This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Google Scholar Articles by Zheng, J. Articles by Meng, J. PubMed PubMed Citation Articles by Zheng, J. Articles by Meng, J. Agricola Articles by Zheng, J. Articles by Meng, J.

 Previous Article  |  Next Article 

Appl. Environ. Microbiol. doi:10.1128/AEM.00503-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification and Characterization of Shiga Toxin Type 2 Variants in Escherichia coli Isolated from Animals, Food, and Humans

Department of Nutrition & Food Science, University of Maryland, College Park, MD 20742; Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814; Center for Veterinary Medicine, Office of Research, Food & Drug Administration, Laurel, MD 20708

^* To whom correspondence should be addressed. Email: jmeng{at}umd.edu.

	Abstract

Considerable heterogeneity exists among the Shiga toxin (Stx) type 2 toxins elaborated by Shiga toxin-producing Escherichia coli (STEC). One such Stx2 variant, the Stx2d mucus-activatable toxin (Stx2dact), is rendered more toxic by the action of elastase present in intestinal mucus that cleaves the last two amino acids of the A2 portion of the toxin A subunit. We screened 153 isolates of STEC from food, animals, and humans for the gene encoding Stx2dact by a novel one-step PCR procedure. This method targeted the region of stx_2dact that encodes the elastase recognition site. The presence of stx_2dact was confirmed by DNA sequencing of the complete toxin genes. Seven STEC isolates from cows (4), meat (2), or a human (1) that carried putative stx_2dact were identified; all were eae-negative, and none were of the O157:H7 serotype. Three of the isolates (CVM9322, CVM9557, and CVM9584) also had stx₁, two (P1332 and P1334) had stx₁ and stx_2c and one (CL-15) had stx_2c. One isolate, P1130, harbored only stx_2dact. Vero cell cytotoxicity of supernatants from P1130 and the stx₁deletion mutants of CVM9322, CVM9557, and CVM9584 was increased 13- to 30- fold after treatment with porcine elastase. Thus, Stx2dact–producing strains, as detected by our one-step PCR method, can be isolated not only from humans, as previously documented, but also from food and animals. This latter finding has important public health implications based on a recent report from Europe of a link between disease severity and infection with STEC that produce the mucus activatable Stx2d.