Purpose: The aim of this study was to assess the natural occurrence of human pathogens, Shiga toxin-producing Escherichia coli (STEC), and Salmonella, in native pecan production fields.
Methods: Samples of soil, cattle feces, pecans, and wild animal fecal swabs were collected from different sites of three pecan production fields at preharvest (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 PCRs. Molecular typing of isolates was conducted by pulsed-field gel electrophoresis (PFGE).
Results: At preharvest, Salmonella. was detected from 22%, 17%, and 18% of soil, cattle feces and wild animal swabs, respectively. However, none was detected from samples collected during harvest except 1 of 16 equipment surface swabs. Similarly, STEC were detected at preharvest from 22%, 100%, and 45% of soil, cattle feces and wild animal swabs, respectively. During harvest, these numbers were 22, 50%, and 50%, respectively, while 2 of 16 equipment surface swabs were positive for STEC. None of the harvested and bagged pecans were tested positive for either pathogen; however, STEC were isolated from 5 samples of broken pecans that had been excluded from bagging. Identical PFGE patterns were observed between STEC isolates from soil and cattle feces, and broken pecan and one of the harvesting equipment surface swabs.
Significance: This study showed the presence of human pathogens in pecan production fields and harvesting equipment, highlighting the need for the development of mitigation strategies starting from the production field to control potential human pathogen contamination of pecans.