Isolation of Salmonella and Shigella from fish harvested from the Winam Gulf of Lake Victoria, Kenya

Abstract

Background: Human infections caused by pathogens transmitted from fish are quite common. The aim of this study was to isolate enteric pathogenic bacteria from fish that might be transmitted to humans after the handling or consumption of such fish. Methodology: One hundred and twenty Nile tilapia fish harvested using various fishing methods were collected from fishermen in five fish landing beaches within Winam Gulf and disinfected externally using 70% ethyl alcohol for 2 minutes then washed three times with autoclaved distilled water. Isolation of Salmonella and Shigella species from fish samples was performed using standard bacteriological procedures. Five milliliters of each fish tissue slurry was microbiologically analyzed for any Enterobacteriaceae. Twelve Nile tilapia collected from three open-air markets were analyzed for Enterobacteriaceae comparison as controls. Identification of Salmonella by using housekeeping genes and species-specific primers was performed. Results: Among 120 Nile tilapia, 63 (52.5%) were infected with Enterobacteriaceae. Out of these, 25 (39.7%) were Shigella spp, 9 (14.3%) Salmonella typhimurium, 7 (11.1%) S. typhi, 4 (6.3%) S. enteritidis, 16 (25.4%) Escherichia coli, 1 (1.6%) Proteus spp. and Enterobacter aerogenes respectively. Ten fish collected from open-air markets yielded E. coli (50%), S. typhimurium (20%), S. paratyphi (10%) and S. typhi (20%). Conclusion: Nile tilapia within Winam Gulf are infected by human enteric pathogens. Shigella spp., Salmonella and E. coli were the most frequently isolated, an indication that the beaches may be contaminated by untreated municipal sewage, runoff, and storm-water. S. typhimurium, S. typhi and S. enteritidis were the most common Salmonella isolates.