ANTIBIOTIC RESISTANCE PATTERN OF E. COLI AND SALMONELLA ISOLATED FROM DIARRHEIC CALVES IN PAKISTAN

Abstract

The problem of antimicrobial resistance in enteric bacteria from food-producing animals is becoming an increasing veterinary and public health issue. The present study assessed the isolation rates, antibiotic resistance profiles, and multidrug resistance of E. coli and Salmonella isolated from diarrheic calves in Pakistan using a hypothetical dataset developed for methodological training. A multi-center analytical cross-sectional design was used on 300 diarrheic calves aged between 2–90 days. Fecal samples were analyzed for E. coli and Salmonella, and the Salmonella isolates obtained were tested for susceptibility to 12 antibiotics using a disk diffusion-type susceptibility scheme. Descriptive statistics, chi-square tests, Fisher’s exact tests, Mann–Whitney U tests and multivariable binary logistic regression were carried out in IBM SPSS Statistics version 27. E. coli was isolated from 176 calves (58.7%), Salmonella from 89 calves (29.7%), and mixed E. coli and Salmonella isolation in 48 calves (16.0%). 84.1% of E. coli isolates and 69.7% of Salmonella isolates were multidrug-resistant. E. coli had the highest resistance to ampicillin, tetracycline, and streptomycin, while Salmonella had the highest resistance to tetracycline, ampicillin, and streptomycin. E. coli had significantly higher resistance to trimethoprim–sulfamethoxazole and ceftriaxone after applying Bonferroni adjustment. Multidrug resistance was independently associated with recent antibiotic use, and Salmonella isolates were less likely to be multidrug-resistant than E. coli isolates. These results emphasize the need to implement a culture-directed approach to treatment, antimicrobial stewardship, and veterinary oversight with routine resistance monitoring in calf production systems.