Investigation of Fluoroquinolone resistance-associated mutations in Canadian clinical isolates and laboratory mutants of Streptococcus pneumoniae
Bibliographic record
Abstract
The purpose of this thesis was to evaluate how S. pneumoniae isolates are genetically altered as fluoroquinolone resistance increases in Canada.In order to address this question, it is essential that the fluoroquinolones be fully characterized for activity, resistance development, and mechanisms to prevent the selection of resistant isolates.This study was comprised of 3 objectives.Firstly, to molecularly characterize ciprofloxacin-resistant isolates collected over 7 years for resistance-associated substitutions, efflux, serotype, and molecular subtyping using pulsed-field gel electrophoresis.Secondly, to ascertain if the prevalence of fluoroquinolone resistanceassociated substitutions has increased in fluoroquinolone-susceptible isolates.Lastly, the mutant prevention concentration (MPC) was evaluated for its potential to restrict the selection of fl uoroquinolone-resistant isolates during antibiotic therapy.S. pneumoniae isolates were collected as part of the Canadian Respiratory Organism Susceptibility Study between 1997198 and 2004.Fluoroquinolone resistance was found to primarily result from the spontaneous development of resistance substitutions, not clonal expansion.An increase was observed in the number of isolates with substitutions in both target enzymes in conjunction with a decrease in the number of effl ux-positive isolates.The percent of fluoroquinolone-susceptible isolates with fluoroquinolone resistance-associated substitutions increased in Canada between 1997 and 2003.Using this dafa, microbiological breakpoints were determined to separate wild-type ^S.pneumoniae isolates from those considered susceptible by standard susceptibility criteria but possessing resistance-associated substitutions.Microbiological breakpoints permit a means to conduct surveillance of genetic alterations resulting in fluoroquinoloneresistance.The MPC has been proposed as a dosing strategy that may limit the selection of resistance during antimicrobial therapy.It was demonstrated throughout this study that the MPCs vary widely based on the original genetic makeup of the S. pneumoniae isolate.Fluoroquinolone resistance has increased in Canada throughout the course of this study and the ciprofloxacin-resistant isolates were found to be genetically evolving.The resistance increase does not appear to be attributable to a pooling of resistance substitutions in fluoroquinolone-susceptible isolates.MPC dosing may be effective at limiting the selection of fluoroquinolone resistance from a wild-type population, but will be unable to remedy the difficulties recently highlighted with S. pneumoniae isolates carrying first-step substitutions.DNA Isolation vl b.AmplifTcation of the Quinolone Resistance-Determining Regions of gyrA and parC c. d. e. f. at a. b. 7. Serofyping 8. Single-step a. b. c.AmplifÏcation of gyrA, pørC,, and pørE Agarose Gel Electrophoresis Purification and Quantitation of DNA Template Sequencing Reaction Purification of Sequencing Products by EthanoVSodium Acetate 42 42 43 for Sequencing 44 44 Precipitation
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".