Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 6, 2011
Publication Date: N/A
Interpretive Summary: Recent increases in foodborne illness outbreaks from consumption of contaminated fresh produce have increased concerns and interest in implementing treatment technologies that can reduce potential contamination from manure-borne pathogens. Among the treatment technologies currently available, thermophilic composting is recognized as a well-established practice that, when properly conducted, can significantly reduce the numbers of pathogens present in raw manure. Nonetheless, many livestock and poultry producers simply stack manure in piles until weather and time permit direct land application on-farm or export off-farm because they do not have the time, staff or economic incentive to compost manure according to prescribed protocols. However, with a few simple modifications, on-farm stacked manure piles can be managed to promote a more extensive zone of destructive internal temperature, more like that achieved by intensively managed composting practices. By attending to the conformation of the pile and utilizing on-farm resources like old straw, old hay, sawdust, or existing cured compost, an increased zone of aerobic thermophilic decomposition can be achieved, resulting in substantial reductions in pathogen loads. We evaluated the efficacy of several minimal management options for on-farm composting using a commonly available amendment, straw, to modify and/or insulate bovine manure piles to enhance self-heating temperatures to reduce concentrations of E. coli, Salmonella enterica, and Listeria monocytogenes. The survival and die-off of a nonpathogenic E. coli strain that is a high temperature tolerant surrogate for E. coli O157:H7, Salmonella Senftenberg, S. Typhimurium, and two strains of Listeria monocytogenes were evaluated for 28 days in manure pile treatments. The inoculated E. coli and salmonellae were reduced from initial concentrations of 8.0 to 9.0 log10 cfu (colony-forming units) per gram dry weight of manure compost (gdw) to undetectable levels (less than1.66 log10 MPN (Most Probable Number) per gdw) within the first 7 days in all straw-amended piles; 3-4 log reductions were obtained in piles containing only manure. Similiarly, L. monocytogenes concentrations were reduced from 6.62 log10 cfu per gdw to undetectable after 14 days in straw-amended piles; pathogens survived in piles containing only manure for 28 days. Decreases in pathogen population corresponded closely with exposure to pile temperatures above 45 deg C for more than 3 days. These results show that use of straw to increase aeration, self-heating capacity, and heat retention within the bulk mass areas of bovine manure piles provides producers a minimal management option for composting that will enhance pathogen die-off and thereby reduce risk of environmental spread when manure is applied to land.
Technical Abstract: Persistence of pathogenic bacteria such as E. coli O157:H7, Salmonella spp., and Listeria monocytogenes in bovine feces and contaminated soils is an important risk factor in perpetuating the initial infection as well as re-infection of cattle and dissemination of pathogens throughout agricultural landscapes. The latter spread has been implicated in field contamination of fresh produce. Various manure treatments to reduce pathogen concentrations are available to producers but are sometimes considered burdensome in terms of the time required for management. This report compares the effect of four bovine manure pile management options on the die-off of a non-toxigenic E. coli O157:H7 surrogate, and Salmonella Senftenberg and S. Typhimurium as well as two strains of Listeria monocytogenes. Manure treatment options reflect minimal changes in the way the manure piles are constructed using a commonly available addition, straw. In this study, bacterial strains were conditioned on bovine solids to avoid culture shock transition from laboratory to real-world manure environments. Vented sample cassettes containing spiked bovine manure were implanted at top, middle, and bottom loci within four different manure pile configurations and temperatures were monitored continuously during static, self-heating of piles for 28 days. Results show that the inoculated E. coli and salmonellae were reduced from initial concentrations of 8.0 to 9.0 log10 cfu per gdw to undetectable levels (less than 1.77 log10 MPN per gdw) at the 25-30 cm depths within the first 7 days in all pile loci except those of the manure-only pile in which 3-4 logs of reduction were obtained. No L. monocytogenes initially present at 6.62 log10 cfu per gdw were recovered from any of the straw-amended pile loci after 14 days in contrast with the manure-only pile in which this pathogen was recovered even at 28 days. Pathogen population declines corresponded to exposure to temperatures above 45 deg C for more than 3 days. The use of straw to increase aeration, self-heating capacity, and heat retention within the bulk mass areas of bovine manure piles provides producers a minimal management compost option that enhances pathogen die-off and thereby reduces risk of environmental spread when manure is applied to land.