Molecular characterization, antimicrobial resistance profiling, and biofilm analysis of Salmonella isolates from dead-in-shell embryonated eggs.

This study investigates the molecular characterization, antimicrobial resistance (AMR) profiling, and biofilm formation of Salmonella isolates from dead-in-shell embryonated eggs collected from 15 hatcheries in Bharatpur, Chitwan. A total of 210 samples were analyzed using cultural, biochemical, and molecular techniques, including PCR for virulence gene detection. The study revealed a prevalence rate of 11.42 %, with isolates demonstrating significant AMR, particularly to cephalexin (100 %), ampicillin (95.83 %), and nalidixic acid (91.67 %). Moreover, 83.33 % (n = 20) of the isolates were classified as multidrug-resistant (MDR), with a mean multiple antibiotic resistance index of 0.51. Biofilm formation analysis indicated that 70.83 % of the isolates could produce biofilms, with 41.67 % classified as weak producers and 16.67 % as strong producers. Molecular analysis identified key virulence genes, including invA (100 %), spvC (50 %), spvB1 (33.33 %), and the biofilm-associated gene agfA (12.5 %), emphasizing their roles in pathogenicity, systemic infections, and biofilm formation. Our findings highlight the critical public health risks posed by MDR Salmonella, which can persist in the food chain and compromise human and animal health. This research underscores the need for enhanced biosecurity in hatcheries, judicious use of antimicrobials, and periodic monitoring of bacterial resistance and virulence factors to mitigate the economic and health impacts of Salmonella infections in poultry production systems.