Genomic Characterization and Plasmid Profile of Listeria and Salmonella Species Isolated from Oreochromis niloticus Sold in Port Harcourt, Rivers State, Nigeria
Fish are generally regarded as safe, nutritious and beneficial but aquaculture products have sometimes been associated with certain food safety issues. Consumption of fish may also cause diseases due to infection or intoxication, Hence, the aim of this study is to characterize using genomic analysis and plasmid profile of Listeria and Salmonella species isolated from Oreochromis niloticus sold in Port Harcourt. A total of one hundred and eighty samples (180) were collected from three different markets namely; Creek road, Mile one and Rumuokoro markets over a period of six months. The samples were labelled and transported in an ice packed coolers to the laboratory for analyses. Standard analytical protocols were employed to determine the bacteriological characteristics of the various parts such as Intestine, Gill, flesh of the sample. Statistical analyses were carried out using ANOVA and All pairs tukey-kramer. Results obtained from the study showed that the total heterotrophic bacteria count ranged from 5.1 to 5.9 x10 x106cfu/g across the markets for the flesh part, 6.0 to 7.7 x106 cfu/g (Gill) and 7.1 to 7.6 x106 cfu/g for the intestinal samples. Total coliform count ranged from 4.2 to 5.4 x104cfu/g (flesh), 5.2 to 5.4 x104 cfu/g ((Gill) and 6.1 to 8.0 x104 cfu/g (Intestine). Listeria count range from 2.7 to 2.9 x104 cfu/g (Fresh), 3.3 to 3.7 cfu/g (Gill)), and 3.8 to 4.3 cfu/g (Intestine), and Salmonella count ranged from 1.0 x103 - 1 .1 x103 cfu/g (Flesh) 1.0 to 1.6 x103 cfu/g (Gill) and 1.2 to 2.0 x103 cfu/g (intestine). This results shows that the intestines harbours more bacterial load than the gill and flesh. Mean values for all the microbial counts were significantly different (P<0.05) in the three samples across the sampled markets The result of the conventional and genomics identification confirms the following species of Listeria and Salmonella: L. grayi VD-Sfg with accession number MW020239 having a closest gene bank match with Listeria grayi CIP 100% identified, L. monocytogenes VD-Sfg with accession number MW020240 closest to L. monocytogenes NCTC 10357 with 99.73% identified, L. seeligeri VD-SFF accession number MW020241 closet to L. seeligeri ATCC 35967 with 98.95%, L. welshimeri VD-SF MW020242 closest to L. welshimeri ATCC 35897 with 99.9%, L. monocytogenes VD-Fg MW020243 closet to L. monocytogenes NCTC 10357 eith 99.73% identity, S. bongori VD-SwfiA MW020245 closest to S. bongori NCTC 12419 and S. enterica VD-SwfiD MW20244 closest with S. entrica LT2 both with 100% identity. Gel electrophoresis of the plasmid DNA showed that all the isolates possess plasmid. This finding is of public health concern as these organisms are the known causes of food-borne diseases and also serve as reservoirs for resistance plasmids that may be transferred to otherwise susceptible bacteria making them resistant, thus increasing the occurrence of antibiotic resistance among microorganisms.