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.