Characterization of Shiga toxin-producing Escherichia coli bacteriophages isolated from agricultural environments and examination of their prevalence with bacterial hosts

Abstract

In the natural environment, ruminant livestock, including cattle, are the main reservoir of the outbreak–causing strains of Shiga toxin-producing Escherichia coli (STEC), where bacteriophages sustainably thrive as well. This study focuses on the characterization of STEC-specific bacteriophages isolated from cow manure samples in Maine farms and examines their prevalence with STEC hosts. Phenotypic features of representative isolates were characterized by using a transmission electron microscope. Similarly, host range, one-step growth curve, thermal stability, lytic capability, and genomic analyses were performed to fully characterize selected representative isolates. Results showed that representative bacteriophage isolates belong to Myoviridae (S6P10 and S14P12) and Siphoviridae (S19). The most prevalent and common bacteriophages (46%) were specific to the O26 serogroup. The farm C sampling site had highly heterogenous bacteriophage populations that were specific to six STEC serogroups. The most prevalent bacteriophage isolate (S1P5, Escherichia phage vB_EcoM-S1P5QW) was verified to have a double-stranded DNA genome (166,102 bp) with 266 CDs of which 130 have known functions. The majority of the diverse bacteriophage isolates had strong lytic capabilities and a narrow host range that could withstand selected temperature conditions (−20, 37, and 62°C). Results of bacterial screening showed that STEC host strains were not detected in Farms A, C, and E, but were detected on Farms B and D. In conclusion, the highly-diverse bacteriophage ecology found in cow manure samples may have been an important element in shaping the population of STEC serogroups, specifically in its natural environment, which can provide useful tools for potential antibiotic-free therapeutics and diagnostic technologies.