Accession Number:

ADA421553

Title:

The Regulation of Expression of the Stx2d Toxins in Shiga Toxin-producing Escherichia coli O91:H21 Strain B2F1

Descriptive Note:

Doctoral's thesis

Corporate Author:

UNIFORMED SERVICES UNIV OF THE HEALTH SCIENCES BETHESDA MD

Personal Author(s):

Report Date:

2002-01-01

Pagination or Media Count:

153.0

Abstract:

Shiga toxin Stx types 1 and 2 are encoded within intact or defective temperate bacteriophages in Stx-producing Escherichia coli STEC, and expression of these toxins is linked to bacteriophage induction. Among Stx2 variants, only stx2e from one human STEC isolate has been reported to be encoded within a toxin-converting phage. In this study, I examined O91H21 STEC isolate B2F1 that carries two functional alleles stx2d1 and stx2d2 for the potent activatable Stx2 variant toxin, Stx2d, for the presence of Stx2d converting bacteriophages and other potential regulators of toxin expression. Mutants of B2F1 that produced one or the other Stx2d toxin were made. The Stx2d1-producing mutant stx2d2cat was less cytotoxic for Vero cells than the Stx2d2-producing mutant stx2d1cat. Consistent with those results, the Stx2d1-producing mutant was attenuated in a streptomycin-treated mouse model of STEC infection, while the Stx2d2-producing mutant was nearly as virulent as wild-type B2F1. When the mutants were treated with mitomycin C to promote bacteriophage induction, Vero cell cytotoxicity was elevated only in extracts of the Stx2d1-producing mutant. Additionally, when mice were treated with ciprofloxacin, an antibiotic that induces the O157H7 Stx2-converting phage, the animals were more susceptible to the Stx2d1-producing mutant. An stx2d1-containing lysogen was isolated from plaques on strain DH5945 that had been exposed to lysates of the mutant that produced Stx2d1 only. However, that RecA- lysogen could not be induced for phage nor were culture lysates from it cytotoxic for Vero cells. By contrast, when the lysogen was transformed with a plasmid encoding RecA and induced with mitomycin C, culture extracts were cytotoxic for Vero cells. Furthermore, electron microscopic examination of extracts from the 966B2F1-lysogen showed hexagonal particles that r

Subject Categories:

  • Medicine and Medical Research
  • Microbiology

Distribution Statement:

APPROVED FOR PUBLIC RELEASE