Is Local Produce Safer? Microbiological Quality of Fresh Lettuce and Spinach from Grocery Stores and Farmers' Markets

There is a growing demand for fresh, safe, high-quality, and locally grown vegetables. This study compared microbial populations in Romaine lettuce, Bibb lettuce, and spinach procured from grocery stores and farmers’ markets throughout the course of a summer. Standard microbial techniques were used to analyze 42 samples for the presence of total aerobic mesophilic and psychrophilic bacteria; yeasts and molds; surface and internalized coliforms and Escherichia coli; and the pathogens E. coli O157:H7 and Salmonella spp. Large variations in counts were found between produce types, sampling days, and between grocery and farmers’ market samples. The average highest microbial loads were associated with spinach samples from the grocery store, with both total aerobic mesophilic and psychrophilic counts greater than 7.1 log CFU/g. Average psychrophilic counts were higher than mesophilic microorganisms in all samples tested. In general, lettuce from farmers’ markets had more bacterial, yeast, and mold presence than lettuce from grocery stores.