Physiological and genomic characterization of six virulent bacteriophages of Shiga toxin-producing Escherichia coli O157:H7 for biocontrol and detection applications
Bibliographic record
Abstract
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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".