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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE Title: Antimicrobial activity of essential oils against E. coli O157:H7 in organic soil

Authors
item Yossa, Nadine -
item Patel, Jitu
item Millner, Patricia
item Lo, Martin -

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2010
Publication Date: May 6, 2010
Repository URL: http://hdl.handle.net/10113/44475
Citation: Yossa, N., Patel, J.R., Millner, P.D., Lo, M. 2010. Antimicrobial activity of essential oils against E. coli O157:H7 in organic soil. Food Control. 21(11):1458-1465.

Interpretive Summary: Pathogens (e.g., E. coli O157:H7) in soil can be a significant source of produce contamination prior to harvest in both conventional and organic production systems. There are currently no antimicrobial treatments for soil. Organic producers are increasingly using natural pesticides such as essential oils, instead of synthetic pesticides, to control insect pests. Since there is no information about the antimicrobial activity of these oils, we conducted studies to assess 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 vinegar (acetic acid) at 0.5 percent, 1.0 percent, 1.5 percent and 2.0 percent, were mixed with organic, sandy soil and inoculated with different strains of E. coli 0157:H7. Soils were sampled on days 1, 7 and 28 to determine E. coli survival. E. coli populations in soil were reduced by up to 5 orders of magnitude after 24 h at room temperature (22°C) with 2 percent cinnamanaldehyde, Ecotrol, Sporan or vinegar; overall, cinnamaldehyde was superior to other treatments in reducing E. coli O157:H7 populations in soil. In contrast, the antimicrobial effect of eugenol was not evident at either the 0.5 percent or 2 percent level. In general, increases in essential oil concentrations corresponded to reduced survival of E. coli O157:H7 with all oils used in this study. Results show the potential for oils to effectively reduce E. coli O157:H7 populations in soil. Interventions that significantly reduce E. coli in soil prior to or during crop growth could help producers in controlling potential contamination of fresh organic produce and reduce produce related outbreaks.

Technical Abstract: 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. In this study, we examined the antimicrobial activity of several essential oils against E. coli 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 percent, 1.0 percent, 1.5 percent and 2.0 percent, were mixed with organic, sandy soil and inoculated with five different strains of E. coli 0157:H7 separately. Soils were incubated at room temperature and samples obtained at 1, 7 and 28 days were enumerated to determine survival. E. coli populations in soil were reduced by up to 5 log CFU/g after 24 h incubation at room temperature (22 deg C) with 2 percent cinnamanaldehyde, Ecotrol, Sporan or vinegar. In contrast, the antimicrobial effect of eugenol was not evident either at 0.5 percent or 2 percent level. E. coli O157:H7 populations were reduced by up to 4 log CFU/g after 7 days of incubation with 1 percent cinnamaldehyde, 1.5 percent, vinegar, 2 percent Ecotrol or Sporan at 1.5-2 percent. Overall, E. coli 0157: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 populations in soil. Reduction in E. coli O157:H7 by eugenol was not significantly different from control. In general, increases in essential oil concentrations corresponded to reduced survival of E. coli O157:H7 with all oils used in this study. Results show the potential for oils to effectively reduce E. coli O157:H7 populations in soil. Interventions that significantly reduce survival of E. coli in soil prior to or during crop growth while simultaneously contributing to crop pest control could offer producers promising options to reduce potential contamination of fresh organic produce inadvertently contaminated by soil.

Last Modified: 9/22/2014
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