Purpose: To evaluate the effect of GI transit on the bacterial adhesion to enterocyte cell line (Caco-2).
Methods: Caco-2 cells were cultured in DMEM, seeded onto Transwell membrane and incubated to allow the formation of differentiated monolayer. Pathogens were adapted to in vitro GI environment: a 1-h in vitro gastric digestion process followed by an intestinal digestion of 1 h. Adapted bacteria (8 log CFU/ml) were transferred to cell monolayer (MOI 100:1) and incubated for 1 h. Caco-2 were washed with PBS to remove non-adherent bacteria, and treated with Triton-X100 to dissociate adherent bacteria, which were then counted. The % adhesion (adherent bacteria divided by total bacteria × 100) for adapted and intact bacteria was compared.
Results: Three avian clinical strains Escherichia coli Tk301:k1 and O78:H80 and Salmonella enterica var. Typhimurium DT104 were tested. The overall % adhesion (1.06 ± 0.82%) varied greatly among strains and test days (range 0.33 to 3.1%). For all strains, bacterial adhesion with and without in vitro GI transit treatment did not differ significantly.
Significance: Although bacterial adaptation to GI environment can induce the expression of adhesins and other bacterial surface components, this did not improve early adhesion of pathogens. This suggests that adhesins and other specific surface proteins do not play significant role during the initial stage of adhesion. Initial contact between bacteria and cells appears to be mainly non-specific and dependent on the hydrophobicity and surface charge of bacterial cells.