ABSTRACT
S fimbriae have the capacity to agglutinate human and bovine erythrocytes. F1C, another type of fimbriae, was described as a nonhemagglutinating adherence factor. Fimbriae of the S/F1C super family have been analyzed by electron microscopy. They represent rod-like structures of 1 to 2 tim length and a diameter of approximately 7 nm. S fimbriae bind with high affinity to receptors, comprising the sugar sequence sialic acid a 2-3 lactose. The protein sequences of the fimbrial subunit proteins of S fimbriae of the urinary tract infections strain 536, the meningitis isolate IHE 3034, and those of F1C fimbriae were established on the basis of their nucleotide sequences. The introduction of seven site-directed mutations in the sfaS sequence made it possible to identify an epitope involved in binding of the sialic acid-specific adhesin. Mutations in sfaB or sfaC demonstrated that both gene products were indispensable for effective sfa expression from the wild-type gene cluster.
