Submitted to: Mid-Atlantic Composting Association
Publication Type: Abstract Only
Publication Acceptance Date: 4/28/2005
Publication Date: 9/22/2005
Citation: Ingram, D.T., Millner, P.D. 2005. Compost tea: Is it a potential on-farm source of foodborne pathogens?[abstract]. Mid-Atlantic Composting Association, USDA, ARS, BARC, September 22, 2005, Beltsville, MD.
Technical Abstract: Compost tea (CT), as distinct from compost pile leachate, is used by organic as well as some conventional growers to promote plant growth and suppress foliar and root diseases. We examined the potential for enteric bacteria to grow during both aerobic and anaerobic tea production, concurrent with the growth of a diversity of other aerobic microbes, which purportedly act to competitively exclude phytopathogens. The effects on the enteric bacterial populations of various commercial additives, such as unsulphured molasses, soluble kelp, humic materials and proprietary ‘nutrient solution’ preparations, used in on-farm production of CT, were evaluated. In the first series of experiments, a commercially available mature compost, which was inoculated with varying amounts of enteric pathogens and commercial additives, was used to produce aerobic CT. In a second series of experiments, both aerobic and anaerobic brewing systems were evaluated for their effects on the growth of enteric pathogens. In general, even low numbers of enteric foodborne pathogens grew in CT containing additives, but they remained undetectable in all CT to which nutrients had not been added. The often purported view among compost tea producers that the diversity of aerobic heterotrophs in compost is sufficient to inhibit growth of enteric pathogens when aerobic conditions are present was not supported by this data when soluble carbon additives were supplied. The use of soluble carbon sources during the production of CT has declined in the past year because of this type of result, however, alternative additives have emerged and their use can also lead to growth of enteric pathogens in CT. Careful sanitation and selection of all CT feedstock are necessary, including the selection of mature compost. Therefore, we conclude that the use of supplemental nutrients to produce CT necessitates testing of the final product under the circumstances of production to ensure the absence of enteric pathogens. This is consistent with one of the ten Compost Task Force recommendations accepted by the National Organic Standards Board on October 13, 2004: www.ams.usda.gov/nosb/meetings/CompostTeaTaskForceFinalReport.pdf