Shiga Toxin (Stx) Gene Detection and Verotoxigenic Potentials of Non- 0157 Escherichia Coli Isolated from Fermented Fresh Cow Milk (Nono) Sold in Selected Cities in Nigeria

Abstract

Non-0157 Escherichia coli, isolated from Nono (fermented fresh cow milk) sampled from four major Nigerian cities, namely, Abuja, Benin City, Lagos and Onitsha were investigated for the presence shiga toxins (stx1 and stx2) genes using PCR technique and for their verotoxigenic potentials using tissue culture assay on Vero cells. The result of the investigation reveal that out of the total 800 samples collected, 268 (33%) had E. coli and out of this, 217 (81%) had non-0157 E. coli. Total number of non-0157 E. coli isolated from the 217 samples was 503. Shiga toxin gene detection of the isolates revealed that 199(40%) had stx1 gene alone, 192 (38%) had stx2 gene alone, 4(1%) had both stx 1 and stx 2 genes while 108 (21%) had none of the two genes. Tissue culture assay on Vero cells indicate that there is a strong relationship between the presence of stx genes and their degree of cytotoxic effect on vero cells as over 80% of the isolates without the genes exhibited weak cytotoxic effect whereas over 80% of those with the stx genes exhibited varying degrees of cytotoxic effects ranging from strong to excellently strong. This study provides evidence of presence of non-0157 E. coli in our food system and can be of serious health challenge to consumers.

Keywords: Non- 0157 Escherichia coli, Shiga toxins, Verotoxigenic, Nono, Fermented Milk