Distribution of antimicrobial resistance and some widespread extended-spectrum beta-lactamase genes in different phylogroups of Shiga toxin-producing Escherichia coli (STEC) isolates of ruminant origin

Limited data is available on the prevalence of extended-spectrum beta-lactamase (ESBL) genes in Shiga toxin-producing Escherichia coli (STEC) isolates of ruminant origin. This study determined the molecular prevalence of ESBL-encoding genes (blaCTX-M, blaTEM, blaSHV and blaOXA) and antimicrobial-resistance (AMR) of 58 STEC isolates recovered from cattle (n= 32), sheep and goats (n= 26). In the current study, ESBL genes were identified by the molecular technique, while phenotypic AMR against six antibiotics (amoxicillin-clavulanic acid, tetracycline, neomycin, florfenicol, enrofloxacin and sulfamethoxazole-trimethoprim) were tested by disc diffusion method. Phylogenetic groups were also determined by a PCR scheme. Isolates were categorized into five phylogroups (A, B1, C, D and E) and B1 was the most prevalent phylogenetic group (43; 74.1%). Statistical analysis revealed significant association between phylogroup D and small ruminants (sheep and goats, p= 0.014). Moreover, the highest rates of antimicrobial resistance were related to tetracycline (25.9%) and neomycin (22.4%). Resistant isolates to tetracycline (p= 0.001), trimethoprim-sulfamethoxazole (p= 0.013) and neomycin (p= 0.000) were significantly prevalent among strains recovered from cattle. In addition, the majority of MDR strains were also had a significant distribution among cattle isolates (p= 0.001). In the current study, prevalence of ESBL positive STEC was 12.06% (7/58). Genes blaCTX-M and blaTEM were detected separately and in combination in bovine isolates. However, only one STEC strain of small ruminants harbored blaTEM. In conclusion, it seems that cattle isolates are notable sources of different AMR traits which could be a threat to veterinary sections, public health and food hygiene, in particular.