MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE
Title: Biocontrol of E. coli O157:H7 in organic soil using essential oils
Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: February 17, 2010
Publication Date: September 17, 2010
Citation: Yossa, N., Patel, J.R., Millner, P.D., Lo, M. 2010. Biocontrol of E. coli O157:H7 in organic soil using essential oils [abstract]. Annual Meeting of the Institute of Food Technologists. PO38-59.
Soil can be a significant source of preharvest contamination of produce by pathogens. Demand for natural pesticides such as essential oils for organic farming continues to increase. Antimicrobial activity of essential oils in vitro has been well documented, but there is no information about their efficacy in soil. We examined the antimicrobial activity of several essential oils against E. coli O157:H7 in soil. Two essential oils (cinnamaldehyde and eugenol), two bio-pesticides (Ecotrol and Sporan) containing essential oils, and an organic acid (acetic acid) at 0.5%, 1.0%, 1.5% and 2.0%, were mixed with organic soil and inoculated with five different strains of E. coli O157:H7 separately. Soils were incubated at room temperature (22°C) and samples obtained at 1, 7 and 28 days were enumerated to determine survival. E. coli O157:H7 populations in soil were reduced by up to 5 log CFU/g after 24 h incubation at room temperature with 2% cinnamanaldehyde, Ecotrol, Sporan or vinegar. In contrast, the antimicrobial effect of eugenol was not evident either at 0.5% or 2 % level. E. coli O157:H7 populations were reduced by up to 4 log CFU/g after 7 days of incubation with 1% cinnamaldehyde, and 1.5%, vinegar. Reduction in E. coli O157:H7 by eugenol was not significantly different from control. Overall, E. coli O157:H7 strain 4406 was the most sensitive of all the five strains tested and cinnamaldehyde was superior to other treatments in reducing E. coli O157:H7 in soil. In general, E. coli O157:H7 populations in soil reduced with an increase in essential oil concentrations.
Results show the potential for oils to effectively reduce E. coli O157:H7 populations in soil. Interventions that significantly reduce E. coli O157:H7 in soil while simultaneously contributing to crop pest control could offer producers promising options to reduce potential contamination of fresh produce inadvertently contaminated by soil.