Physiological and genomic characterization of six virulent bacteriophages of Shiga toxin-producing Escherichia coli O157:H7 for biocontrol and detection applications

  • Author / Creator
    Beatriz Iara Cabral e Pacheco
  • Despite multiple control strategies in all steps of the food production chain, outbreaks of foodborne pathogens are common worldwide. More effective ways to prevent, eliminate or at least detect their presence before products reach consumers are of great interest to the general public, the food industry, and public health agencies. A promising approach is the use of bacteriophages (phages), viruses that specifically infect bacteria, in the biocontrol and detection of these pathogens. Escherichia coli O157:H7 is an important bacterial pathogen commonly associated with the contamination of vegetables, meat and other animal products. Healthy cattle are the primary reservoir of E. coli O157:H7 and consequently of its predators, phages. In the present work, six E. coli O157:H7 phages previously isolated from commercial feedlots in Southern Alberta were characterized in terms of morphology, host range and lytic capability, adsorption kinetics, and virulence dynamics. The six phages belong to the Siphoviridae family. The screening of 30 different E. coli O157:H7 strains against all phages revealed that at least 22 were susceptible to all six phages, with 14 being extremely sensitive. Adsorption kinetics results combined with two different reaction models (single-step and sequential adsorption) indicated adsorption occurred in two steps: an initial reversible binding followed by an irreversible one. Moreover, the phage genomes were sequenced and analyzed. The six phages shared high genomic similarity between themselves and with other viruses isolated from the same trial but at different geographical locations and collected at different sampling times. We thus hypothesize these phages represent different variants of the dominant E. coli O157:H7 phage in their ecological niche. Furthermore, although the genomes of five of the six phages shared 99.9% pairwise similarity, their host range and lytic capability, adsorption kinetics, and infection dynamics differed. Twelve nonsynonymous point mutations differentiated the genetic codes of these phages and, notably, six of these mutations were located in genes encoding putative tail fibers, responsible for host recognition and binding. Thus, these point mutations are likely causes of differences in the phage phenotypes observed, and would be represent interesting locations for phage genetic engineering to tailor host specificity. The present work sets a framework for the identification and selection of phages with potential for biocontrol and/or detection of E. coli O157:H7, provides valuable insights on phage host relationship mechanisms, and suggests genetic basis for traits of interest.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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