P3-133 Simulation of Wildlife Fecal Contamination of Romaine Lettuce by Indicator Escherichia coli

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Saharuetai Jeamsripong, University of California-Davis, Davis, CA
Michele Jay-Russell, University of California-Davis, Davis, CA
Jennifer Carabez, University of California-Davis, Davis, CA
Edward Atwill, University of California-Davis, Davis, CA
Anne-laure Moyne, University of California-Davis, Davis, CA
Alexis Fisher, University of California-Davis, Davis, CA
Melinda Faubel, University of California-Davis, Davis, CA
Ronald Bond, University of California-Davis, Davis, CA
Melissa Partyka, University of California-Davis, Davis, CA
Linda Harris, University of California-Davis, Davis, CA
David Oryang, U.S. Food and Drug Administration, College Park, MD
Introduction: Foodborne disease outbreaks have been linked to enterohemorrhagic Escherichia coli (EHEC) contamination of fresh produce from domestic and wildlife sources.  Non-pathogenic generic E. coli strains may be used to monitor for potential fecal material in the fresh produce production environment. Indicator strains of generic E. colihave also been used to study bacterial transference and survival to plants under commercial experimental field conditions.

Purpose: The purpose of this study was to conduct applied real-world field research to determine the amount and persistence of generic E. coli that transfers onto Romaine lettuce following simulated contamination by wild animal defecation.  

Methods: Experimental field trials were conducted in the Salinas Valley, California following the U.S. Food and Drug Administration Quantitative Predictive Risk Assessment Model (QPRAM) protocol with modifications. Specifically, feces (chicken, rabbit, and pig) were inoculated with rifampicin-resistant generic E. coli to estimate the transfer, survival, and concentration on mature Romaine lettuce plants following foliar irrigation Negative binomial and linear regressions were used to assess contributing factors for prediction of bacterial contamination and to measure bacterial survival, respectively.

Results: Inoculated E. coli was recovered from a total of 182/196 (93%) lettuce heads following irrigation. A decreasing concentration (7.8 log reduction) was observed in 41 samples from the fecal pat to the 5-foot no-harvest zone. Age of scat, distance from scat, and distance from sprinkler heads were statistically significant with the magnitude of bacterial transference to lettuce in linear model (P < 0.05). All 288 spiked heads had detectable inoculated E. coli up to 10 days post-inoculation. Decimal Reduction Time (DRT) of bacteria in chicken and rabbit feces were 2.2 and 2.5 days, respectively, while the pig feces was unpredictable.

Significance: These data will enhance the effectiveness of good agricultural practices designed to protect leafy greens from microbial contamination due to animal intrusions.