Identification and distribution of the enterohemorrhagic Escherichia coli factor for adherence (efa1) gene in sorbitol- fermenting Escherichia coli O157 : H−

Abstract

AbstractSorbitol-fermenting (SF) Shiga toxin (Stx)-producing Escherichia coli (STEC) O157 : H− strains are emerging as causes of hemorrhagic colitis and the hemolytic-uremic syndrome in Europe. Using subtractive hybridization between SF STEC O157 : H− strain 493/89 and STEC O157 : H7 strain EDL933, three different fragments, of approximately 700 bp in length, were identified. Each demonstrated >99% homology to genes encoding the enterohemorrhagic E. coli factor for adherence (efa1) and lymphostatin (lifA). Therefore, a cosmid library was constructed from SF STEC O157 : H− strain 493/89, and one clone containing these fragments was sequenced. This sequencing demonstrated a 9669-bp open reading frame (ORF) that had 99.9% sequence homology to efa1 of STEC O111 : H− strain E45035 and to lifA of an enteropathogenic E. coli O127 : H6 strain E2348/69. In STEC O157 : H7 strain EDL933, only small (ca. 3 kb) initial and terminal fragments of this ORF are present. PCR analysis with primers complementary to the efa1/lifA sequence of strain 493/89 indicated that the complete sequence is present in each of 10 SF STEC O157 : H− isolates but in none of 10 STEC O157 : H7 strains investigated. The presence of the complete efa1/lifA also in both tested E. coli O55 : H7 strains supports the hypothesis that SF STEC O157 : H− are phylogenetically closer to the proposed E. coli O55 : H7 ancestor than STEC O157 : H7. Our data demonstrate the presence of a potential virulence gene in SF STEC O157 : H− that is only rudimentarily present in STEC O157 : H7.