Tissue-Site Distribution, Antimicrobial Resistance Profile, and Phenotypic ESBL Production of Escherichia coli Isolated from Retail Chicken Carcasses in Bharatpur Metropolitan City, Chitwan, Nepal.

Poultry meat is Nepal's most dynamic agricultural subsector, yet food safety remains a concern as retail carcasses are frequently contaminated by antimicrobial-resistant Escherichia coli. This cross-sectional study determined the tissue-site distribution, antimicrobial resistance profile, and phenotypic ESBL production of phenotypically identified E. coli isolated from 144 retail chicken carcasses collected from 16 randomly selected meat shops (9 carcasses per shop) in Bharatpur Metropolitan City, Chitwan, Nepal, sampling the liver, muscle, and skin of each bird. Of 432 tissue samples examined, 96 E. coli isolates were recovered, giving an overall tissue-level prevalence of 22.22% and a carcass-level prevalence of 40.97% (59/144; shop-cluster-adjusted 95% CI 29.4-53.6%). Isolation was highest from liver (34.72%), followed by muscle (21.53%) and skin (10.42%); the odds of isolation were 4.17 times higher in the liver than in muscle and 12.67 times higher in the liver than in skin (p<0.001). Susceptibility testing against seven antibiotics showed the highest resistance to nalidixic acid (82.29%) and tetracycline (71.88%), and the lowest resistance to ceftriaxone (12.50%). Multidrug resistance was detected in 91.67% (88/96; 95% CI 84.24-96.33%) extensive drug resistance in 59.38% (57/96; 95% CI: 48.87-69.29%) and pan drug resistance in 2.08% (2/96; 95% CI: 0.25-7.32%) of isolates, with a mean MAR index of 0.63 ± 0.17, highest among liver isolates (0.68 ± 0.16). Phenotypic ESBL positivity by the combined disk test was observed in 18.75% (18/96) of isolates, most frequently from the liver (22%). As identification relied on phenotypic method without molecular or virulence confirmation, these findings indicate that poultry may serve as a reservoir of phenotypically antimicrobial-resistant E. coli, with the liver showing the highest contamination and resistance burden, underscoring the need for targeted surveillance along Nepal's poultry supply chain.