Characterization of a Phage Specific to Hemorrhagic Escherichia coli O157:H7 and Disclosure of Variations in Host Outer Membrane Protein OmpC

Abstract

Phage AR1, previously known to infect Escherichia coli O157:H7 with high specificity, was further characterized for its genetic properties. The phage DNA sequences including capsid genes and a putative α-glucosyltransferase gene (α-gt) have been deduced. These sequences are conservative but not identical to those of T4 phage. However, a nonessential gene, SegD, organized within the capsid gene cluster of T4 is missing in the corresponding region of AR1 genome, and this characteristic has not been observed among T-even related phages. The difference between AR1 and T4 was further exemplified by their distinct host ranges. Strains of E. coli O157:H7 collected from different sources were permissive to AR1 but resistant to T4 that normally infects K-12 strains of E. coli through contact with the outer membrane protein OmpC. Thus, the O157:H7 strains must have a varied OmpC. Indeed, the OmpC sequence of O157:H7 strains was proved to differ from that of K-12 strains by a total of 15 amino acid substitutions and two gaps (a five-residue deletion and a four-residue insertion). The OmpC molecules are relatively conserved across the gram-negative bacteria, and this is the first time OmpC divergence has been found within the same E. coli species. Since OmpC is located in the outer membrane and its expression is regulated by environmental conditions, alteration of the structure in pathogenic O157:H7 strains may have biological significance.