Shiga toxin-producing Escherichia coli O157:H7 in milk and milk products in Ogun State, Nigeria

Shiga toxin producing Escherichia coli (STEC) O157 is a major cause of food-borne illnesses in humans. This study investigated the presence of STEC O157 in milk and milk products in Ogun State, Nigeria. Of a total of 202 samples 10 (5%) were positive for STEC O157 including 1 (2%) of 50 raw milk samples, 3 (6%) of 50 samples of fresh local cheese, 1 (2%) of 50 samples of fried local cheese and 5 (9.6%) of 52 fermented milk samples. There was no significant difference (p>0.05) in the prevalence of STEC O157 among the sample types. Of 10 isolates, shiga toxin 1 gene (stx1) was detected only in 2 samples (20%), shiga toxin 2 (stx2) was extracted only in 6 samples (60%), stx1 /stx2 in 2 samples (20.0%), intimin gene (eaeA) in 5 samples (50%), and enterohaemolysin (E-hlyA) gene was isolated in 7 (70%) samples. Rates of resistance of the STEC O157 isolates were: amoxicillin/clavulanic acid 100%, ampicillin 100%, chloramphenicol 60%, nalidixic acid 20%, norfloxacin 10%, streptomycin 30%, sulphamethoxazole/trimethprim 20%, and tetracycline 90%. The isolates were all susceptible to ciprofloxacin and neomycin. The presence of virulent multidrug resistant E. coli O157 strains in milk and milk products as revealed by this study unveils a risk of human exposure to these potentially fatal pathogens following consumption of contaminated products.