Purpose: The objective of this study was to determine and compare the persistence of important produce-related STEC and Salmonella serotypes/serovars in various types of animal manures which commonly contaminate vegetable fields.
Methods: Two Rifampicin resistant-bacteria cocktails, one consisting of six Salmonella serovars (Typhimurium, Montevideo, Anatum, Javiana, Branderup, and Newport) and the other consisting of five STEC serotypes (O103, O104, O111, O145, and O157), were each applied to manures of domestic cattle, deer, wild pig, raccoon and waterfowl at level of 103 to 104 CFU/g feces, respectively. The inoculated manures were stored at room temperature (22°C), and tested periodically for Rifampicin resistant STEC and Salmonella. Molecular typing (PCR and PFGE) of recovered bacterial colonies were done to determine the bacterial serotypes/serovars surviving longest in manure.
Results: Under 22°C, STEC survive the longest in cattle feces for 12 months, followed by raccoon feces (10 months), deer feces (6 months), pig feces (4 months), and waterfowl feces (2 months). In comparison, Salmonella survived same long in feces of cattle, deer, and waterfowl, but lived longer in raccoon (12 months) and pig feces (5 months). Among the serotypes/serovars tested, STEC O104, Salmonella Anatum and Javiana totally out-competed others in feces of cattle, deer, raccoon and waterfowl. Salmonella Branderup survived as well as Javiana in pig feces for 5 months.
Significance: The study justifies no harvest stipulations and one year prohibition of cultivating on fields when incompletely composted or non-thermally treated manure has been applied, and facilitates understanding of how feces type may affect pathogen fate in the environment.