Chlorhexidine, first described in 1954, is now the standard of care topical broad-spectrum biocide in the prevention of healthcare-associated infections, with bacteriostatic properties at low concentrations, and bactericidal properties at higher concentrations. It exhibits activity against gram-positive bacteria, gram-negative bacteria, some enveloped viruses, and fungi, and demonstrates longer-lasting residual effects than other antiseptic agents, such as triclosan.^1,2  CHG is responsible for the antimicrobial effect of ReliaTect® post-operative dressing.³

Positively-charged CHG binds to negatively-charged bacterial cell membranes and walls; at low concentrations, this association interrupts cellular osmoregulatory and metabolic capacity, inhibiting cellular respiration. At higher concentrations, CHG destroys bacterial membrane integrity completely, leading to leakage of cellular contents, cell lysis, and death.¹

There are no standardized methods for chlorhexidine susceptibility testing—or indeed a consensus definition of CHG “resistance”—which frustrates a clear determination of whether, and to what extent, prolonged use of CHG fosters the development of resistant bacteria.^1,4  However, analysis of the potential mechanisms of bacterial resistance, combined with real-world data of CHG use, suggests that concerns about reduced microbial susceptibility to CHG may be overstated.¹

Plasmid-mediated multidrug efflux pumps, encoded by qacA and qacB genes, are the most widely reported mechanism of bacterial resistance to CHG: the QacA pump system, found in gram- positive bacteria such as resistant staphylococci, transports chlorhexidine outside the bacterial cell.^1,5,6  Expression of qacA is under the regulatory control of the QacR protein, which inhibits qacA transcription; however, when a substrate such as chlorhexidine binds to QacR, the repressor is removed, and the qacA pump gene expressed.^1,6

Gene-prevalence studies that do not assess susceptibility rates may therefore overestimate the rates of CHG-tolerance.¹  There is also little evidence suggesting that plasmid-mediated antibiotic resistance common among gram-negative bacteria is associated with CHG-resistance.¹⁰

ReliaTect is a sterile post-operative dressing consisting of a polyurethane film, coated with a transparent chlorhexidine gluconate acrylic adhesive. CHG distinguishes ReliaTect from other transparent post-op dressings; a recent study found it significantly outperformed both placebo and gauze dressings in reducing MRSA contaminating a surgical wound in a porcine, incisional-wound model.³ By contrast, the current available evidence indicates that dressings containing silver are not associated with a lower incidence of surgical site infections (SSIs) than silver-free dressings.¹¹