Recently introduced qacA/B genes in Staphylococcus epidermidis do not increase chlorhexidine MIC/MBC

Area of Science:

• Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Chlorhexidine is a common disinfectant used to prevent surgical site infections.
• Concerns exist regarding chlorhexidine selecting for resistant bacterial strains, potentially linked to qacA/B efflux pumps.
• Methicillin-resistant Staphylococcus aureus (MRSA) tolerance to chlorhexidine has been previously reported.

Purpose of the Study:

• To investigate if high-level chlorhexidine exposure selects for tolerant colonizing Staphylococcus epidermidis.
• To assess the consequences of long-term chlorhexidine exposure on S. epidermidis.
• To determine the prevalence of qacA/B genes in S. epidermidis isolates.

Main Methods:

• Susceptibility testing (MICs/MBCs) and qacA/B gene carriage analysis of S. epidermidis.
• Comparison of isolates from healthcare workers with high chlorhexidine exposure versus non-users.
• Analysis of historical S. epidermidis blood isolates (pre-1960s) against contemporary isolates.

Main Results:

• No correlation found between chlorhexidine hand rub use and increased S. epidermidis tolerance or qacA/B gene presence in healthcare workers.
• 55% of current S. epidermidis blood isolates carried qacA/B genes.
• Historical S. epidermidis isolates lacked qacA/B genes, yet showed comparable chlorhexidine susceptibility to current isolates.

Conclusions:

• Chlorhexidine as a hand rub does not appear to select for S. epidermidis with increased chlorhexidine minimum inhibitory concentrations (MICs) or minimum bactericidal concentrations (MBCs).
• The absence of qacA/B genes in historical isolates suggests long-term exposure to biocides may drive their selection.
• Further research is needed to understand the long-term implications of biocide use on bacterial resistance mechanisms.