ABSTRACT
A total of 800 “Nunu” (a fermented fresh milk product) made up of 200 samples each from four major Nigerian cities, namely Abuja, Benin City, Lagos and Onitsha were investigated for the presence and prevalence rate of Enterohaemorrhagic Escherichia coli 0157:H7, using standard microbiological procedures on Sorbitol-MacConkey agar supplanted with cefixime and potassium tellurite (CT-SMCA). All non sorbitol fermenting isolates which were colourless on CT-SMCA, suspected to be Escherichia coli 0157:H7 were characterised serologically using Oxoid Latex agglutination kit and molecularly with PCR techniques. Tissue culture assay to determine the verotoxigenic potentials of all confirmed Escherichia coli 0157:H7 was done on Vero cells. Overall, E. coli was isolated from 268 (33.50%) samples, out of which 51(6.38%) were non sorbitol fermenting E. coli. Non sorbitol fermenters were isolated the most from samples collected in Lagos 17(8.50%) while Benin City recorded the lowest with 7(3.50%). Number of non sorbitol fermenting E. coli isolated from the survey was 31, 16, 58, and 43 from Abuja,
Benin City, Lagos and Onitsha respectively. Of these, 9, 6, 17 and 21 were respectively confirmed as E. coli 0157:H7 with serological characterisation while molecular characterisation with PCR gave a varied result of 7, 5, 13, and 16 respectively. Tissue culture assay on Vero cells confirmed all the E. coli 0157:H7 isolates to be highly verotoxigenic. The findings from this study provide evidence of the presence of E. coli 0157:H7 in our food system as such, health authorities are advised on the need to properly monitor the production and sales of “Nunu” to prevent potential outbreak.
KEYWORDS: Escherichia coli 0157:H7, Verotoxigenic, Nunu, Fermented Milk