Minimum inhibitory concentration of antibiotics to salmonella of poultry origin in selected regions of Nepal

Abstract

Antimicrobial resistance (AMR) in Salmonella from poultry is an emerging threat to animal and public health, yet quantitative minimum inhibitory concentration (MIC) data from Nepal remain scarce. This study aimed to determine the MIC profiles of Salmonella isolates from layer poultry farms and identify farm-level factors associated with multidrug resistance (MDR). A cross-sectional survey was conducted between March 2020 and March 2023, during which 1,080 cloacal swab and litter samples were collected from 180 layer farms across Kaski, Chitwan, Makawanpur, and Dang districts. Salmonella was detected in 65 samples (6.01%) by culture and PCR targeting the invA gene, and MICs for 15 antimicrobials were determined using E-test strips and interpreted according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) epidemiological cut-off values. High resistance was observed to tetracycline (87.69%), doxycycline (81.54%), ciprofloxacin (78.46%), norfloxacin (69.23%), amoxicillin (53.85%), and chloramphenicol (50.77%), whereas amikacin exhibited the lowest resistance (10.77%). Correlation analysis revealed co-resistance among β-lactam and tetracycline antibiotics, indicating antimicrobial selection pressure within poultry production systems. Poisson regression identified the objective of antibiotic use (IRR = 0.289, p = 0.029), dose measurement practices (IRR = 0.619, p = 0.021), and outcomes of the last antibiotic treatment episode (IRR = 0.284, p = 0.011) as significant predictors of MDR. This study provides the first comprehensive MIC-based evidence of Salmonella AMR in Nepalese layer poultry, emphasizing the need for routine MIC-based surveillance, strengthened antimicrobial stewardship, and evidence-based antibiotic use policies to curb MDR and protect food safety within a One Health framework.