Novel type of fimbriae encoded by the large plasmid of sorbitol-fermentingenterohemorrhagic Escherichia coli O157 : H-

Sorbitol-fermenting (SF) enterohemorrhagic Escherichia coli (EHEC) O157:H- have emerged as important causes of diarrheal diseases and the hemolytic-ur emic syndrome in Germany. In this study, we characterized a 32-kb fragment of the plasmid of SF EHEC O157:H-, pSFO157, which differs markedly from pla smid pO157 of classical non-sorbitol-fermenting EHEC O157:H7, We found a cl uster of six genes, termed sfgA, sfpH, sfpC, sfpD, sfpJ, and sfpG, which me diate mannose-resistant hemagglutination and the expression of fimbriae. sf p genes are similar to the pag genes, encoding P-fimbriae of uropathogenic E. coli, but the sfg cluster lacks homologues of genes encoding subunits of a tip fibrillum as well as regulatory genes, The major pilin, SfpA, despit e its similarity to PapA, does not cluster together with known PapA alleles in a phylogenetic tree but is structurally related to the PmpA pilin of Pr oteus mirabilis. The putative adhesin gene sfpG, responsible for the hemagg lutination phenotype, shows significant homology neither to papG nor to oth er known sequences. Sfp fimbriae are 3 to 5 nm in diameter, in contrast to P-fimbriae, which are 7 nm in diameter, PCR analyses showed that the sfp ge ne cluster is a characteristic of SF EHEC O157:H- strains and is not presen t in other EHEC isolates, diarrheagenic E. coli, or other Enterobacteriacea e. The sfp gene cluster is Ranked by two blocks of insertion sequences and an origin of plasmid replication, indicating that horizontal gene transfer may have contributed to the presence of Sfp fimbriae in SF EHEC O157:H-.