion. No inhibition was detected at neutral pH values. Therefore, the observed inhibition of S. typhimurium adhesion to Caco-2 monolayers with spent culture supernate I was most likely a pH effect.