Prevalence, characteristics and antibiogram profile of Escherichia coli O157:H7 isolated from raw and fermented (nono) milk in Benin City, Nigeria

Abstract

Background: Most Escherichia coli strains are harmless commensals, but some serotypes can cause serious food poisoning in their hosts, and are infrequently responsible for product recalls due to food contamination. The present study was carried out to determine the occurrence of E. coli O157:H7 and other E. coli strains from raw and fermented (nono) milk in Benin City, Nigeria.
Methodology: A total of 66 (33 raw and 33 nono) milk samples were obtained from retailers from 3 different stations in Aduwawa market, Benin City, Nigeria between January and June, 2017. Samples were analysed by cultural methods for faecal coliforms using M-Fc agar, E. coli using Chromocult coliform agar, and E. coli O157:H7 using sorbitol MacConkey agar supplemented with cefixime and potassium tellurite. Presumptive E. coli andE. coli O157:H7 isolates were confirmed by polymerase chain reaction (PCR) assay using specific primers. Antimicrobial susceptibility profile of confirmed isolates was performed using the Kirby-Bauer disk diffusion method, with zones of inhibition interpreted according to the guidelines of Clinical and Laboratory Standards Institute (CLSI). Data were  analysed using the SPSS version 21.0.
Results: From the 66 nono and raw milk samples assessed in this study, all (100%) were phenotypically positive for E. coli O157:H7. A total of 19 E. coli O157:H7 and 41 other strains of E. coli were confirmed by PCR. The resistance profile of the 19 E. coli O157:H7 isolates showed 100% (19/19) resistance to penicillin G and ampicillin; 94.7% (18/19) to chloramphenicol; 89.5% (17/19) to erythromycin; and 78.9% (15/19) to sulfamethoxazole and oxytetracycline, while the sensitivity profile showed that 100% (19/19) E. coli O157:H7 isolates were sensitive to gentamicin and ofloxacin. The resistance profile of other 41 E. coli isolates showed 100% (41/41) resistance to penicillin G and ampicillin; 97.6% (40/41) to chloramphenicol; and 92.7% (38/41) to erythromycin, while 97.6% (40/41) were sensitive to  gentamicin and kanamycin. Ten E. coli O157:H7 isolates (52.6%) showed extensive drug resistance pattern to 11 antibiotics in 7  antimicrobial classes with multiple antibiotic resistance (MAR) index of 0.46.
Conclusion: Findings from the present study clearly indicated that the safety and quality of fresh and fermented milk were not satisfactory and could be of public health concern.

Key words: Nono, Escherichia coli; Pathotypes, Resistance index, Public health, Milk