Molecular analysis of ESBL- and AmpC-producing Enterobacteriaceae in fecal samples from broiler and backyard chickens

To analyse the molecular profile of antibiotic resistance in Enterobacteriaceae isolates from fecal samples of healthy broilers and backyard chickens in Tamil Nadu, India. A total of 115 and 57 bacterial strains were isolated from fecal samples of broiler and backyard chickens respectively using conventional bacterial culture tests. Bacterial isolates were screened for antibiotic susceptibility by Kirby-Bauer's disk diffusion method. Colistin susceptibility was tested using the broth microdilution method. Extended-spectrum β-lactamase (ESBL), AmpC β-lactamase and metallo-β-lactamase (MBL) producers were screened by combination disk method. The drug-resistant genes' positivity was analysed by polymerase chain reaction (PCR) method. Escherichia coli was the predominant bacterium isolated from both broiler (53%) and backyard (64.9%) chickens. Bacterial isolates from broilers and backyard chickens showed 100% resistance to ampicillin, piperacillin, and piperacillin-tazobactam. Five bacterial isolates from broiler chickens were resistant to colistin. ESBL producers were 34.7% in broilers and 19.1% in backyard chickens. AmpC production was detected in 44.3% of the isolates from broilers and 26.2% of those from backyard chickens. Molecular analysis revealed that bacterial isolates from broiler chickens tested positive for drug-resistant genes such as blaTEM (25%), blaSHV (5%), blaCTX-M (4%), blaAmpC (56%), integron (39%), sul1 (30%), and sul2 (23%). Bacterial isolates from backyard chickens tested positive for the blaTEM (22%), blaSHV (14%), blaAmpC (54.3%), and integron (20%) genes. None of the isolates from either a broiler or backyard chickens harboured New Delhi metallo-β-lactamase (blaNDM) or colistin-resistant genes (mcr-1 to −3). Bacterial isolates from broiler chickens harboured a higher number of drug resistance genes, especially blaTEM, blaCTX-M, sul1, sul2, and integron, than those from backyard chickens.