Prevalence and antimicrobial susceptibility of pathogenic Escherichia coli O157 in fresh produce obtained from irrigated fields

• Potential public health risks associated with irrigated vegetables in Nigeria.
• E. coli O157 showed marked phenotypic resistance to commonly used antibiotics.
• Genotypic characterization showed strains had antibiotic resistance genes.

Escherichia coli O157 has been implicated in many outbreaks of gastroenteritis associated with the consumption of contaminated fresh vegetables, fruits and sprouts. In Nigeria, the use of untreated wastewater in irrigation is largely considered an inevitable option to compensate for water shortages. This study investigated the seasonal prevalence and antimicrobial susceptibility of potentially pathogenic E. coli O157 from fresh produce in two large vegetable producing areas in Nigeria (Kano and Plateau States). Four hundred and forty samples, comprising fresh produce (238), irrigation water (84), and soil/manure samples (118) were collected from May, 2010 to March 2011, and analyzed for the presence of potentially pathogenic E. coli O157. Overall, 7.3% (32/440) samples were identified as E. coli O157 with its highest detection from Kano State 18/230 (12.2%). E. coli O157 was 3 times higher in vegetables during wet season than dry season and 2.3 times higher in irrigation water in wet season than in dry season. E. coli   O157 was tested for their susceptibility to eight commonly used antibiotics and by Polymerase Chain Reaction (PCR) for the presence of; uidAA, O157 and genes coding for the quinolone resistance-determining region (gyrAA) and plasmid (pCT) coding for multidrug resistance. The confirmed isolates showed that 30/32 (93.8%) were resistant to two or more antibiotics distributed in seven different multidrug resistance patterns. Our results reflect occurrence of multidrug resistant E. coli O157 in these major produce regions. We recommend adequate treatment of wastewater before use to avoid possible public health hazards from consumption of these vegetables.