Environmental Effects on the Growth or Survival of Stress-Adapted Escherichia Coli 0157:H7 and Salmonella spp. in Compost

Raw or inadequately composted animal manure has been considered as a potential source of pre-harvest contamination of fresh produce. Composting, as a practical way for waste management on farm, can inactivate human pathogens, but the outcome can be affected by many environmental factors. Therefore, there is a need for developing composting guidelines and standards to apply to a wide range of conditions. <P>
In this proposed study, we hypothesize that the extended mesophilic composting phase may induce heat-shock response in human pathogens, which become resistant to subsequent lethal temperatures during thermophilic phase of composting. Other sub-optimal conditions, such as slow heat-up of compost, low moisture contents and carbon to nitrogen ratio (C:N) in compost, may also enhance the survival of stress-adapted human pathogens during composting. Therefore, our first approach will determine the thermal resistance of heat-adapted cultures in compost at elevated composting temperatures by simulating early stage of on-farm composting. Due to nonlinear reduction of pathogens by composting, a mathematical model will be developed to describe thermal inactivation of stress-induced pathogens in compost under non-isothermal conditions. <P>
Second approach will apply indigenous microorganisms as a secondary treatment to prevent pathogen regrowth in cured compost. <P>
Finally, we will improve the sensitivity of pathogen detection from compost by using bacteriophages to suppress indigenous microflora, and Pathatrix® system to concentrate the target pathogens from enrichment cultures. <P>
We expect the results from this proposed study will provide scientifically validated composting guidelines to compost industry, and thereby to reduce contamination of fresh produce by pathogens in compost.