An official website of the United States government.
Animal manure which is frequently used as a fertilizer for growing vegetables and fruits, commonly contains enteric pathogenic microorganisms. These pathogens can contaminate produce during growth in soil. Composting manure can kill harmful microorganisms at specific temperatures and holding times; however, these conditions have not been fully validated. <P>The objectives of this project are: <OL> <LI> To determine the inactivation conditions for Salmonella and Listeria monocytogenes in manure compost in the controlled environment of a laboratory bioreactor; <LI> To determine the survival and growth of avirulent strains of Escherichia coli O157:H7, Salmonella spp., and Listeria innocua during the curing of compost produced on a dairy farm using typical aerated static pile composting methods; (<LI> To determine the fate of E. coli O157, Salmonella and L. innocua in compost contaminated with these microbes during storage; <LI> To isolate competitive microorganisms that are inhibitory to foodborne pathogens and determine if their antagonistic activity can reduce pathogen levels in compost; (<LI> To conduct a survey of the practices commonly used to produce compost on small and medium size farms and determine the prevalence of E. coli O157:H7, Salmonella, and Listeria monocytogenes in compost that will be used to grow fruits and vegetables, either conventionally or organically; <LI> To educate vegetable and fruit growers in Georgia and South Carolina on how to produce and apply compost that is microbiologically safe. This research and outreach project should provide microbiologically safer produce for consumers and microbiologically safer farm environments for agriculturaists.
Laboratory-scale studies will be conducted in a bioreactor to determine rates of thermal inactivation of Salmonella and Listeria monocytogenes during composting between 55oC and 77oC. Pathogens will be labeled with a green fluorescent protein (GFP) marker to enable their enumeration on selective media. Manure compost-associated competitive microorganisms that are inhibitory to Salmonella, E. coli O157:H7 and Listeria monocytogenes will be isolated, screened by in vitro disk agar spot assays, and identified, then evaluated for their ability to control or restrict growth of these pathogens at different temperatures in compost piles and manure. On-farm composting studies using the aerated static pile method with avirulent GFP-labeled Salmonella, E. coli and L. innocua, will involve placing labeled bacteria in compost in nylon bags and sampling periodically to determine rates of inactivation. Temperatures at various locations throughout the compost pile will be monitored continuously to correlate temperature with rates of microbial inactivation. An on-farm microbiological survey of composting piles will be done involving approximately five dairy and five poultry farms in South Carolina and Georgia. Compost will be sampled at different locations in the pile and assayed for E. coli, E. coli O157:H7, Salmonella and Listeria monocytogenes. Temperatures at each sampling site will be determined prior to sampling and correlated with results of microbiological analyses. A questionnaire will be completed for each farm to identify correlations between composting practices and pathogen contamination. Extension specialists from South Carolina and Georgia will assimilate the best composting practices identified from the research component of this project and disseminate them through Field Day demonstrations that will include instructions on how to best construct and maintain compost piles to minimize pathogen contamination, as well as provide in-service training sessions for county agents, presentations at fruit and vegetable grower and organic growers annual conferences, post best practices on the Sustainable Agriculture Program website, and publish this information in trade newsletters and magazines.
<P>
Studies will identify best practices for producing compost from animal manure to reduce the risk contamination by bacterial foodborne pathogens like Salmonella, E. coli O157:H7 and Listeria monocytogenes.
<P>
A microbiological survey of composting operations on three poultry farms in South Carolina has been started. Composting operations encompassed windrow, static pile, and bin composting with either chicken carcasses or chicken litter serving as the major nitrogen source. Samples (500 g) were collected aseptically from different locations of the composting pile. Total bacterial counts in the compost ranged from log 5 to log 10 cfu/g while E. coli (a fecal indicator microorganism), ranged from <1 to log 5 cfu/g. E. coli, however, was detected most often on the surface of the pile. At the surface, moisture contents and temperatures were also lower while mesophilic bacterial populations were higher. To date, several compost piles have tested positive for either Salmonella or Listeria (detected by selective enrichment broths followed by immunomagnetic bead separation). Periodic sampling of these sites along with others is to be continued and these data will be used to characterize the prevalence of contamination by these pathogens under defined composting practices. Field sites have also been prepared for on-farm composting demonstrations (Georgia) and controlled field trials (South Carolina). Bioreactor studies have been initiated to investigate the influence of compositional parameters on heat profiles and subsequent inactivation of Salmonella spp.
<P>
Animal manure frequently contains enteric microorganisms that are human pathogens. This study will clarify the composting conditions needed for pathogen inactivation as well as screen the prevalence of pathogen contamination in compost of small-scale operations.