Comparison of Pathogen Detection Methods in Compost and Compost Characteristics as Potential Predictors of Pathogen Regrowth
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Improperly thermally treated compost can allow human pathogens to survive. Pathogens can regrow in finished compost due to recontamination or incomplete pathogen-kill. U.S. Environmental Protection Agency's (EPA) and U.S. Composting Council's (USCC) methodologies were compared to recover populations of inoculated non-pathogenic E. coli and pathogenic Salmonella spp. from finished compost. Two immunomagnetic separation (IMS) techniques were additionally compared for the rapid recovery of inoculated pathogenic E. coli O157:H7. Twenty-nine point-of-sale composts were obtained from 19 U.S. states. EPA methods recovered more (generic E. coli, p=0.0001) or statistically equal (Salmonella, p=0.27) amounts of inocula compared to USCC methods. Both IMS techniques identified with 3-4% false negatives among replicates. Physicochemical parameters of compost were tested as predictors of Salmonella and O157:H7 regrowth in finished compost. Salmonella and O157:H7 populations increased over three days in 48% and 52% of compost samples, respectively. No physicochemical measurements could predict the regrowth of Salmonella or O157:H7.