Characterization of enterohemorrhagic Escherichia coli from diarrhoeic patients with particular reference to production of Shiga-like toxin.

Enterohemorrhagic Escherichia coli (EHEC) is a subtype of pathogenic E. coli that causes diarrhea or hemorrhagic colitis in humans, which can progresses to hemolytic uremic syndrome (HUS), a leading cause of acute renal failure in children, and morbidity and mortality in adults. Stool samples (n = 273) of patients (1 day-40 years old) suffered from bloody diarrhea and abdominal cramps, were examined bacteriologically and molecularly for the presence and pathogenicity of EHEC with phylogenetic analysis of the obtained stx1, stx2, and eaeA virulence genes' sequences. Overall, 71 (26.01%) E. coli isolates were identified as EHEC with the following serogroupes: O1:H11 (3), O128:H2 (9), O26:H11 (6), O157:H7 (3), O25:H2 (7), O145:H328 (2), O125:H6 (9), O86:H8 (5), O18:H15 (11) and untypable (16). The highest isolation rate were in samples belonged to infants below two years old (42.25%). Antimicrobial susceptibility testing showed that all isolates were highly sensitive to ciprofloxacin, nitrofurantoin, gentamycin, imipenem and vancomycin (100% each), however, they were resistant to ampicillin, cephalexin, penicillin and tetracycline (100% each). In-vitro pathogenicity testing of the isolates revealed that 67 (94.37%) isolates were positive for Congo red test, 47 (66.20%) isolates possessed P fimbriae (MRHA) and 17 (23.94%) possessed type 1 fimbriae (MSHA). Moreover, 46 (64.79%) isolates exhibited hemolysis and 42 (59.15%) isolates showed distinct cytopathic effect to Vero cells. Molecular detection of enterohemorrhagic E. coli (EHEC) pathotype virulence genes, confirmed the presence of stx1 gene in O157:H7 (MA2), O26:H11, O145:H328 and O125:H6 serogroups; stx2 gene in (O157:H7 (MA1), O128:H2 and O25:H2; while all serogroups except (O125:H6) carried the eaeA intimin virulence gene. A phylogenetic tree, based on the nucleotide sequences of toxin-encoding genes, demonstrates that Shiga toxin E. coli (STEC) isolates have considerable genetic variation and belong to various phylogenetic groupings.