FACTORS INVOLVED IN ADHERENCE OF LACTOBACILLI TO HUMAN CACO-2 CELLS

A quantitative assay performed with bacterial cells labelled with [H-3]thymidine was used to investigate factors involved in the adherence of human isolates Lactobacillus acidophilus BG2FO4 and NCFM/N2, and Lactobacillus gasseri ADH to human Caco-2 intestinal cells. For all three Strains, adherence was concentration dependent, greater at acidic pH values, and significantly greater than adherence of a control dairy isolate, Lactobacillus delbrueckii subsp. bulgaricus 1489. Adherence of L. acidophilus BG2FO4 and NCFM/N2 was decreased by protease treatment of the bacterial cells, whereas adherence of L. gasseri ADH either was not affected or was enhanced by protease treatment. Putative surface layer proteins were identified on L. acidophilus BG2FO4 and NCFM/N2 cells but were not involved in adherence. Periodate oxidation of bacterial cell surface carbohydrates significantly reduced adherence of L. gasseri ADH, moderately reduced adherence oft. acidophilus BG2FO4, and had;no effect on adherence oft. acidophilus NCFM/N2. These results indicate that Lactobacillus species adhere to human intestinal cells via mechanisms which involve different, combinations of carbohydrate and protein factors on the bacterial cell surface. The involvement of a secreted bridging protein, which has been proposed as the primary mediator of adherence of L. acidophilus BG2FO4 in spent culture supernatant (M.-H. Coconnier, T. R. Klaenhammer, S. Kerneis, M.-F. Bernet, and A L. Servin, Appl. Environ. Microbiol. 58:2034-2039, 1992), was not confirmed in this study. Rather, a pH effect on Caco-2 cells contributed significantly to the adherence of this strain in spent culture supernatant. Our results indicate that adherence assays with Caco-2 cells should be performed under neutral-pH conditions to better mimic the intestinal environment and minimize acid effects that may artificially increase adherence.