P-015. Microbiological Analysis of Composts Produced in California as an Amendment for Agricultural Production

M. W. Shepherd, Jr., S. D. Heringa, J. Kim, R. Singh, X. Jiang;
Clemson Univ., Clemson, SC.

Raw or inadequately composted animal wastes have been identified as sources of foodborne pathogen contamination in leafy greens. The goal of our study was to determine if composting vegetable wastes alone, or with manure, would effectively eliminate foodborne pathogens. Of the four facilities in California, two composted green wastes with poultry litter, one composted green wastes with dairy manure, and one composted green wastes with municipal solid wastes. At these facilities, composite compost samples were taken from surface and interior locations of minimally and extensively composted heaps. The analysis of compost samples included enumeration of coliforms and Escherichia coli populations, pH and moisture content determinations, and enrichment for the pathogens Salmonella, Listeria monocytogenes, E. coli O157:H7 and shiga-toxin producing E. coli (STEC). Additionally, temperatures of the compost heaps were recorded. Coliforms were detected in 100% of the surface compost samples collected from the compost heaps. Internal samples from minimally and extensively processed composts contained populations of coliforms and E. coli ranging from not detectable through ca. 5 log cfu/g and not detectable through ca. 4 log cfu/g, respectively. Over the 93 compost samples, Salmonella was detected in 7 samples (7.5%), including the surface of an early stage compost of a dairy manure-based heap and a late stage compost of a heap composted with poultry litter. L. monocytogenes was detected in the starting materials of a green waste compost and E. coli O157:H7 was not detected in any compost sample analyzed. Among 59 E. coli isolates analyzed by PCR, no STEC was identified. Results revealed that indicator and pathogenic bacteria may remain viable on the compost surface for weeks to months. Data from the finished California compost samples generally indicate that extended composting results in the inactivation of pathogens inside of the body of compost heaps.