The routine use of antibiotics in modern poultry farming practices has contributed to the rise of antibiotic resistance, posing a risk to human health through the transfer and spread of resistant bacteria and genes across different sectors. This study aimed to investigate the carriage of antibiotic-resistant bacteria in healthy broiler chickens in Pakistan. A total of 151 chicken cloacal swab samples were collected from different poultry farms and retailers' shops in the district of Rawalpindi, Pakistan. The samples were inoculated on the growth media with and without antibiotics (cefotaxime, meropenem, ciprofloxacin, colistin) for selection of resistant organisms. Antibiotic sensitivity tests were performed for a subset of isolates from non-antibiotic plates following Clinical and Laboratory Standards Institute (CLSI) guidelines 2025. Single, multiplex and enterobacterial repetitive intergenic consensus PCRs were carried out to screen the resistance genes, phylogroups and types of Escherichia coli ( E. coli ). From 151 cloacal swabs, 1505 isolates were recovered where E. coli was the most prevalent (66.7%, 1008/1505), followed by Pseudomonas aeruginosa ( P. aeruginosa , 233/1505, 15.48%), Klebsiella pneumoniae ( K. pneumoniae, 17/1505, 1.12%) and Citrobacter spp. (24/1505, 1.59%), Staphylococcus aureus ( n = 216/1505, 1.35%), and Staphylococcus epidermidis ( n = 7/1505, 0.46%). In 313 E. coli on plates containing cefotaxime, we found a higher level of bla TEM (19.69%, n = 62) followed by bla CTX-M (14.64%, n = 46), and bla SHV (1.59%, n = 5). In 231 E. coli on meropenem plates, bla OXA-48 was detected in 2 (0.86%) isolates. The plasmid-mediated quinolone-resistance genes were also identified in E. coli , and qnr S (12.71%, n = 15/118) was more prevalent than qnr B (2.54%, n = 3/118). In 88 P. aeruginosa on cefotaxime plates , bla TEM (6.81%, n = 6) was more prevalent, followed by bla SHV (4.54%, n = 4), and bla CTX-M (3.40%, n = 3). In 46 P. aeruginosa on meropenem plates, only one isolate had bla OXA-48. Colistin resistance gene, mcr- 1, was more prevalent in E. coli (77.7%, n = 129/166), followed by P. aeruginosa (17.64%, n = 6/34). Phylogrouping of 105 E. coli isolates showed 19% isolates belonging to Group E/Clade I, and 18.1% in Group B1. Group A had 13.3% isolates, group D/ E had 10.5% isolates, group F had 3.8% isolates, group A/C and Clade I/II had 2.8% isolates each, and one isolate in group B2. The presence of antibiotic-resistant bacteria in healthy chickens is a significant public health concern and reflects inappropriate antimicrobial use in the poultry and animal sector. Poultry may serve as an important reservoir for the transmission of resistant bacteria between humans and the environment.
Ali et al. (Tue,) studied this question.
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