Antibiotic Resistance and Virulence Gene Patterns Associated with Multi Drug Resistant Avian Pathogenic Escherichia coli (APEC) Isolated from Broiler Chickens in India

In the present study, a total of 102 samples were collected from chickens of different flocks, died due to suspected colibacillosis. Bacteriological and PCR methods were applied to detect avian pathogenic Escherichia coli (APEC). Phenotypic antimicrobial resistance (AMR) was determined by disk diffusion method. Extended spectrum beta lactamases (ESBL) detection was carried out via PCR by targeting bla TEM, bla SHV, blaOXA, and bla CTX-M groups 1, 2, and 9. Genes of eight virulence factors and class I integrons were also detected by PCR using gene specific primers. Culture, microscopic, biochemical tests and PCR recognised 69/102 (67.64%) samples as E. coli . Phenotypic AST revealed higher resistance against fluoroquinolone antibiotics, i.e ., enrofloxacin (72.46%), levofloxacin (69.56%) & ciprofloxacin (66.66%), followed by amoxyclav (63.77%) and tetracycline (59.42%). Six isolates were found as pan-drug-resistant E. coli . A total of 48 (69.56%) and 7 (10.14%) isolates were positive for the presence of bla TEM and bla CTX-M-G9 genes, respectively, whereas 2 (2.90%) isolates each were found positive for bla SHV, blaOXA, and bla CTX-M-G1 genes. Among APEC associated virulence genes, iss (79.71%) was the most predominant, followed by tsh (50.72%), ast (30.43%), cvaf (26.08%), pap (23.18%), vat (8.69%) and stx -1 (1.44%). Thirty-two isolates harboured class I integrons, either with or without ESBL genes. Conclusively, the isolates under study showed pan and multiple-drug resistance, specifically against fluoroquinolone drugs. ESBL production was mediated principally through bla TEM and bla CTX-M-G9. Multiple virulence factors, toxins, and carriage & spread factor render these as zoonotically potential pathogens for humans.