Prevalence, molecular characterization and antibiotic-resistance pattern of Salmonella spp. in aquaculture supply chain in Bangladesh

Abstract

Salmonella represents a persistent global health threat, primarily causing food-borne infections through contaminated animal-derived products, including poultry, eggs, and fish. In developing countries like Bangladesh, Salmonella is increasingly found as a diarrhea-causing agent. Despite its significance, systematic detection and monitoring of Salmonella within Bangladesh's aquaculture supply chain remains poorly understood, necessitating a comprehensive investigation into its prevalence and characteristics. The study examined 794 samples, a total of 400 fish samples (Pangas and Tilapia species) fish tank water (n=206) and cutting board swabs(n=188) were collected from various points along the supply chain including ponds(n=120), wholesale markets(n=100), and retail markets(n=574). Standard microbiological culture methods and molecular identification techniques were employed, with PCR analysis targeting the invasion (invA) marker gene. The investigation included detection of clinically relevant virulence genes (avrA, ssaQ, sodC1, bcfC) and antimicrobial susceptibility testing against 20 antibiotics using the Kirby-Bauer Disc Diffusion method. Analysis revealed that 32% (258/794) of fish samples tested positive for Salmonella species, with the highest incidence observed in retail markets 37%( n=211/574) followed by wholesale markets 23%(n=23/100) and ponds 20%(n=24/120).For environmental samples, Salmonella spp. Was detected in 35% of fish tank water samples and 38% of cutting board swab samples. Nalidixic acid and Tetracycline showed 10-11% resistance in both fish samples where as other antibiotics (Gentamycin, Pipeperacillin/Tazobactum, Meropenem, Ertapenem showed resistance within (0-3)% as well as Cefepime showed 0% resistaNce. Virulence gene analysis identified bcfC as the most prevalent gene (77%), followed by ssaQ (74%), avrA (69%) and sodC1(46%). The findings highlight the significant burden of Salmonella species within Bangladesh's Tilapia and Pangas aquaculture value chain. The study emphasizes the critical need for implementing a comprehensive One Health approach that integrates public health, aquaculture sector practices, and environmental health considerations. These results underscore the importance of developing and implementing effective risk reduction strategies in Bangladesh's aquaculture sector to ensure public health safety and sustainable aquaculture practices.