Comparative pathogenicity, toxicity and pulse types of o157 and non -o157 escherichia coli

Shiga toxin producing Escherichia coli (STEC) are recognized as an important foodborne pathogen, responsible for sporadic cases to serious outbreaks worldwide (Wani et al., 2003). The morbidity and mortality associated with several recent outbreaks due to STEC have highlighted the threat this organism poses to global public health. The present study describes the molecular characterization of STEC expressing five different serotypes (O157, O158, O114, O125 and O26) isolated from different sources in Egypt and investigates their clonal relationship. The present study investigated the ability of each Shiga toxin producing strains with different genetic backgrounds to induce disease in vivo using a rat model. STEC strains were identified and characterized by PCR and DNA sequencing analysis; clonality was determined by comparing pulsetypes generated during pulsed field gel electrophoresis. Ten STEC isolates (three from human stool, four from animal stool, two from meat products and one from untreated water) were positive for a combination of stx genes; three were positive for both stx1 and stx2, the remaining were only positive for stx1. Two of the STEC isolates contained eae, whereas one carried the enterohemorrhagic E. coli (EHEC) hemolysin gene, hlyA. All STEC isolates exhibited in vivo toxic effects after inoculation of STEC bacterial broth or their respective purified toxin to experimental rats. Subtyping of the ten STEC isolates by pulsed-field gel electrophoresis (PFGE) revealed three distinct restriction patterns. Sixty percent (6/10) of the isolates shared the same PFGE (mrp1) pattern, representing the most common profile; and 30% (3/10) shared a second common (mrp II) pattern. Only one strain (10%) showed a distinct and unique mrp III PFGE profile. In vivo challenge experiments with O157 and non O157 STEC induced disease in rats, including pronounced epithelial lesions and severe vascular damage. This study identified STEC O157 from human cases with diarrhea, and demonstrated that meats and untreated water available in Egypt were contaminated with diverse non-O157 STEC strains. This finding is of concern due to the potential of these organisms to cause human disease.