Staphylococcus epidermidis is one of the main colonizers of the human epithelium, resulting in a high probability of contamination of medical devices during insertion. Its ability to form biofilms makes infections persistent and difficult to treat. Chlorhexidine is a disinfectant widely used in healthcare settings to control and prevent healthcare-associated infections (HAIs). However, tolerance to this compound has been described and associated with efflux pump expression. This study aimed to evaluate the susceptibility of S. epidermidis to chlorhexidine digluconate (CHG) and investigate genetic determinants associated with tolerance. Seventy-two S. epidermidis isolates from bloodstream infections and neonatal nasal swabs were analyzed. Efflux pump activity was assessed using the Cartwheel method on ethidium bromide agar, and qacA/B and smr efflux pump genes were detected by PCR. Minimum bactericidal concentrations (MBCs) for CHG were determined in the presence and absence of organic matter with a 15-minute exposure. Biofilms were treated with different CHG concentrations for the same exposure time and evaluated by confocal microscopy. Active efflux systems were observed in 58% of isolates, and 85% (61/72) carried at least one efflux pump gene. The presence of qacA/B was associated with high efflux activity (p = 0.0001). CHG MBCs ranged from 1 (0.0001%) to 8 (0.0008%) mg/L without organic matter and from 4 (0.0004%) to 16 (0.0016%) mg/L with organic matter, with higher bacterial counts in the presence of organic matter. Confocal microscopy showed viable cells even at the highest CHG concentration tested (20,000 mg/L; 2%), especially in deeper biofilm layers, suggesting a predominantly superficial antiseptic effect. Despite S. epidermidis exhibiting active efflux systems and efflux pumps associated with chlorhexidine extrusion, the disinfectant demonstrated activity against the tested isolates. However, it was not effective against mature biofilms, highlighting the importance of this virulence factor in S. epidermidis and the relevance of this species as a challenge in the prevention of healthcare-associated infections (HAIs).
Souza et al. (Sun,) studied this question.