Although fish in the retail markets in Bangladesh is generally conceived to be fresh, they might carry human pathogenic bacteria. Microbial contamination of fish can occur at different stages of the supply chain and therefore a thorough assessment of the dynamics of changes in the level of contamination is important for understanding ways to control such risks in Bangladesh. Data from samples can serve as input into a microbial risk assessment that will aid in future evaluations of potential mitigation strategies focused on reducing human pathogenic bacteria in aquaculture. This study assesses contamination of tilapia and pangas with fecal pathogens and practices of stakeholders along the supply chain that might be associated with the contamination.
A total of 368 whole fish samples (tilapia, n=188 and pangas, n=180) were collected from 17 retail markets (n=188), 5 wholesale markets (n=100), and 8 grower ponds (n=80). Fish samples were tested for E. coli, extended-spectrum β-lactamase producing E. coli (ESBL-Ec), Salmonella spp. and Vibrio cholerae following standard methods. Surveys were used to collect and analyze data on handling practices of 410 selected actors in the fish supply chain comprising 144 retailers, 144 cut-up table workers, 72 wholesalers, and 50 producers.
The prevalence of E. coli (p<0.001), and V. cholerae (p<0.001) but not ESBL-Ec (p= 0.747) and Salmonella spp. was significantly higher in both tilapia and pangas in the retail markets compared to wholesale markets and grower’s ponds. ESBL-Ec and Salmonella spp. were more prevalent only in tilapia from ponds (Fig. 1). The median count of E. coli in both fishes increased significantly from grower’s ponds (1.4 log10 CFU/g of fish, IQR= 2.0) to wholesale (2.3 log10 CFU/g, IQR= 1.3) and retail sale (2.8 log10 CFU/g, IQR= 1.0) (p=0.015) whereas ESBL-Ec was consistent (Fig. 2).
Majority of fish producers (92%) used antibiotics in ponds without prescription. Around 97% of the wholesalers transported fish in trucks lacking a cold chain. Fish were often processed at unhygienic landing sites using a single knife with improper washing due to the lack of running water. The high prevalence of fecal bacteria and unhygienic practices by supply chain actors implied a poor knowledge and infrastructure for post-harvest management in aquaculture.