Construction and characterization of type 1 non-fimbriate and non-adhesive mutants of Salmonella typhimurium.

Mutations in the fimH gene of Salmonella typhimurium result in a non-fimbriate, non-adhesive phenotype. This phenotype was shown to be due to the lack of both fimH and fimF expression since disruption of the fimH gene by insertion of a DNA cassette into this determinant results in mutants that are complemented by plasmids carrying both fimH and fimF. Deletion mutations within the S. typhimurium fimH gene carried on a recombinant plasmid can be used to complement the mutant, and these transformants are non-adhesive but fully fimbriate, consistent with the role of FimH as being necessary for fimbrial adhesin expression. Adherence to erythrocytes, HeLa, and Hep-2 cells is associated with expression of the FimH polypeptide, and fimbriate strains that cannot synthesize FimH are non-adhesive. Discrete differences in the amino acid sequences of the adhesive type 1 and the non-hemagglutinating type 2 FimH polypeptides were detected, and are most likely responsible for the differences in hemagglutinating activity.