Phenotypic and genotypic characterization of salmonella Isolated from Nile tilapia (Oreochromis ni/otics, L.) Along lake Victoria beaches in western Kenya

Abstract

Enteritis induced by nontyphoidal Salmonella represents major economic and social problems. Chemotherapeutic selection may have additional consequences for virulence evolution through acquisition of linked virulence genes. . Various foods have <..- been implicated as sources of Salmonellosis to humans. These include poultry, eggs, pork, and fish. Although prevalence of Salmonellosis is high in Western Kenya around Lake Victoria region, no particular food source has been identified to be associated with its transmission. Fish is the main source of protein for people living around the lake. Poor sanitary facilities at fishing beaches are likely to contaminate the lake waters. In Kenya, established quality control measures exist for export oriented but not locally consumed fish. The main objective of this study was to identify Samonella species and to perform their phenotypic and genotypic characterization in Winam gulf of L. Victoria .. A total of 120 fish specimens were collected of which 63 were positive for various bacteria isolates as determined by standard culture techniques and serotyping. Twenty-five (39.7%) were Shigella sp., 9 (14.3%) Salmonella enterica serotype typhimurium, 4 (6.3%) S. enterica serotype enteritidis, 7 (11.1 %) S. typhi, 16 (25.4%) Escherichia coli, 1 (1.6%) Proteus sp., and E. aerogenes respectively. Molecular typing of Salmonella involved the amplification of the house keeping gene for malic acid dehydogenase (mdh) with specific primers. Twenty Salmonella isolates had a gel ladder head resolved at 261 bp, which confirmed presence of malic acid dehydrogenase gene. Bands of 429 bp amplified regions using random sequence primers STll - STl5 further confirmed presence of Salmonella species in the isolates. Presence of Salmonella in Oreochromis niloticus was as a result of contamination of the fish during offloading but not during loading offshore.This study has provided vital data that is critical in assessing and controlling the risk associated with the presence of Salmonella in O. niloticus in the study area. For absolute safety, elimination of initial contamination of fish by enteric pathogens from the source should be ensured. Hence landing and marketing of fish from beaches with essential sanitary facilities can reduce the risk of cross contamination. Additional safety measures should include training in personal hygiene, sanitation and ensuring water quality.