Characterization of two new Shiga toxin-producing Escherichia coli O103-infecting phages isolated from an organic farm

Authors: ZHANG, YUJIE - Oak Ridge Institute For Science And Education (ORISE); Liao, Yen-Te; Salvador, Alexandra; LAVENBURG, M. - Volunteer; Wu, Vivian

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2021
Publication Date: 7/17/2021
Citation: Zhang, Y., Liao, Y., Salvador, A., Lavenburg, M.V., Wu, V.C. 2021. Characterization of two new Shiga toxin-producing Escherichia coli O103-infecting phages isolated from an organic farm. Microorganisms. 9(7):1527. https://doi.org/10.3390/microorganisms9071527.
DOI: https://doi.org/10.3390/microorganisms9071527

Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) is one of the major foodborne pathogens that can cause severe human illness, such as bloody diarrhea and kidney failure. In recent years, due to the overuse of antibiotics, the emergence of antibiotic-resistant strains has become a crucial health problem worldwide. Lytic phages, which could directly infect and lyse bacterial hosts, are considered as alternative and promising antimicrobial agents to prevent the spread of foodborne pathogens. There are increasing numbers of lytic bacteriophages against STEC pathogens isolated from the diverse environment; however, the phages that specifically target STEC O103 are less explored and characterized. Therefore, in this study, two lytic bacteriophages—Ro103C3lw and Pr103Blw—with different morphologies were isolated for biological and genomic characterization. The results showed that phage Ro103C3lw had a short and non-contractile tail and only infected STEC O103 strains. In contrast, phage Pr103Blw had a long and contractile tail and infected different STEC strains and one Salmonella strain. Additionally, both phages showed strong antimicrobial activities to inhibit the growth of STEC O103:H2 strains. Although these two phages had different genomic features, no unwanted genes, such as virulence or antibiotic resistance genes, were found in both phages. This study's findings demonstrate that phage Ro103C3lw and Pr103Blw have the potential as antimicrobial agents for STEC O103 pathogens.

Technical Abstract: Shiga toxin-producing E. coli (STEC) O103 strains have been recently attributed to various foodborne outbreaks in the United States. Due to the emergence of antibiotic-resistant strains, lytic phages are considered as alternative biocontrol agents. However, little information is available regarding characterization of the phages specific to STEC O103 strains. Thus, the objective of this study was to biologically and genomically characterize two STEC O103-infecting bacteriophages, vB_EcoP-Ro103C3lw and vB_EcoM-Pr103Blw, isolated from non-fecal compost and cattle feces. Based on genomic and morphological analyses, phages Ro103C3lw and Pr103Blw belonged to Podoviridae and Myoviridae families, respectively. Ro103C3lw contained a 39,389-bp double-stranded DNA and encoded a unique tail fiber with depolymerases activity, resulting in a huge halo around each plaque. Pr103Blw had an 88,421-bp double-stranded DNA with 26 predicted tRNAs associated with enhancement of the phage fitness. Within each phage genome, no virulence, antibiotic-resistance, and lysogenic genes were detected. For biological properties, Ro103C3lw had a short latent period of 6 min and a narrow host range, infecting only STEC O103 strains. In contrast, Pr103Blw had a large burst size of 130 PFU/CFU and a broad host range against different STEC serotypes (O103, O26, O111, O157:H7) and Salmonella Javiana strains. Furthermore, both phages showed strong antimicrobial activities against STEC O103:H2 strains. The findings provide valuable insight into the biological and genomic features of these two phages with the potential antimicrobial activities against STEC O103 pathogens.