P3-36 Microbial Survey of Surface Water Used for Fresh Produce Crop Irrigation in Pennsylvania

Wednesday, July 25, 2012
Exhibit Hall (Rhode Island Convention Center)
Audrey Draper, The Pennsylvania State University, University Park, PA
Stephanie Doores, The Pennsylvania State University, State College, PA
Hassan Gourama, The Pennsylvania State University, Reading, PA
Luke LaBorde, The Pennsylvania State University, University Park, PA
Introduction: Foodborne illness outbreaks linked to contaminated irrigation water from surface sources has created a need for improved farm food safety practices. Although there are no national legally enforced standards for microbial safety of irrigation water for growing produce crops, several government and commodity groups have developed their own surface water guidelines.

Purpose: The purpose of this study was to survey microbial indicators and select human pathogens in surface waters used for irrigation of fresh produce crops in Pennsylvania, compare these levels to current surface water guidelines, and determine if indicator microorganisms reliably predict the presence of pathogens.

Methods: Over the course of 2 years, 153 1-liter samples were collected from 39 farms at 3 times during the growing season. Data were collected for 6 physical attributes (conductivity, turbidity, pH, dissolved oxygen, air and water temperature), 14 environmental characteristics (including source type, precipitation 0 and 3 days before sampling, adjacent animal activity, degree of sunlight exposure), 5 indicator organisms (Enterobacteriaceae, coliforms, fecal coliforms, E. coli, and enterococci) and 2 pathogens (E. coli O157:H7 and Salmonella).

Results: Among all samples collected, 61% exceeded EPA recreational water and California leafy greens surface water limits for E. coli (126 CFU/100ml), 67% exceeded GlobalGap limits for fecal coliforms (1000 CFU/100ml), and 51% exceeded EPA standards for enterococci (33 CFU/100ml). E. coli O157:H7 and Salmonella were not detected in any samples using two different plating techniques. Statistical analysis of combined 2-year data showed significant (< 0.05) effects of certain physical attributes and environmental characteristics on E. coli, coliform, Enterobacteriaceae, and enterococci although significance of individual effects varied between years.

Significance: Microbial indicator levels varied greatly between farms and sampling times. Despite frequent failures to meet established water standards, indicator microorganisms did not reliably predict the presence of human pathogens as determined by plating techniques. The utility of microbial indicators to predict farm food safety risks must therefore be further examined.