A novel <i>qacA</i> allele results in an elevated chlorhexidine glu conate minimum inhibitory concentration in cutaneous <i>Staphylococcus epidermidis</i> isolates
Bibliographic record
Abstract
Abstract Chlorhexidine gluconate (CHG) is a topical antiseptic widely used in healthcare settings. In Staphylococcus spp., the pump QacA effluxes CHG, while the closely related QacB cannot due to a single amino acid substitution. We characterized 1,050 cutaneous Staphylococcus isolates obtained from 173 pediatric oncology patients enrolled in a multicenter CHG bathing trial. CHG susceptibility testing revealed 63 (6%) of these isolates had elevated CHG MICs (≥ 4 μg/mL). Screening of all 1,050 isolates for qacA/B by restriction fragment length polymorphism (RFLP) yielded 56 isolates with a novel qacA/B RFLP pattern, qacAB 273 . The CHG MIC was significantly higher for qacAB 273 -positive isolates (MIC 50 : 4 μg/mL, [range: 0.5 – 4 μg/mL]) compared to other qac groups: qacA -positive (n=559, 1 μg/mL, [0.5 – 4 μg/mL]), qacB -positive (n=17, 1 μg/mL, [0.25 – 2 μg/mL]), and qacA/B- negative (n=418, 1 μg/mL, [0.125 – 2 μg/mL], p=0.001). The qacAB 273 -positive isolates also displayed a high proportion of methicillin resistance (96.4%) compared to other qac groups (24.9 – 61.7%, p=0.001). Whole genome sequencing revealed that qacAB 273 -positive isolates encoded a variant of QacA with 2 amino acid substitutions. This new allele, named qacA4 , was carried on the novel plasmid pAQZ1. The qacA4 -carrying isolates belonged to the highly resistant S. epidermidis clone ST2 and were collected from multiple centers across the United States and Canada. Curing an isolate of qacA4 resulted in a four-fold decrease in the CHG MIC, confirming the role of qacA4 in the elevated CHG MIC. Our results highlight the importance of further studying qacA4 and its functional role in clinical staphylococci. Importance Staphylococcus epidermidis is an important cause of infections in patients with implanted devices. Bathing with chlorhexidine gluconate (CHG), a topical antiseptic, has been shown to reduce rates of device-associated infections, especially those caused by S. epidermidis . In S. epidermidis , reduced susceptibility to CHG is associated with carriage of the qacA gene. As part of a multicenter CHG bathing trial, we obtained cutaneous Staphylococcus isolates from pediatric oncology patients across the United States and Canada. We identified a group of isolates capable of surviving in higher concentrations of CHG and determined a novel allele of qacA , termed qacA4 and carried on the novel plasmid pAQZ1, was responsible for the isolates’ survival in higher CHG concentrations. The qacA4 -carrying S. epidermidis isolates belonged to the highly resistant and virulent ST2 clonal type. Our results highlight the need to understand the global distribution of novel qacA alleles, including qacA4 , and their mechanistic effect on efflux.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".