Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: July 20, 2004
Publication Date: August 10, 2004
Citation: Ingram, D.T., Millner, P.D. 2004. Growth of foodborne pathogens during production of compost tea. [Abstract]. International Association for Food Protection. August 10-12, 2004, Phoenix, Arizona. p.2.
Compost tea (CT) is increasingly used in various cropping systems as a non-chemical foliar spray or soil drench to promote plant growth and suppress disease. We examined the potential for foodborne pathogen bacteria to grow during certain tea production practices. This study addressed the influence of pre-packaged, commercial additives, such as unsulphured molasses, soluble kelp, humic materials and proprietary 'nutrient solution' preparations on the survival and growth of E. coli O157:H7, Salmonella enterica serovar Typhimurium and Enterococci faecalis during the tea production. Commercially available, mature compost with undetectable numbers of target bacteria was used to produce CT aerobically (dissolved oxygen > 7 ppm) in 18.9L containers in 24 hours. Aliquots of compost were inoculated or not with small amounts of target strains (pre-conditioned for growth on compost) and placed into mesh retainers which were immersed in the brewing bucket with dechlorinated tap water. Test batches included varying amounts of inoculum and commercial additives. In general, target foodborne pathogens grew in CT that contained additives, and did not grow in the absence of additives. Results show that soluble carbon additives in CT production promote growth from even small concentrations of pathogens present in a matrix containing large concentrations of heterotrophic bacteria. The concept that the diversity of heterotrophs in compost is sufficient to inhibit growth of the target pathogens was not supported by this data when soluble carbon additives were supplied. The benefits of soluble carbon supplements in CT warrants further study.