P3-126 The Effects of Contaminated Irrigation Water on Bacterial Persistence and Transmission of Coliforms on Tomatoes

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Patrick Spanninger, University of Delaware, Newark, DE
Krystal Shortlidge, University of Delaware, Newark, DE
Angela Marie Ferelli, University of Delaware, Newark, DE
Rachel Brown, University of Delaware, Newark, DE
Sarah Markland, University of Delaware, Wilmington, DE
Kalmia Kniel, University of Delaware, Newark, DE
Introduction: Irrigation water used in the production of tomatoes has been identified as a potential source of contamination. Current metrics are available for irrigation water; however, there is a gap in the scientific data assessing bacterial persistence following use of poor irrigation water.

Purpose: The purpose of the field trial was to determine the correlation between bacterial contamination in water and coliform and Escherichia coli presence on fruit at harvest.

Methods: Hybrid tomatoes BHN-602 (186 plants) were grown in 12 plots from June-August. Ten days prior to harvest, plants were irrigated with bovine manure-contaminated water at 4 levels (0, 100, 1000 and 10000 coliforms/ml). Fruit samples (n = 9/day/level) were randomly selected prior to, immediately following inoculation, and at days 1, 3, 5, 7, and 10 post-inoculation. Total coliforms and E. coliwere enumerated on TBX agar and by MPN using colilert.

Results: There were statistical differences in the persistence of coliforms (log/g of fruit) on days 3 (P < 0.0001) and 5 (P < 0.0174) following a single contamination event regardless of inoculation load. Samples taken prior to contamination had a significantly lower log coliform/g count (P < 0.0001). The overall greatest bacterial amount (4.13 log/g on day 1) recovered was from fruit irrigated with water at 10000 coliforms/ml. At day 10 all fruit from control or test plots had averages of 2.6 ± 0.39 log coliforms/g, likely influenced by rain at day 3 and proximity to road and woods. E. coli were absent from control plots before inoculation and present at 4.0 log MPN E. coli on day 10. An average of 3.28 ± 0.37 MPN E. coli were detected on fruit after inoculation despite the level of coliforms in contaminating irrigation water.

Significance: This data suggests that field trials in the mid-Atlantic region monitoring bacterial levels in irrigation water and proximity to roads and woods are useful in learning about the presence/absence of contaminating-bacteria on tomatoes at harvest.