Comparison of ciprofloxacin and aminoglycoside susceptibility testing for ceftriaxone non-susceptible Enterobacterales by disk diffusion and VITEK 2 vs. broth microdilution using updated Clinical and Laboratory Standards Institute breakpoints
Bibliographic record
Abstract
BACKGROUND: Fluoroquinolones and aminoglycosides are potential treatment choices in the setting of increasingly multi-drug resistant Enterobacterales. The Clinical & Laboratory Standards Institute (CLSI) breakpoints for fluoroquinolones and aminoglycosides in the Enterobacterales were revised in 2019 and 2022, respectively. However, performance of existing widely used automated systems, such as the VITEK 2 AST-N391 card, has not been extensively tested for MDR isolates at these new breakpoints. OBJECTIVE: To assess performance of the new breakpoints for ciprofloxacin, gentamicin, and tobramycin on the VITEK 2 system (bioMérieux, France) and disk diffusion by comparing to broth microdilution for ceftriaxone nonsusceptible Enterobacterales. METHODS: Ninety-four ceftriaxone non-susceptible Escherichia coli and Klebsiella pneumoniae isolates were identified between January 2021-June 2023. Broth microdilution was used as the reference standard against which disk diffusion and VITEK 2 susceptibility testing were compared. For the Vitek 2, we used the AST-N391 card and interpreted the results according to the updated CLSI breakpoints. RESULTS: Overall, 22.3% of isolates were susceptible to ciprofloxacin by BMD. Compared to BMD, disk diffusion had an overall minor error rate of 7.4% (95%CI 3.0-14.7%) with 0 major or very major errors (97.5% CI 0-3.8%). For the VITEK 2, a minor error rate of 13.8% (95% CI 7.6-22.5%), major error rate 19.0% (95%CI 7.7-40.0%) and very major error rate 0% (97.5%CI 0-3.8%) was noted. By comparison, 69.1% and 56.4% of isolates were susceptible to gentamicin and tobramycin, respectively. Disk diffusion and the VITEK 2 system both correctly categorized 100% of gentamicin susceptible and non-susceptible isolates. For tobramycin, disk diffusion had a 3.2% rate of misclassification (all minor errors) and the VITEK 2 had 2.1% rate of misclassification (all minor errors). There were no major or very major errors. CONCLUSIONS: Our findings suggest that both disk diffusion and to a greater extent the AST-N391 card for the VITEK 2 system will overcall non-susceptibility according to current CLSI breakpoints for ciprofloxacin. By contrast, the existing AST-N391 VITEK 2 card can likely be used to correctly infer susceptibility to gentamicin and tobramycin.
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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 | 0.007 | 0.022 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".