Occurrence of Enteric Pathogens on Fresh Produce Grown on Irrigated Soils

Aims: To assess the potential health risks of fresh produce grown on irrigated soils treated with manure in Kano State, a large produce region in Nigeria.
Methodology: Fresh produce irrigated with wastewater on manure treated soils were assessed for the prevalence, serotype distribution and toxigenicity of Escherichia coli O157, Salmonella spp and Vibrio cholerae in a large produce region in Nigeria. A total of 230 samples obtained from five designated produce locations were examined using selective isolation method with prior enrichment. Fresh produce comprised carrots, cabbage, cucumber, lettuce, tomatoes, spinach, green peas and spring onions. Suspect isolates were identified and characterized by conventional biochemical methods and Microbact 24E (Oxoid, UK) kit. Confirmed isolates were serotyped and E. coli O157 and Vibrio cholerae O1 were assayed for their toxigenic potentials using the Reverse Passive Latex Agglutination kit. The enterotoxigenicity of Salmonella spp was determined by detection of stn gene using polymerase chain reaction (PCR) techniques.
Results: Results obtained showed that overall, Salmonella spp and Escherichia coli O157 had the highest prevalence of 17.0% and 10.9%, respectively. Both were most commonly detected from fresh produce. The serotypes of Salmonella detected include Salmonella typhi (51.3%), Salmonella paratyhpi (20.5%) and Salmonella typhimurium (28.2%); strains of Vibrio cholerae O1 detected include Vibrio cholerae O1 of the Ogawa, Inaba and the Hikojima serotypes.
Conclusion: The use of untreated irrigation water in vegetable production represents a significant route of transmission of diarrheal pathogen to humans and hence represents a public health risk. We recommend proper and adequate wastewater treatment before use.