Characterization of Two New Shiga Toxin-Producing Escherichia coli O103-Infecting Phages Isolated from an Organic Farm.

Yujie Zhang,Valerie M Lavenburg,Alexandra Salvador,Vivian C H Wu,Yen-Te Liao

doi:10.3390/microorganisms9071527

Abstract

Shiga toxin-producing Escherichia 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. This study was to biologically and genomically characterize two STEC O103-infecting bacteriophages, vB_EcoP-Ro103C3lw (or Ro103C3lw) and vB_EcoM-Pr103Blw (or Pr103Blw), isolated from an organic farm. Based on genomic and morphological analyses, phages Ro103C3lw and Pr103Blw belonged to Autographiviridae and Myoviridae families, respectively. Ro103C3lw contained a 39,389-bp double-stranded DNA and encoded a unique tail fiber with depolymerase activity, resulting in huge plaques. Pr103Blw had an 88,421-bp double-stranded DNA with 26 predicted tRNAs associated with the enhancement of the phage fitness. Within each phage genome, no virulence, antibiotic-resistant, and lysogenic genes were detected. Additionally, Ro103C3lw had a short latent period (2 min) and a narrow host range, infecting only STEC O103 strains. By contrast, Pr103Blw had a large burst size (152 PFU/CFU) and a broad host range against STEC 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 these two phages’ genomic features with the potential antimicrobial activities against STEC O103.

Highlights

Bacteriophages are viruses that infect bacteria and are the most abundant biological entities in the biosphere, with estimated numbers of 1031 virions [1]
Two newly isolated phages—Ro103C3lw and Pr103Blw—were characIn this work, two newly isolated phages—Ro103C3lw and Pr103Blw—were characterterized to evaluate the biologic and genomic features associated with antimicrobial activized to evaluate the biologic and genomic features associated with antimicrobial activities, ities, indicating their biocontrol potential against Shiga toxin-producing Escherichia coli (STEC) O103 strains
Short replication time is one of the primary strategies for phage to respond to external Short replication time is one of the primary strategies for phage to respond to external pressures, such as high bacterial densities (108 CFU/mL)

Summary

Introduction

Bacteriophages (or phages) are viruses that infect bacteria and are the most abundant biological entities in the biosphere, with estimated numbers of 1031 virions [1]. Phages are widely present in different environments, such as the global ocean, lake, and agricultural soil, and can infect their bacterial hosts as natural predators [2,3]. Bacteriophages are classified into lytic phages and lysogenic phages [4]. The emergence of antibiotic-resistant pathogenic bacteria has become a crucial health problem worldwide. Lytic phages have been considered as potential antimicrobial agents to reduce antibiotic-resistant issues [8,9]. Phage-based biocontrol of bacterial pathogens has been applied in several areas, including food processing, agriculture, and aquaculture [10,11,12]. Phages should have several biological and genetic features to be considered suitable biocontrol candidates, such as a broad host range and free of Microorganisms 2021, 9, 1527.

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