Impact of Riparian Forests on the Prevalence of Non-Pathogenic Escherichia coli Contamination in Produce Fields

Introduction: Agricultural water and soils contaminated with animal feces are identified routes of produce microbial contamination. While fecal deposition by wild and domestic animals may facilitate the introduction of pathogens into the agricultural landscape, environmental conditions (i.e., soil properties, precipitation, and temperature) can constrain microbial survival and persistence in the pre-harvest environment. Limited data exists on the role of riparian forests bordering croplands, which provide natural habitat for wildlife, in fecal bacteria dispersal onto adjacent fields.

Purpose: The prevalence and distribution of generic Escherichia coli in proximity to riparian forest buffer zones in the pre-harvest environment were investigated.

Methods: Riparian forests and adjacent produce fields located along the Flint Creek (FC; n = 9) and the Hoosick River (HR; n = 10) were sampled between September and October 2012. E. coli was cultivated in samples collected from soil (n = 279), drag swab (n = 115), fecal (n = 157), and water (n = 20). Variances in the frequency of positive cultures were analyzed using a chi-square test. Isolates were confirmed by PCR and mdh gene sequencing.

Results: The overall prevalence of E. coli cultivated from all samples was 65% (372/571).  E. coli was widely distributed in all sample types collected from both field and forest sites in the two riparian zones: soil (53%, 149/279), drag swab (73%, 84/115), fecal (76%, 119/157), and water (100%, 20/20). HR riparian sites (forest and fields) were more likely to yield positive samples (79%, 219/276) compared to FC sites (52%, 153/142) (P < 0.007). In general, forest soils were significantly associated with E. coli compared to field soils in both riparian zones (P < 0.007).

Significance: In support of FSMA prevention-based standards, our study will be used to develop tools to provide science-based environment-specific recommendations for preventive strategies to mitigate microbial contamination risk in the pre-harvest environment.