International Journal of Food Microbiology 45 (1998) 229–235 Short Communication Virulence genes of Shiga toxin-producing Escherichia coli isolated from food, animals and humans a, 1 ,a b * Jianghong Meng , Shaohua Zhao , Michael P. Doyle a Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, USA b The Center for Food Safety and Quality Enhancement and Department of Food Science and Technology, University of Georgia, Griffin, GA 30223, USA Received 22 January 1998; received in revised form 3 September 1998; accepted 25 September 1998 Abstract The presence of virulence genes, encoding enterohemorrhagic Escherichia coli (EHEC)-hemolysin (EHEC-hlyA), intimin ( eae), and Shiga toxins 1 ( stx1) and 2 ( stx2), in 178 isolates of pathogenic E. coli, was determined using the polymerase chain reaction with primers specific for each virulence gene. The tested organisms were 120 isolates of E. coli O157:H7 from human patients, cattle, sheep and foods, 16 non-O157:H7 EHEC isolates from patients suffering from hemorrhagic colitis or hemolytic uremic syndrome, 15 non-O157:H7 Shiga toxin-producing E. coli (STEC) isolates from cattle and foods, 26 isolates of enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC) and enterotoxigenic E. coli (ETEC), and an E. coli K12 strain. Results revealed that all isolates of O157:H7 carried EHEC-hlyA, eae, and one or both stx genes; 15 of the 16 non-O157:H7 EHEC isolates had EHEC-hlyA, but all possessed eae and one or both stx genes; only seven of the 15 non-O157 STEC isolated from cattle and foods contained both EHEC-hlyA and eae genes. The EPEC, EIEC, ETEC, and the E. coli K12 strain did not carry these virulence genes, except eight EPEC isolates were positive for eae. Results suggest that a combination of EHEC-hlyA and eae genes could serve as markers to differentiate EHEC from less pathogenic STEC, and other pathogenic or non-pathogenic E. coli.  1998 Elsevier Science B.V. All rights reserved. Keywords: Escherichia coli ; Shiga toxin; Virulence genes 1. Introduction when E. coli O157:H7 caused two outbreaks of hemorrhagic colitis associated with consumption of Shiga-toxin producing Escherichia coli (STEC) undercooked ground beef (Doyle and Padhye, 1989; were first recognized as human pathogens in 1982 Griffin, 1995; Doyle et al., 1997). Since then, more than 100 serotypes of STEC have been isolated from * Corresponding author. Tel.: 1 1-301-405-1399; fax: 1 1-301- animals, food and other sources. Most outbreaks of 314-9327; e-mail: jm332@umail.umd.edu 1 STEC in North America and Europe have been Present address: Division of Animal Research, Office of Re- associated with serotype O157:H7 (Griffin, 1995; search, Center for Veterinary Medicine, Food and Drug Adminis- tration, Laural, MD 20708, USA. Thomas et al., 1996), but several were caused by 0168-1605 / 98 / $ – see front matter  1998 Elsevier Science B.V. All rights reserved. PII: S0168-1605(98)00163-9