Surveillance of Zoonotic Bacterial Pathogens in Agricultural Environments

• Paige Andrade, Pre-Veterinary Medicine and Animal Biosciences, University of Delaware

• Dr. Kali Kniel, Animal and Food Sciences, University of Delaware

Zoonotic bacterial pathogens such as Escherichia coli, Salmonella enterica spp., and Listeria monocytogenes are among the leading causes of foodborne illnesses in the United States, posing serious risks to public health when contaminated produce is consumed. One means to reduce these risks is through surveillance of contamination prior to distribution. To reduce the risk of potential recalls, the Produce Safety Research Consortium, a regional surveillance initiative, aims to inform produce safety issues through detection of these pathogens early by working with small to mid-sized farms across the northeastern U.S. to improve on-farm food safety practices. Environmental samples were collected weekly from multiple farms across the region, including soil samples from growing areas and swabs from post-harvest production lines. Swabs and soil samples were tested for indicator organisms using Charm plates for coliforms and E. coli, and RAPID’L.mono agar for L. monocytogenes. Samples were serially diluted and bacteria enumerated on selective media following incubation for 24 hours. Similarly, XLT4 agar was used to detect Salmonella, with duplicate plates of serial dilutions incubated for 48 hours. If any colonies were observed indicative of presumptive Salmonella or L. monocytogenes, a single colony was isolated and confirmed on the respective media, incubated for 24–48 hours, and then transferred to Tryptic Soy Broth (TSB) for overnight growth. A portion (600 μl) of the TSB culture was saved in 20% glycerol and frozen at -80C. The sample type and corresponding farm were recorded in a spreadsheet to share with the farms. Findings revealed varying levels of coliforms and occasional positives for E. coli, L. monocytogenes, and Salmonella in both swab and soil samples, indicating potential risks for zoonotic contamination across different areas of the farm.

These results are correlated with metadata on climate conditions, and ultimately are shared with participating farms to guide improvements in food safety protocols. This surveillance work is critical for identifying early signs of contamination, supporting safer food production practices, reducing the likelihood of recalls, and ultimately protecting public health.