Purpose: This study examines the effect of seasonal variations on the microbial safety of lettuce in Lagos State.
Methods: Samples of field source lettuce (n = 90), irrigation water (n = 30) and manure (n = 30) used on farm were collected monthly for five months (August to December 2013) for microbial analysis using standard bacteriological techniques; Total Plate Count (TPC), Total Coliform Count (TCC), Escherichia coli, Listeria spp., Salmonella spp., and Shigella spp. counts. Farmers whose farms were sampled were assessed on adoption of Good Agricultural Practices (GAP) pertaining to food safety through questionnaires. Relative humidity (RH), temperature and rainfall data were obtained from Nigeria Meteorological Station. Risk hazard map was constructed.
Results: TPC, TCC, Listeria ranges were: 5.87 - 8.14, 4.62 - 6.71, 4.15 - 6.19 log CFU/g while Shigella, E. coli and Salmonella spp. counts were 3.16 - 4.09, 3.16 - 4.09 and 3.00 - 3.26 log CFU/25g of lettuce samples, respectively. Counts of isolated pathogens exceeded the international safety limits. Salmonella, Shigella, E. coli counts and TPC had a negative correlation with RH and a positive correlation with rainfall. Irrigation water and rainfall had a positive correlation with the microbial count except Salmonella spp. count. Manure had a positive correlation with all the microbial counts. Of the respondents 26.7% were GAP adopters; 40% moderately adopted GAP and 33.3% were non-GAP adopters – highest microbial load was obtained from these category.
Significance: This study suggested that seasonal variation influences lettuce contamination, although sources other than irrigation water and manure initiated contamination. The institution of GAP on farm to improve microbial safety of lettuce produced for public consumption is emphasized.