Two toxin-converting phages from Escherichia coli O157:H7 strain 933 encode antigenically distinct toxins with similar biologic activities

Abstract

Escherichia coli 0157:H7 strain 933 contains two distinct toxin-converting phages (933J and 933W). The biologic activities and antigenic relationship between the toxins produced by 933J and 933W lysogens of E. coli K-12, as well as the homology of the genes that encode the two toxins, were examined in this study. The 933J and 933W toxins, like Shiga toxin produced by Shigella dysenteriae type 1, were cytotoxic for the same cell lines, caused paralysis and death in mice, and caused fluid accumulation in rabbit ileal segments. The cytotoxic activity of 933J toxin for HeLa cells was neutralized by anti-Shiga toxin, whereas the activity of 933W toxin was not neutralized by this antiserum. In contrast, an antiserum prepared against E. coli K-12(933W) neutralized 933W toxin but not 933J toxin or Shiga toxin. For E. coli 933, most of the cell-associated cytotoxin was neutralized by anti-Shiga toxin, whereas most of the extracellular cytotoxin was neutralized by anti-933W toxin. However, a mixture of these antisera indicated the presence of both toxins in cell lysates and culture supernatants. Among 50 elevated cytotoxin-producing strains of E. coli, we identified 11 strains isolated from cases of diarrhea, hemorrhagic colitis, or hemolytic uremic syndrome that produced cell-associated cytotoxins which were neutralized by the 933W antitoxin. Southern hybridization studies showed that the cloned toxin structural genes from phage 933J hybridized with DNA from phage 933W under conditions estimated to allow no more than 26% base-pair mismatch. These findings indicate that E. coli produces two genetically related but antigenically distinct cytotoxins with similar biologic activities which we propose to name Shiga-like toxins I and II. Strains of E. coli that produce elevated levels of Shiga-like toxin I or Shiga-like toxin II, or both, have been associated with the clinical syndromes of diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome.

Inducible stx2 phages are lysogenized in the enteroaggregative and other phenotypic Escherichia coli O86:HNM isolated from patients

“…Genotypic and phenotypic variations among stx-converting phages derived from O157 and non-O157 STEC have been repeatedly reported [11,18,24,25]. Our investigations also show the genotypic and phenotypic divergence of stx2-converting phages derived from not only O157 but also non-O157 STEC.…”

Toxins

“…Strains of Sh. dysenteriae 1 hybridize with DNA probes specific for VT1 gene sequences derived from a strain of E. coli, confirming the relatedness of VT1 and Shiga toxin (Strockbine et al 1986;Smith et al 1987b). There was no hybridization with a probe specific for VT2 gene sequences (Smith er a/.…”

“…A strain of E. coli 0157 producing VT1 only has since been identified (Smith et al 1987a). These toxins have also been termed SLTI and SLTII (Strockbine et al 1986).…”

“…VT production is phage-determined in a number of strains (Scotland et al 1983;Smith et al 1983;Strockbine et al 1986). In those studies where distinct VTs were identified it was shown that phages encoded VT1 or VT2 but not both toxins.…”

Highly conserved B-subunit genes of Shiga-like toxin II variants found in Escherichia coli O157 strains

“…This has resulted in subgrouping of SLT-II toxins. One subgroup includes the prototype SLT-II encoded by bacteriophage 933W [4] and several variants of SLT-II (i.e. SLT-IIvha (VT2vha), SLT-IIvhb (VT2vhb), SLT-IIvhc, SLT-IIc) which are about 97% related to SLT-II at the deduced amino acid level of the B-subunits while the A-subunits share 98-100% homology with SLT-IIA [5-7].…”