Prevalence of Antimicrobial Resistant Salmonella Spp. in Chicken Egg Supply Chain

Abstract

Aim: The present study aimed to determine the prevalence of antibiotic-resistance pattern of Salmonella spp. in the chicken egg supply chain of Maharashtra, India. Study Design: cross-sectional prospective study Place and Duration of Study: The study was conducted across various districts of Maharashtra, India, from September 2024 to March 2025. Methodology: A total of 390 various samples (cloacal swabs, faeces, feed, water, and eggs) from commercial layer, backyard poultry farms, egg distributors and retail eggs were collected and processed using standard protocols. Isolation of Salmonella spp. was carried out through cultural methods followed by molecular confirmation with 16S rRNA PCR. Isolates were characterized by Congo red binding and invA gene PCR assay. Considering pathogenicity all invA gene PCR isolates were subjected to antibiotic susceptibility testing and screened for antimicrobial resistance genes targeting tetracycline, sulphonamide and ESBL group of antimicrobials. Results: Out of 390 samples, 21 (5.38%) were confirmed as Salmonella spp. by 16S rRNA gene PCR assay. All showed Congo red binding, while 14 (66.7%) were invA positive, indicating a prevalence rate of 3.59% for invasive Salmonella spp. The prevalence was found highest among egg distributors (8.34%), followed by retail eggs (6.67%), commercial farms (3.34%) and backyard poultry (1.12%). The invA positive Salmonella spp. were found to be more prevalent in commercial layer farms compared to backyard poultry farms. Amongst invA positive isolates, 2 (14.28%) were identified as Salmonella Typhimurium and the rest were non typable. Antibiotic susceptibility testing revealed resistance to Ampicillin (100%) and Ceftazidime (93%). Further isolates were found to be sensitive to Chloramphenicol (100%) and Gentamicin (93%). The average MAR index was 0.270, with 85.7% of isolates were multidrug resistant. Genotypic analysis of isolates revealed the presence of tetA (7.14%) and Sul1 (14.2%) genes, without expression of beta-lactamase genes. Conclusion: The findings highlight the presence of antimicrobial resistant Salmonella spp., in egg supply chain, but continuous surveillance and monitoring of Salmonella spp. remain crucial. The applications of strict control measure on antibiotic use to prevent the spread of multidrug-resistant Salmonella strains, is essential for protecting and safeguarding public health.