Isolation and Identification of Pathogenic Bacteria Present in Commercially Important Fish, Shellfish, Water, and Soil Samples of Kaptai Lake, Bangladesh

This study aimed to analyse the enteric pathogenic bacteria, in fish, soil, and water collected from Kaptai Lake that could be transmitted to humans through handling and consumption. Various types of selective agar media were used to isolate Escherichia coli, Salmonella, Shigella, Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus. After observing the culture morphology, microscopic examination, and biochemical tests were performed. Total plate count indicated varying levels of bacterial load among 20 fish species, Puntius ticto exhibiting the highest (8.53 ± 0.21 × 10⁶ CFU/g) microbial load. Among the soil and water samples, Guccha gram (in Baghaichari) exhibited the highest bacterial load (6.13 ± 0.66 × 10⁶ CFU/g and 3.90 ± 0.20 × 10⁶ CFU/mL, respectively). E. coli in most water and soil samples suggested potential contamination by human and animal faecal matter. Bacterial risk indices showed that 13 fish species among 20 fish samples were categorised as 'Good', indicating safe for consumption, and the remaining 7 fish species were identified as 'Acceptable'. The correlation matrix showed high correlation scores in most places (from 0.5 to 1), indicating that environmental hygiene matters most for the safety of fish. Higher microbial load in soil, water and fish samples emphasises the necessity for strict adherence to reduce zoonotic diseases.