Ability of Lactobacillus gasseri K7 to inhibit Escherichia coli adhesion in vitro on Caco-2 cells and ex vivo on pigsʹ jejunal tissue

The ability of Lactobacillus (Lb.) gasseri K7 to inhibit adhesion of Escherichia coli O8:K88 to intestinal mucosa was studied on cultured Caco-2 cells and ex vivo on pigsʹ small intestinal tissue. Lactobacilli were added simultaneously with E. coli, before E. coli and after E. coli for competition, exclusion and displacement assays. The concentration of lactobacilli on fully differentiated Caco-2 cells was 4.5 ± 0.3 × 108 cfu/well, while the concentration of E. coli varied from 1.5 × 106 to 4.3 × 108 cfu/well. The number of E. coli adhered to Caco-2 monolayer (cfu/well) was lineary correlated (R2 = 0.97) to the concentration of added cells. In the assay simulating exclusion, E. coli adhesion was reduced by Lb. gasseri K7 strain by 0.1 to 0.6 log cfu/well. The binding of E. coli was inhibited even more when incubated simultaneously with lactobacilli, particularly at the lowest concentration of E. coli (ratio E. coli/lactobacilli 1:248), where five-times reduction (or 0.7 log) was observed. When adhesion to tissue derived from pigsʹ jejunum was tested, concentration of E. coli was constant (6.9 ± 0.14 × 107 cfu/ml), while the concentration of Lb. gasseri K7 was 5.9 × 107 and 1.3 × 107 cfu/ml in two independent experiments, respectively. The adhesion of E. coli and Lb. gasseri K7 cells to jejunal mucosa was similar (1.0 ± 0.17 × 106 and 1.54 ± 0.10 × 106 cfu/cm2) when the concentrations of single strains in suspensions were approximately the same. No significant competition, exclusion or displacement of E. coli by lactobacilli was observed on jejunal tissue. In conclusion, Lb. gasseri K7 was found to be effective in reducing E. coli adhesion to Caco-2 enterocytes, but it was not able to do so in ex vivo conditions tested for pig jejunal tissue.