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 region, known as the nation’s “salad bowl,” produces more than 400 crops and has been linked to several foodborne illness outbreaks. The study aims to help scientists understand where disease-causing bacteria originate and how they spread, which is important for improving food safety in an area that supplies much of the country’s leafy greens.
Researchers from UC Davis worked closely with the FDA, the California Department of Food and Agriculture, 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.”
The team collected samples from soil, water sources, sediment, air, livestock feces, and wildlife across various ranches and vineyards. Atwill said: “We could not have done this without our partnership with the California livestock and produce industries.” Initial findings showed harmful strains of E. coli were detected in animal feces—including cattle, feral pigs, bobcats, deer, birds, coyotes—and sometimes persisted in older samples. The bacteria appeared less often in farm soil but were more frequently found near rivers or streams close to cattle ranches. Researchers also found these organisms in rivers and creeks but less often in irrigation runoff.
Multiple strains of E. coli O157:H7 were identified; however, none matched those linked to outbreaks between 2016 and 2020. Some strains found in wildlife closely matched those from cattle or environmental sources like water or soil. At one ranch different E. coli O157:H7 strains appeared each year among both cattle and wildlife but did not persist long-term.
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.” She 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 of hundreds of thousands of data points is ongoing with further updates expected later this year. The Western Center for Food Safety was established in 2008 as a Center of Excellence under the Human Foods Program with FDA.
