F-17-LIKE FIMBRIAE FROM AN INVASIVE ESCHERICHIA-COLI STRAIN PRODUCINGCYTOTOXIC NECROTIZING FACTOR TYPE-2 TOXIN

The F17b fimbriae encoded by the transmissible virulence plasmid Vir, also coding for cytotoxic necrotizing factor type 2, were characterize d. A 5.7-kb region of Vir mediates in vitro N-acetylglucosamine-sensit ive adhesion to calf intestinal villi. Sequence analysis revealed that this region codes for a structural subunit and an adhesin closely rel ated to the F17-A and F17-G proteins encoded by the F17 fimbrial gene cluster. The F17b-A gene presents an open reading frame of 540 bp enco ding a polypeptide of 180 amino acids with a putative signal peptide o f 21 residues. The mature protein shows an identity of 74% with the F1 7-A structural subunit. This 20-kDa protein is recognized by antiserum directed against F17 fimbriae. The F17b-G gene shows an open reading frame of 1,029 bp encoding a polypeptide of 343 amino acids with a put ative signal peptide of 22 residues. The F17b G polypeptide exhibits 9 5% identity with the F17-G adhesin. The functional homology of the gen e products was further confirmed by demonstrating that mutants in the F17-A gene can be complemented by the F17b-A gene and vice versa. Thes e results prove that fimbriae belonging to the F17 family are also fou nd on pathogenic Escherichia coli strains other than enterotoxigenic i solates producing heat-labile or heat-stable enterotoxin.