Location: Produce Safety and Microbiology ResearchTitle: Diverse Shiga toxin-producing Escherichia coli-specific bacteriophages exist in goat feces and the surrounding environments on an organic, produce-growing farm in Northern California, USA
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/15/2019
Publication Date: N/A
Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) contamination on produce is primarily associated with ruminant feces, which can result in severe foodborne illness. Although numerous STEC-specific bacteriophages (phages) have been isolated from cattle feces, the presence of STEC-specific phages and any correlation with O157 and the top 6 non-O157 STECs (the top 7 STECs) in goat feces has not been thoroughly investigated. The objective of this research was to investigate the prevalence and diversity of the top 7 STECs and STEC-specific phages in ruminant feces and surrounding environments on an organic produce-growing farm. One sample each from 3 sites (goat feces, cattle feces, and soil) was collected monthly for 6 months (soil was collected for 5 months; n=17). Individually, samples were tested for STEC using culture and PCR-based methods and STEC-specific phages using enrichment with a cocktail of the top 7 STEC strains followed by purification via plaque assay. The isolated phages were subjected to host range tests and morphological observation by transmission electron microscopy. Ten samples (6 goat, 3 soil, and 1 cattle) contained various STEC-specific phages belonging to 3 families (Myoviridae, Siphoviridae, and Podoviridae). The phages isolated from 8 samples (5 goat, 2 soil, and 1 cattle) showed lytic activity against STEC O103, several of which exhibited a wide host range lytic against other top 7 STECs. Goat feces contained phages without isolation of STECs throughout the sampling periods. Two STECs, O174 and an O-antigen negative strain, were isolated from 1 soil and 1 cattle sample, respectively. This study indicates that STEC-specific phages were consistently isolated from goat feces. The prevalence of phages with wide and complimentary host range against the top 7 STECs, resulting in zero isolation of the bacterial pathogens, could be indicative of environmental biocontrol of phages in this niche.