Microbiological survey of locally grown lettuce sold at farmers' markets in Vancouver, British Columbia.

Increased consumer demand for fresh leafy produce has been paralleled by an increase in outbreaks and illness associated with these foods. Presently, data on the microbiological quality and safety of produce harvested in the Lower Mainland of British Columbia is lacking. Therefore, fresh green, red, and romaine lettuce samples (n = 68) were obtained from five regional farmers' markets in late summer of 2012 and subsequently analyzed to determine total numbers of aerobic bacteria, coliforms, and Escherichia coli. Additionally, enrichment procedures were used to detect low concentrations of E. coli. Obtained E. coli isolates were subjected to multiplex PCRs to determine phylogenetic groupings and the presence of virulence genes (eaeA, hlyA, stx1, and stx2). All E. coli were tested for resistance to 15 antibiotics using a disk diffusion assay. Lettuce samples yielded mean aerobic colony counts of 6.3 log CFU/g. Coliforms were detected in 72% of samples, with a median concentration of 1.9 log CFU/g. Of sample...