Foes on the Farm: Microbial Surveillance of Major Foodborne Pathogens in Delaware Agricultural Soils

• Ava Slaughenhoupt, Food Science, University of Delaware

• Kalmia Kniel, Animal and Food Sciences, University of Delaware

Agricultural soils contain a microbiome rich in microorganisms such as fungi, viruses, and  bacteria, some of which are pathogenic and dangerous to humans if consumed after coming in contact with raw agricultural commodities. These include Listeria monocytogenes, Salmonella species, and E. coli. While the majority of bacteria live naturally within the soil, pathogenic bacteria originating from the soil have been associated with many outbreaks due to consumption of fresh produce. Conducting surveillance within an area can help monitor the presence of these harmful pathogens, establish mitigation strategies, and educate growers on strategies to reduce risks with produce. Weekly surveillance on eight farms was conducted for the bacteria mentioned previously, analyzing irrigation water, soil, and swabs from processing/packing facilities. Samples were enumerated for E. coli and coliforms on Charm plates, on XLT-4 agar for Salmonella spp., and RAPID agar for Listeria spp. and L. monocytogenes. In addition, samples were saved for further processing of DNA and RNA analysis. Bacterial isolates were collected from positive samples of Listeria monocytogenes and Salmonella. These isolates will be serotyped and further studied. Salmonella spp. were the most prevalent across all Delaware soils, often found on produce containers and packing lines. Generic E. coli was detected most often on conveyor belts and packing tables, which could indicate animal or human contamination. Listeria monocytogenes was detected in cold storage areas due to its resistance to cold temperatures. Although food safety practices are in place, many do not account for the environmental resistance that harmful bacteria may have. Isolating bacterial colonies supports future studies and analysis to better understand the genetics of pathogenic bacteria. Surveillance promotes prevention and implementation of improved sanitation and cleaning practices for growers to better reduce risks associated with fresh produce, as well as a better knowledge of produce safety concerns.