Abstract

A cross sectional study was conducted from November to June 2014/2015 in fish harvested for human consumption at Lake Zeway with the objective of isolating Edwardsiella tarda and Escherichia coli important pathogens and contaminants its products. Three hundred tissue samples comprising Spleen, Liver and Intestine were collected from 100 fish (12 Clarias gariepenus and 88 Oreochromis niloticus) originated from lake Zeway. Escherchia coli were isolated from spleen, liver, and the intestine of 12 out of 100 (12%) while E. tarda was isolated 4 out of 100 (4%) randomly examined fish. The higher percentage of both bacteria was isolated from intestinal samples than those isolated from liver and spleen samples. The E.tarda isolates appeared as small scatter pinkish colonies with black center while isolated colonies from E. coli were yellowish white on Xylose deoxycholate agar (XLD) after 24 h of incubation at 37°C Both types of isolates were gram negative short to medium rods, motile, catalase positive and oxidase negative. In biochemical test, both of the two types of typical isolates were positive for indole and Methyl red test and negative for Vagos proskaur test and unable to utilize Simmon’s citrate test. In addition to this, E. tarda ferments sodium thiosulfate and result its byproduct of H₂S production (blackening) on TSI test which were absent in E.coli. The distribution of E.tarda and E.coli infection among the three organs examined indicate both bacteria were isolated most frequently from intestine followed by spleen and liver with significance difference (P <0.05) in the rate of isolation among organs. The occurrence of E.tarda and E.coli infection with respect to sex were not significant (P>0.05) indicating that sex has no role in influencing the exposure these bacteria. The isolation of E.tarda and Escherchia coli from wild fish population of Lake Zeway destined for human consumption in the current study indicated that E. tarda and Escherchia coli are a potential threat for fish and public health.

Key word: Catfish, Escherchia coli, Edwardsiella tarda, intestine, liver, spleen tilapia, zeway.