The role of fimbriae and flagella in the adherence of avian strains of Escherichia coli O78 : K80 to tissue culture cells and tracheal and gut explants

To investigate the role of fimbriae and flagella in the pathogenesis of avi an colibacillosis, isogenic insertionally inactivated mutant strains of Esc herichia coil O78:K80 strain EC34195 defective in the elaboration of type-1 and curli fimbriae and flagella were constructed by allelic exchange, Sing le and multiple non-fimbriate and non-flagellate mutant strains were compar ed to the wild-type in vitro in adherence assays with a HEp-2 cell line, a mucus-secreting cell line HT2916E, a non-mucus-secreting cell line HT2919A, tracheal explant and proximal gut explant, Mutant strains defective in the elaboration of type-1 fimbriae were significantly less adherent - in the o rder of 90% reduction - than the wild-type strain in all assays. Mutant str ains defective in the elaboration of flagella were generally as adherent as the wild-type strain except when assayed with the mucus-secreting cell lin e HT2916E, for which a significant reduction of adherence - of the order of 90% - compared with the wild-type strain was observed. Mutant strains defe ctive for the elaboration of curb fimbriae adhered as well as the wild-type strain in all assays, except when assayed in tests with gut explant tissue for which a significant reduction of adherence - of the order of 80% - com pared with the wild-type strain was observed, Adherence to explants was to epithelial, not serous, surfaces and was 10-fold greater to tracheal than t o gut explants, Together, these data support the hypothesis that type-1 fim briae are significant factors in adherence, aided by flagella for penetrati on of mucus and curli fimbriae for adherence to the gut.