Submitted to: American Society for Microbiology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: December 14, 2004
Publication Date: June 5, 2005
Citation: Ingram, D.T., Scheurell, S.J., Millner, P.D. 2005. Evaluation of two compost tea brewing methods for the ability to propagate foodborne pathogens. American Society for Microbiology Meeting, June 5-9, 2005, Atlanta, GA.
Certain cultural practices have the potential to modify the native microbial flora of fruit and vegetable surfaces and therefore should be examined for their impacts on foodborne pathogens. Compost tea (CT), prepared as aerated or non-aerated watery extracts from compost, is used by both organic and conventional producers. This tool has the reputation among growers of being a cost-effective, biologically-based control for a number of foliar and root diseases, possibly with plant-growth-promoting activity. One explanation for the efficacy of CT is that the native phylloplane microflora is overwhelmed by a diverse multitude of microbes that competitively exclude and/or inhibit phytopathogens. However, CT may be a source of foodborne pathogens if the ingredients or the process are not properly controlled. In this study, we evaluated the potential of two compost tea systems (aerated tea and non-aerated tea) to support the growth and survival of foodborne pathogens. Compost feedstock, spiked with marked strains of E. coli O157:H7, Salmonella Enteritidis and Enterococcus spp., was used to prepare CT with different temperature and nutrient conditions. We determined the concentration of these pathogens throughout the production of both aerated CT (24hr) and non-aerated CT (8.5 days). Where nutrients were used to brew the tea, the resulting pathogen concentrations exceeded inoculated levels substantially. The inoculated pathogens and indicators remained undetectable in all CT to which nutrients were not added. Results show that readily metabolized carbon-based nutrient sources support the growth of human pathogens even when dissolved oxygen ' 6 ppm. Therefore we conclude that the use of supplemental nutrients to produce CT will require additional testing of the final product to ensure the absence of human pathogens. This is consistent with one of the ten Compost Task Force recommendations accepted by the National Organic Standards Board on October 13, 2004.