Five-year study reveals how harmful bacteria move across farms and wildlife
A major five-year environmental study led by federal scientists and university researchers is helping improve the understanding of how harmful bacteria move through farm environments. The research focused on California’s Central Coast, a region often called the nation’s “salad bowl” because it produces hundreds of crops, including a large share of leafy greens grown in the United States.
The project was launched after several foodborne illness outbreaks linked to the region. In 2020, federal food safety officials asked researchers from the Western Center for Food Safety at the University of California, Davis, to help lead a large environmental study to identify where disease causes bacteria to come from and how they spread.
The research team worked closely with many partners including government agencies, ranchers, growers, and landowners. Scientists collected samples from different environmental sources such as soil, surface water, sediment and air near produce fields. They also gathered fecal samples from livestock and wildlife living around ranches and vineyards.
“This was a five-year collaborative effort to test the environment within and surrounding produce fields, such as soil, surface water, sediment and air,” said Rob Atwill, a principal investigator for the Western Center for Food Safety and epidemiologist with the UC Davis Weill School of Veterinary Medicine. “We could not have done this without our partnership with the California livestock and produce industries.”
Early findings show that harmful strains of E. coli were detected in several environmental sources and animal species. These included cattle, feral pigs, deer, bobcats, coyotes, birds, and even flies. Researchers also found the bacteria in rivers, creeks, and sediments. However, the bacteria appeared less frequently in farm soil, except near waterways and cattle ranches.
Researchers identified multiple strains of E. coli O157:H7 in environmental samples, but none matched the strains connected to major outbreaks that occurred between 2016 and 2020. Some illnesses causing strains were found to remain in the environment for nearly two years.
“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,” said Linda J. Harris, co-principal investigator with the Western Center for Food Safety and professor emerita in the UC Davis Food Science and Technology department.
“These data will be used by the industry to inform future targeted research and refinements, if needed, to provide existing guidance on best practices for growers to reduce food safety risks,” said Harris.
Scientists say the results confirm that these bacteria naturally exist in the environment. The findings will help growers improve food safety practices and guide future research efforts to reduce contamination risks in producing farming systems.
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