Potential role of a free-living nematode, Caenorhabditis elegans, in preharvest contamination of fruits and vegetables with Salmonella Newport
Kenney, Stephen Jeffrey
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Caenorhabditis elegans, a free-living nematode found in soil, has been shown to ingest human enteric pathogens, thereby potentially serving as a vector for preharvest contamination of fruits and vegetables. Factors affecting the ability of C. elegans to harbor pathogens in its gut and transport them to the surface of fruits and vegetables were studied. The effects of temperature and relative humidity on the survival and growth of Escherichia coli O157:H7, Salmonella Poona, and Salmonella Newport were assessed. Populations of ingested pathogens remained constant at 4°C, decreased significantly at 20°C, and increased significantly at 37°C within 3 days. Populations of S. Newport decreased by up to 3.44 log10 cfu/worm when infected worms were incubated at 20°C and 33% relative humidity. The efficacy of cleaners commonly used in food processing plants in killing ingested pathogens was influenced by desiccation of worms. Cleaners and sanitizers were more effective in significantly (P = 0.05) reducing the number of ingested S. Newport, but none of the test cleaners or sanitizers eliminated the pathogen at all temperature/relative humidity combinations. C. elegans migrates to bovine manure, turkey manure, composted bovine manure, composted turkey manure, and manureamended soil inoculated with S. Newport, as well as uninoculated lettuce, strawberry, and carrot on an agar medium. C. elegans survived and reproduced in turkey and bovine manures, and the presence of S. Newport did not adversely affect its behavior. When a 5-cm column of soil containing C. elegans was placed on top of bovine manure or bovine manure compost inoculated with S. Newport, which in turn was topped with a piece of lettuce, strawberry, or carrot, the pathogen was detected on the surface of the produce within 1 day. The pathogen was rarely detected on produce when C. elegans was not present in the soil. In field settings, the incidence of C. elegans ingesting human pathogens and transporting them to preharvest fruits and vegetables may be low, but on occasion this phenomenon may occur. Results from these studies reinforce the importance of sanitizing produce prior to consumption.