Purpose: Here studies evaluated generic E. coli and fecal coliforms (FC) as indicators of contamination associated with wildlife fecal material on the surrounding plants and soil within a measured buffer zone.
Methods: Composite leaf (25 g) and soil (100 g) samples were collected from fields in Delaware and California from the summer 2015 to spring 2016. Sampling occurred around the buffer circumference randomly starting at 10 ft from the identified fecal contamination, and moving inward at 5 distances. A total of 5 pooled leafy green and 5 pooled soil samples were analyzed for generic E. coli and FC at each fecal event.
Results: In Delaware, no generic E. coli was detected except at 7ft (3.2 x102 CFU/sample) in soil (1/15). Fecal coliforms were detected in lettuce (6/20) and soil (9/19), ranging from (3.5 x 102 to 1.7 x 104 CFU/sample). In California, generic E. coli was detected in soil (2/15) samples only at 0 ft (3.5 x 105 CFU/sample) and 1 ft (3.4 x 105 CFU/sample) from fecal material. Fecal coliforms were detected in lettuce (3/13) and soil (5/15), ranging from (9.5 x 103 to 1.1 x 106 CFU/sample). In both regions, generic E. coli was undetectable on lettuce and spinach samples from all 5 distances (0/29) and recovery of FC was too sporadic to determine a significant effect by distance.
Significance: At each fecal event, generic E. coli and FC were enumerated in surrounding leafy greens and soil within and outside of the 5-ft no-harvest buffer zone, suggesting that harvesting leafy green in close proximity to fecal contamination may pose a potential food safety hazard.