Chlorhexidine Tolerance Genes and Nosocomial Infections

Chlorhexidine Tolerance Genes and Nosocomial Infections

A recent study evaluating nosocomial Staphylococcus aureus isolates for the presence of genes associated with chlorhexidine tolerance found that 45% of isolates carried one or more genes, and that strains carrying these tolerance genes were associated with reduced susceptibility to systemic antimicrobial agents and increased rates of bloodstream infections.

Chlorhexidine Tolerance Genes and Nosocomial Infections

Chlorhexidine Tolerance Genes and Nosocomial Infections

S aureus healthcare-associated infections (HAIs) continue to place a financial strain on healthcare systems and lead to significant morbidity and mortality in adults and children. Use of chlorhexidine topical decontamination has increased as a result of evidence supporting its role in reducing the spread of multidrug-resistant organisms and preventing such HAIs as central line–associated bloodstream infections (CLABSIs). Concerns have arisen over declining susceptibility to chlorhexidine and potential unintended clinical consequences.

Isolates underwent polymerase chain reaction (PCR)-based testing for detection of the smr and qacA/Bgenes—genes encoding multidrug efflux pumps associated with elevated minimum bacterial concentrations (MBCs) for chlorhexidine. Susceptibility testing for systemic antimicrobial agents was also performed. In total, 247 cases were identified, with most (56.3%) occurring in the neonatal intensive care unit.

Overall, 111 of 247 isolates (45%) had one or both genes associated with chlorhexidine tolerance; 33.1% were positive for smr, 22.7% were positive for qacA/B, and 10.9% were positive for both. The presence of tolerance genes was higher among methicillin-resistant S aureus (MRSA) isolates. Comparing isolates with and without chlorhexidine tolerance genes, smr-positive S aureus isolates were more likely to be resistant to methicillin, clindamycin, and/or ciprofloxacin. Isolates with the qacA/B gene were associated with the presence of a central venous catheter and vancomycin minimum inhibitory concentrations (MICs) > 2 µg/mL. Presence of either gene was associated with a diagnosis of bacteremia. The presence of both genes seemed to have a synergistic effect, leading to high MICs and MBCs to chlorhexidine. Tolerance genes seemed to have no impact on duration of hospitalization and in-hospital mortality.

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