Evaluation of Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry for Microbiological Typing in a Serratia marcescens Outbreak
Bibliographic record
Abstract
Background. There is limited experience using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry for the typing of isolates in outbreak investigations. The performance of MALDI-TOF typing was evaluated against 2 different reference methods in the context of a neonatal intensive care unit (NICU) outbreak of invasive Serratia marcescens. Methods. Outbreak-related patient and environmental isolates and frozen isolates of S marcescens within the past 10 years were subcultured and subjected to full protein extraction. Each extracted isolate was applied to 8 target spots and run in triplicate on the MALDI-TOF. A master spectrum was compiled for each isolate using MALDI Biotyper 3 software. A dendrogram was created using this collection of master spectra and compared with results obtained from 2 traditional typing methods, pulse-field gel electrophoresis (PFGE) and random amplification of polymorphic DNA (RAPD). Results. Overall, 19 invasive and noninvasive samples from 14 patients and 11 environmental samples were included. Four blood cultures from 3 different patients were found to harbor identical S marcescens strains using PFGE and RAPD typing methods. These isolates appeared as a cluster on the MALDI-TOF dendrogram, with no distance between 3 of them and minimal distance separating the fourth one from the triad. The environmental isolates were demonstrated to be unrelated to all patient isolates using PFGE. Likewise, the MALDI-TOF dendrogram displayed 2 major clades, which predominantly separated the patient and environmental isolates. Conclusion. In a small invasive S marcescens NICU outbreak, typing by MALDI-TOF performed well compared with traditional methods. A particular attraction of this method is that it is increasingly available at clinical laboratories and can provide rapid results to inform infection control measures in real time. Further characterization of the strain discriminatory ability of the MALDI-TOF could expand its utility as a rapid way of typing in an outbreak setting as an adjunct to slower and less readily accessible typing methods. Disclosures. All authors: No reported disclosures.
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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 | 0.003 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 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".