Characterization of a Phage Specific to Hemorrhagic <i>Escherichia coli&nbsp; </i>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.

T4-Like Genome Organization of the Escherichia coli O157:H7 Lytic Phage AR1

“…Similar to the case with T4 and other T4-like phages, restric-tion enzyme digestion experiments suggested that the AR1 genome is highly modified to protect it from restriction enzyme digestion by the host defense system (89). Partial sequencing data (ϳ10 kb) of AR1 indicated that AR1 has several structural genes that are highly similar to T4 genes (17,37,89).…”

“…All of the E. coli strains were cultured at 37°C in Luria-Bertani broth with agitation (180 rpm). AR1 phage were propagated in E. coli O157:H7 strain 1266 as described previously (70,89). E. coli phages T4 and RB69, obtained from J. D. Karam (Tulane University), were propagated in E. coli strain B E (92).…”

“…A previous study suggested that the putative AR1 gp37 receptor recognition protein may recognize and bind to the OmpC receptor because an E. coli O157:H7 OmpC disruption mutation rendered the cell resistant to AR1 infection (90). Similar to the case with T4 and other T4-like phages, restric-tion enzyme digestion experiments suggested that the AR1 genome is highly modified to protect it from restriction enzyme digestion by the host defense system (89). Partial sequencing data (ϳ10 kb) of AR1 indicated that AR1 has several structural genes that are highly similar to T4 genes (17,37,89).…”

“…It has a typical T4-like virion morphology under a transmission electron microscope. AR1 has a wide host range (17,89) and can efficiently infect and lyse both Shiga toxin-producing E. coli (STEC) and E. coli collection of reference (ECOR) strains but not the E. coli K-12 or B E strains. In addition, AR1 can also lyse other Enterobacteriaceae bacteria, such as Shigella dysenteriae and Salmonella enterica subsp.…”

“…In addition, AR1 can also lyse other Enterobacteriaceae bacteria, such as Shigella dysenteriae and Salmonella enterica subsp. enterica serovars Choleraesuis and Enteritidis (17,89). Host range receptor assays (17) showed that AR1 uses the R1, R3, and R4 core oligosaccharide (OS) types of lipopolysaccharide (LPS), but not the R2 or K-12 type, as cellular receptors (17).…”