Isolation of bacteriophages against non-O157 and O157 Shiga toxin-producing Escherichia coli (STEC) from composting of non-fecal materials and the potential impact on produce safety

Authors: Liao, Yen-Te; QUINTELA, IRWIN - University Of Maine; Bridges, David; Wu, Vivian

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/9/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Composting is a complex process to produce fertilizers used to improve crop yields. A complete composting process usually confers bactericidal effect due to change of temperature and pH However, some produce outbreaks associated with Shiga toxin-producing E. coli (STEC) contamination were linked to inappropriate composting process. Studies have evaluated microbial community in manure-based composting because gastrointestinal tracts are the habitats of numerous foodborne pathogens, including STEC. Nevertheless, the similar information regarding non-fecal composting is lacking. Thus, the objectives of this study were to isolate bacterial STEC strains and the bacteriophages against the STEC from non-fecal composts, and to evaluate the bacteria-phages correlation and its potential impact on produce safety. Two liquid non-fecal composite samples were collected from a composting operation facility. For bacteriophage isolation, samples were enriched with a cocktail of 3 non-pathogenic E. coli and 14 STEC strains (2 strains each of O157 and top six non-O157), followed by isolation and purification using spot test assay and plaque assay. Plaque morphology and phage morphology were examined using stereomicroscope and transmitted electron microscopy, respectively. Presence of stx genes in the phages was determined using PCR. For isolation of O157 and non-O157 STEC strains, culture methods in combination with PCR-based confirmation were used. Results show that various phages against O45, O103, O111, O121, O145 and O157 were isolated, and only O103 phage were positive of stx1 gene. The phages (O45, O111 and O145) belong to Siphoviridae family were the most dominant, followed by Myoviridae (O121 and O157) and Podoviridae (O103). The plaque morphologies were different among the phages, with O103 phages produced the largest plaque size. In addition, some phages, such as O111 and O121, had wider host range. Neither O157 STEC nor top six non-O157 STEC strains were found in the composite samples. The finding of this study suggests that presence of STEC phages may contribute to zero isolation of STEC strains in addition to bactericidal effect from the composting process. However, further studies are necessary to understand the potential risk of the phages encoding stx genes may pose if those composite samples were used in produce farm.