Purpose: The objectives of this study were to assess the natural occurrence of two major foodborne pathogens, Shiga Toxin-producing Escherichia coli (STEC) and Salmonella, in native pecan production and the influence of cattle grazing in such incidence.
Methods: Samples of soil, cattle feces, pecans (from the ground and harvested), and wild animal fecal swabs were collected from eight pecan production orchards (four cattle grazed and four without) at pre-harvest (two months before harvesting) and during harvest. Swabs from harvesting equipment surfaces were also collected during harvest. Isolation and detection of STEC and Salmonella were performed by enrichment, selective enrichment/plating, and multiplex PCR. Molecular typing of isolates was conducted by pulsed-field gel electrophoresis (PFGE).
Results: While both pathogens were detected in pecan production orchards, significantly (P < 0.05) higher numbers of STEC-positive samples were obtained. Salmonella was detected in pre-harvest (17%) and harvest (8%) soil samples from a non-grazed orchard as well as cattle feces (17%) in grazed orchards at pre-harvest; however, no Salmonella was detected in harvested pecans, regardless whether the orchards were grazed by cattle or not. Surprisingly, the percentages of STEC-positive pecans (from the ground or harvested) were not significantly different between grazed and nongrazed orchards, with 33% ground pecans and 5% harvested pecans from nongrazed orchards and 8.3% ground and 17.5% harvested pecans from grazed orchards tested positive for STEC.
Significance: The results of our research show the presence of human pathogens in native pecan production and the complicated contributing sources to such contamination, including sources other than cattle grazing.