Polymerase chain reaction fails to detect Listeria species from wild and cultured Nile Tilapia (Oreochromis niloticus) caught from a large freshwater lake in Zambia.

Fish have been identified as suitable vehicles for transmitting Listeria species to humans. Therefore, the thrust of this study was to determine possible Listeria species likely to circulate in freshly caught Nile tilapia (Oreochromis niloticus) in a large freshwater body. Accordingly, 150 Nile tilapia were sampled on landing. Of this number, half (n=75) were wild caught, while the other half (n=75) were from cage culture farms. All the sampled tilapia fish were independently caught from the same lake. Skin surfaces and gills were the only points sampled to restrict sites swabbed to those in contact with the environment. Swabs were processed using standard bacteriological culturing and identification tests. Only 2% (3/150) of the samples on culture and biochemical tests were presumptively Listeria. However, on Polymerase Chain Reaction (PCR), none yielded any noticeable results. None-detection of Listeria species on PCR may, in part, indicate the absence or undetectable levels in freshwater bodies. The detection of presumptive Listeria species phenotypically indicates possible contaminants other than Listeria. Our study has inherent limitations since it restricted itself to identifying contamination based on the fish's growth environment. We recommend determining the pathogen by incorporating enteric organs or whole fish analysis to increase isolation rates based on the current results. [ABSTRACT FROM AUTHOR]