The effects of environmental factors on the prevalence and diversity of bacteriophages lytic against top six non-O157 Shiga toxin-producing Escherichia coli on an organic farm

Authors: Liao, Yen-Te; LAVENBURG, VALERIE - Volunteer; Lennon, Marion; Salvador, Alexandra; Hsu, Angeline; Wu, Vivian

Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2020
Publication Date: 10/19/2020
Citation: Liao, Y., Lavenburg, V., Lennon, M., Salvador, A., Hsu, A.L., Wu, V.C.H. 2020. The effects of environmental factors on the prevalence and diversity of bacteriophages lytic against top 6 non-O157 Shiga toxin-producing Escherichia coli on an organic farm. Journal of Food Safety. https://doi.org/10.1111/jfs.12865.
DOI: https://doi.org/10.1111/jfs.12865

Interpretive Summary: Lytic bacteriophages that can infect their bacterial hosts are ubiquitous in the environment. The majority of the phages lytic against pathogenic E. coli strains are isolated from the fecal-contaminated environment due to the natural reservoir of their E. coli bacterial hosts. This study focused on the prevalence of the phages lytic against the top 6 well-known pathogenic E. coli strains— Shiga toxin-producing E. coli (STEC)—from different environmental samples collected from an organic farm containing animal-active and produce-growing areas. The results of this study showed various bacteriophages lytic against 6 different groups of non-O157 STEC strains, including O26, O45, O103, O111, O121, and O145, were isolated from water, soil, sediment, and animal feces, and the majority of phage-positive samples were collected from the animal-active area. The results also showed that the phages that infected STEC O103 were the most prevalent phages, which were likely spread through rain precipitation from fecal samples to the surrounding area. Additionally, the sample that was positive E. coli O103:H2 strain did not have any phages isolated. The findings of this study indicate animals, such as goats and cattle, are the primary contributing factor to the prevalence of the phages lytic against STEC in the organic farm. Additionally, the presence of the phages reduce the prevalence of their STEC bacterial hosts in the surrounding environments.

Technical Abstract: Bacteriophages (or phages) specific to Shiga toxin-producing E. coli (STEC) strains are frequently isolated from the animal-associated environments primarily because ruminant animals are the natural reservoir of STEC. However, little is known about these phages in produce-growing environments. The objective of this study was to determine the effects of environmental factors on the prevalence of the phages lytic against O157 and the top 6 non-O157 STEC in an organic farm. A total of 370 samples were collected from an organic farm, containing animal-active and produce-growing areas for one year. A bacterial cocktail, including non-pathogenic and pathogenic E. coli strains, was used for phage isolation. Meanwhile, culture methods and PCR were used to isolate STEC strains. Weather information was also collected for each sampling trip. Twenty-eight samples contained the phages lytic against STEC, of which 26 were collected from the animal-active area. Moreover, the winter season tended to have a higher phage prevalence than other seasons likely due to high rain precipitation. The phages belonging to the Myoviridae family and those lytic against STEC O103 were the most prevalent. One E. coli O103:H2 was isolated from a water sample where no phages lytic against STEC O103 was found. The findings indicate that animal is the primary factor contributing to the prevalence of the phages lytic against STEC in the surrounding environment of the organic farm, and the presence of these phages likely contribute to the negative correlation with their STEC hosts.