A five-year study led by the U.S. Food and Drug Administration and the Western Center for Food Safety at the University of California, Davis, is providing new insights into how harmful bacteria move through the environment on California’s Central Coast, according to a March 12 announcement.
The Central Coast is known as the nation’s “salad bowl,” producing more than 400 crops, including much of the country’s leafy greens. The region has been linked to several foodborne illness outbreaks in recent years. In response, the FDA asked UC Davis researchers in 2020 to help conduct a large-scale environmental study to better understand sources and movement of disease-causing bacteria.
The research involved collaboration between federal agencies, state officials, ranchers, landowners, and growers. Rob Atwill, principal investigator for the Western Center for Food Safety and epidemiologist with the UC Davis Weill School of Veterinary Medicine, said: “This was a five-year collaborative effort to test the environment within and surrounding produce fields, such as soil, surface water, sediment and air.”
Researchers collected samples from soil, water sources, sediment, air, livestock feces and wildlife across ranches and vineyards. Atwill said: “We could not have done this without our partnership with the California livestock and produce industries.”
Initial findings show that harmful strains of E. coli—including those that can cause serious human illness—were detected in animal feces from cattle, feral pigs, bobcats, deer, birds, coyotes and flies. The bacteria were also found in older samples under various conditions. While farm soil overall showed less frequent presence of these bacteria compared to other sources, higher levels were found near rivers or streams close to cattle ranches. Surface water appeared to play a role in helping bacteria survive and move through landscapes.
Researchers identified multiple strains of E. coli O157:H7 but did not find any directly linked to previous outbreaks between 2016 and 2020. Some strains found in wildlife closely matched those found in cattle or environmental samples like water or soil; several persisted for nearly two years.
Linda J. Harris, co-principal investigator with the Western Center for Food Safety and professor emerita at UC Davis Food Science and Technology department said: “The agricultural industry has made a lot of changes in the last decade to address food safety issues and our data support that they are focused on the right things.” Harris added: “These data will be used by the industry to inform future targeted research and refinements, if needed, to existing guidance on best practices for growers to reduce food safety risks.”
Analysis continues on hundreds of thousands of data points collected during this study with further updates expected later this year. The Western Center for Food Safety was established in 2008 as a Center of Excellence under FDA’s Human Foods Program.
