A cross-sectional survey was conducted during summer 2013 to determine the occurrence of Escherichia coli, fecal coliforms (FCs), E. coli O157:H7, and Salmonella on raw vegetable commodities common to Asian cuisine from 21 vendors or farmers at six farmers' markets in northern California. Based on 242 samples from six commodities (basil, yardlong beans, bitter squash, okra, squash stems and leaves, cilantro), 100% of samples had detectable FCs and 20% had detectable E. coli. The mean concentrations were 0.67 log CFU/g and 1.26 log CFU per bundle for E. coli and 4.00 log CFU/g and 6.26 log CFU per bundle for FCs. Vegetables irrigated with ground versus surface water contained lower concentrations of FCs, but this difference was not observed for E. coli. Yardlong beans, bitter squash, and okra had lower levels of FCs compared with basil, cilantro, and squash stems and leaves. Sixteen (6.6%) samples had detectable levels of Salmonella serovars (Newport, Enteritidis, Agona, and Worthington), with the majority of positives found in cilantro and squash stems and leaves. There was a twofold higher probability of Salmonella contamination in samples from growers or vendors who stated that they used organic farming practices compared with samples from those using conventional farming practices. Lastly, the concentrations of FC and E. coli bacteria were significantly associated with Salmonella contamination: for each additional 100 CFU/g or bundle, the probability of Salmonella contamination increased by ∼15 and ∼30%, respectively. None of the samples had detectable E. coli O157:H7.

The presence of livestock in or near fresh-market vegetable fields has raised concerns about the potential for contaminating produce with pathogenic bacteria. To develop buffer zones for grazing near production of leafy greens, we assessed the prevalence of Escherichia coli O157:H7 and Salmonella species in sheep that were grazed on alfalfa fields during the winter in California's Imperial Valley. We found E. coli O157:H7 in 1.8% of fecal samples and 0.4% of soil samples, and Salmonella in 0.8% of fecal samples and 0.4% of soil samples. Our results indicate that sheep grazing on alfalfa in the Imperial Valley have a low prevalence of these pathogens in their feces and that these bacteria are rarely found in soil from fields with grazing sheep. The California Leafy Green Products Handler Marketing Agreement guideline of 30 feet between grazing lands or domestic animals and the crop edge is adequate to minimize potential contamination of nearby crops.