The role of flagella, but not fimbriae, in the adherence of Salmonella enterica serotype Enteritidis to chick gut explant

To gain an understanding of the role of fimbriae and flagella in the adhere nce and colonisation of Salmonella enterica serotype Enteritidis in chicken s, an in-vitro gut adherence assay was developed and used to assess the adh erence of a wild-type Enteritidis strain and isogenic non-fimbriate and non -flagellate mutant strains. Enteritidis strain S1400/94, a clinical isolate virulent in chickens, was shown to possess genes which encoded type 1, SEF 14, SEF17, plasmid-encoded and long polar fimbriae. Mutant strains unable t o elaborate these fimbriae were created by allelic exchange. Each fimbrial operon was inactivated by the insertion of an antibiotic resistance gene ca ssette. In addition, fliC, motAB and cheA loci, which encode the major subu nit of the flagellum, the energy-translation system for motility and one of the chemotaxis signalling proteins, respectively, were similarly inactivat ed. Non-flagellate mutant strains were significantly less adherent than the wild-type strain, whereas mutant strains defective for the elaboration of any of the types of fimbriae adhered as well as the wild-type strain. A fla gellate but non-motile (paralysed) mutant strain and a smooth-swimming chem otaxis-deficient mutant strain were shown to be less adherent than the wild -type strain, but that observation depended on the assay conditions used.