Virulence Genes, Antibiotic Resistance and Phylotyping of Escherichia coli O157 Recovered from Diarrheic Calves

E. coli O157 is one of the main food-borne pathogens that attributed to the attaching and effacing Shigatoxigenic E. coli pathotype (AE-STEC). The occurrence of E. coli O157 in diarrheic calves investigated through molecular detection of rfbEO157 encoding gene was 8.02% within E. coli strains. Detection of AE-STEC virulence genes in E. coli O157 strains using multiplex PCR showed the presence of eae, stx1, stx2 and ehylA in percentages of 93.3, 73.3, 20 and 13.3%, respectively. The virulence genes profile of E. coli O157 revealed the predominance of eae+stx1 combination in 66.7% of these strains. All E. coli O157 strains exhibited antibiotic multi-resistances with higher resistance (100%) to amoxicillin/clavulanic acid, cefalexin, cefuroxime and tetracycline, while the lowest resistance was detected for gentamicin (40%). Phenotypic resistance to extended spectrum cephalosporins (ESCs) indicated that 60% of these strains were resistant to ceftriaxone and cefotaxime, while 53.3% were resistant to cefquinome. Molecular detection of extended spectrum β-lactamases (ESBLs) encoding genes recorded the superiority of blaTEM gene (100%), whereas the blaSHV and blaCTXM genes were detected in percentages of 40 and 20%, respectively. The genetic profiling of resistance genes revealed the role of blaCTXM gene in ESCs resistance as blaTEM+blaSHV+blaCTXM combination was detected only in ESC resistant strains. Finally, B2 phylogroup was the most prevalent one (80%) within E. coli O157 strains. This implicates diarrheic calves as a source of highly pathogenic multi-resistant E. coli O157 strains.