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United States Department of Agriculture

Agricultural Research Service

Title: Studies to Select An Appropriate Non-Pathogenic Surrogate Escherichia Coli Strain for Potential Use in Place of Escherichia Coli O157:h7 and Salmonella in a Pilot Plant Studies

Authors
item Annous, Bassam
item Riordan, Denise - FORMER ARS EMPLOYEE
item Sapers, Gerald

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 6, 2004
Publication Date: February 5, 2005
Citation: Annous, B.A., Riordan, D., Sapers, G.M. 2005. Studies to select an appropriate non-pathogenic surrogate escherichia coli strain for potential use in place of escherichia coli o157:h7 and salmonella in a pilot plant studies. Journal of Food Protection. 68(2): 282-291.

Interpretive Summary: This laboratory is engaged in pilot plant studies characterizing the efficacy of various washing and sanitizing treatments in reducing populations of pathogenic microflora, specifically Escherichia coli 0157:H7 and Salmonella, on fruit. However these organisms cannot be introduced to the pilot plant in its present configuration because of concerns for operator safety. Therefore, non-pathogenic E. coli strains have been employed as surrogate organisms. The aim of the present study is to compare the survival characteristics of sixteen non-pathogenic strains with those of two E. coli 0157:H7 and two Salmonella strains. All four pathogenic strains were previously associated with foodborne outbreaks in produce or apple cider. In this study the growth profiles and thermal resistance of the strains were examined following incubation in five typical growth media. Ongoing studies at this laboratory are investigating novel methods of decontaminating fruit with H2O and other antimicrobial agents, therefore, the rate of attachment of these strains to apple surfaces, and subsequent reduction by washing in a H2O2 solution, were investigated. Non-pathogenic surrogate strains were identified with behavior closely resembles that of the pathogens tested under the parameters examined. These surrogates will be useful for validating the efficacy of intervention steps in reducing E. coli O157H:7 and Salmonella populations in processing environment, but will not pose a health hazard to operators involved.

Technical Abstract: Often, in the interests of operator safety, it is necessary to use surrogate organisms in place of pathogens in large-scale food challenge trials. The behavior of potential surrogates should be characterized to ensure that they closely mimic the behavior of the target pathogen under the challenge conditions. In this study the survival characteristics of 16 non-pathogenic Escherichia coli strains were compared to 2 E. coli 0157:H7 strains and 2 Salmonella strains (previously associated with foodborne disease outbreaks in produce or apple cider). pH at stationary phase, growth characteristics, heat resistance at 60C were obtained for each strain following growth in five different media. In addition, the level of attachment to apple surfaces and resistance to hydrogen peroxide decontamination treatments were assessed for each strain. Few differences in growth characteristics or pH were evident between the non-pathogenic strains and E. coli 0157:H7, though higher final pH values were seen with Salmonella strains (P<0.05). E. coli 0157:H7 and Salmonella strains were not significantly different for any of the growth characteristics measured, or in the levels of attachment to apple surfaces and resistance to hydrogen peroxide, however, E. coli 0157:H7 was significantly more resistant to heat than Salmonella (P<0.05). E. coli O55:97.0152 appears to be a good surrogate candidate, with survival characteristics which are similar to E. coli 0157:H7 under these challenge conditions. A less heat resistant strain of E. coli, perhaps E. coli NRRL 766, must be used when attempting to reproduce the heat resistance of Salmonella. These data will be useful in validating the efficacy of intervention steps in reducing E. coli 0157:H7 and Salmonella populations in processing environments.

Last Modified: 12/22/2014
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