P3-81 Evaluation of Four Assessment Methods Used to Identify Foodborne Pathogens Prior to the Harvest of Fresh Produce

Wednesday, July 12, 2017
Exhibit Hall (Tampa Convention Center)
Paula Rivadeneira , University of Arizona , Yuma , AZ
Martha Ruedas , University of Arizona , Yuma , AZ
Teresa Reyes , University of Arizona , Yuma , AZ
Elene Stefanakos , University of Arizona , Yuma , AZ
Robert Buchanan , University of Maryland, Department of Nutrition and Food Science and Center for Food Safety and Security Systems , College Park , MD
Introduction: Within seven days before harvest, produce growers conduct foodborne pathogen testing of their crops to ensure food safety. Currently, there is no standardized pattern to collect these samples.

Purpose: We tested the efficacy of four sampling patterns in produce fields in southern Arizona to determine which is best at identifying foodborne pathogens.

Methods: [1.] Using random, stratified random, Z-pattern, and targeted preharvest assessment techniques, we collected 747 leafy green samples from 10 fresh produce fields 24 to 72 h after they tested positive for Shiga toxin-producing E. coli (STEC) or Salmonella. [2.] We conducted a controlled blind trial by contaminating a romaine lettuce field with dairy cow manure tea inoculated with E. coli at 106CFU/ml. After 48 h, we collected blind samples using random, stratified random, and Z-pattern techniques. [3.] We conducted another controlled blind trial and collected the samples using the same three sampling patterns, but after only 12 h of overnight exposure.

Results: [1.] One field tested positive for Salmonella (one sample), E. coli O157 (one sample), and generic E. coli (four samples). Two other fields tested positive for generic E. coli (two samples each). The time lapse between the initial positive test results and our resampling of the field may have allowed environmental factors to eliminate pathogens. [2.] We did not recover E. coli during the first blind trial. [3.] We recovered two positive samples using the random sampling method, three using stratified random, and two using Z pattern. None of the sampling types performed better than the others, but the results indicated that ultraviolet radiation may have destroyed pathogens during our first two studies.

Significance: Our data indicate that preharvest sampling patterns do not differ in efficacy, and that environmental factors may play an important role in pathogen persistence, particularly in the southwest desert region.