A cross-sectional study was conducted to estimate the prevalence, serotypes, antimicrobial resistance and plasmids profiles of Salmonella spp. in Nile perch of Lake Victoria, Tanzania. Salmonella spp. and Escherichia coli in water and fish samples were investigated using bacteriological methods. Antimicrobial resistance profiles of Salmonella spp. were determined using the minimum inhibitory concentration (MIC) method. A total of 352 samples were analysed including Nile perch, water and swabs from surfaces of facilities used for fish transport. The finding showed Salmonella spp. prevalence in fish at fishing ground were 16/60 (26.7%), landing sites and markets were 9/60 (15%) and 18/60 (30%) respectively. A significant difference (p<0.05) was observed between Salmonella spp. prevalence in fish from fishing ground and those at landing sites, but not with those from markets (p>0.05). The main serotypes recovered were Salmonella ser. Waycross (41:z4z23 :-) and Salmonella enterica ssp. salamae (42:r :-). Most Salmonella serotypes showed low resistance profiles against most of antimicrobials, but few isolates were resistant to Nalidixic acid 3/64 (4.7%), ampicillin 5/64 (7.8%), azithromycin 14/64 (21.9%) and sulfamethoxazole 22/64 (34.4%). Plasmids were detected in few S. ser. Waycross compared to none of S. ssp. salamae. Escherichia coli count ranged 0.77 to 2.44 log10 cfu/g in fish and 0.44 to 1.71 log10 cfu/ml in water. Contaminated fish with different Salmonella serovars imply pollution of the lake attributable to waste from point and nonpoint sources that may contain antibiotic residues accounting for resistant bacteria in aquatic environment.

Keywords: Fishing ground; landing sites; local markets; antimicrobial resistance; plasmids