A Novel, Widespread qacA Allele Results in Reduced Chlorhexidine Susceptibility in Staphylococcus epidermidis

Abstract

Chlorhexidine gluconate (CHG) is a topical antiseptic widely used in health care 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 that 63 (6%) of these isolates had elevated CHG MICs (≥4 μg/ml). Screening of all 1,050 isolates for the qacA/B gene (the same qac gene with A or B allele) by restriction fragment length polymorphism (RFLP) yielded 56 isolates with a novel qacA/B RFLP pattern, qacA/B273. The CHG MIC was significantly higher for qacA/B273-positive isolates (MIC50, 4 μg/ml; MIC range, 0.5 to 4 μg/ml) than for other qac groups: qacA-positive isolates (n = 559; MIC50, 1 μg/ml; MIC range, 0.5 to 4 μg/ml), qacB-positive isolates (n = 17; MIC50, 1 μg/ml; MIC range, 0.25 to 2 μg/ml), and qacA/B-negative isolates (n = 418, MIC50, 1 μg/ml; MIC range, 0.125 to 2 μg/ml) (P = 0.001). A high proportion of the qacA/B273-positive isolates also displayed methicillin resistance (96.4%) compared to the other qac groups (24.9 to 61.7%) (P = 0.001). Whole-genome sequencing revealed that qacA/B273-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 Staphylococcus epidermidis sequence type 2 clone. By searching available sequence data sets, we identified 39 additional qacA4-carrying S. epidermidis strains from 5 countries. Curing an isolate of qacA4 resulted in a 4-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.

Comparative genomics of Staphylococcus epidermidis from prosthetic-joint infections and nares highlights genetic traits associated with antimicrobial resistance, not virulence

“…Gene presence was determined based on a >80 % hit length and >90 % sequence identity. We further investigated point mutations associated with rifampicin [9, 47, 48], fusidic acid [49], co-trimoxazole [50], linezolid [9], daptomycin [51, 52] and quinolone resistance [53–55], as well as increased tolerance towards chlorhexidine [56], see Table S4 for positions included in analyses. In addition, the reference sequence CP022250, positions 4218–2674, was used to query the assembled genomes for presence of qacA/B .…”

Inactivation of genes in oxidative respiration and iron acquisition pathways in pediatric clinical isolates of Small colony variant Enterobacteriaceae

“…Whole genome sequencing and assembly of the resulting sequencing reads for the NCV and SCV co-isolates were performed as previously described 25 , 26 . Briefly, DNA was extracted from using the MoBio UltraClean Microbial DNA Isolation kit.…”

Chlorhexidine gluconate bathing in children with cancer or those undergoing hematopoietic stem cell transplantation: A double‐blinded randomized controlled trial from the Children's Oncology Group

“…We chose ≥4 a priori because this was a cut point used in other studies 25,26 . In another study of these staphylococci isolates, we found that the presence of a CHG MIC ≥4 was associated with a newly described variant of the qacA gene, which has the capacity to efflux CHG 7 . This new variant also was found to be associated with resistance to commonly used antimicrobials.…”

“…Skin swabs of the neck and axilla were collected at baseline, at day 45 (±7 days), and at day 90 (±7 days) to assess the MIC in skin staphylococcal isolates (see Supporting Information for additional detail). CHG MIC was determined as previously described 7 …”