CHARACTERIZATION OF A PHAGE SPECIFIC TO HEMORRHAGIC ESCHERICHIA-COLI O157-H7 AND DISCLOSURE OF VARIATIONS IN HOST OUTER-MEMBRANE PROTEIN OMPC

Phage AR1, previously known to infect Escherichia coli 0157:H7 with hi gh specificity, was further characterized for its genetic properties. The phage DNA sequences including capsid genes and a putative alpha-gl ucosyltransferase gene (alpha-gt) have been deduced. These sequences a re conservative but not identical to those of T4 phage, However, a non essential gene, SegD, organized within the capsid gene cluster of T4 i s missing in the corresponding region of AR1 genome, and this characte ristic has not been observed among T-even related phages. The differen ce between AR1 and T4 was further exemplified by their distinct host r anges. Strains of E. coli 0157:H7 collected from different sources wer e permissive to AR1 but resistant to T4 that normally infects K-12 str ains off, coli through contact with the outer membrane protein OmpC. T hus, the 0157:H7 strains must have a varied OmpC, Indeed, the OmpC seq uence of 0157:H7 strains was proved to differ from that of K-12 strain s by a total of 15 amino acid substitutions and two gaps (a five-resid ue deletion and a four-residue insertion). The OmpC molecules are rela tively conserved across the gram-negative bacteria, and this is the fi rst time OmpC divergence has been found within the same E, coli specie s. Since OmpC is located in the outer membrane and its expression is r egulated by environmental conditions, alteration of the structure in p athogenic 0157:H7 strains may have biological significance.