Chlorhexidine (CHG) is a widely used, broad-spectrum antiseptic that reduces the presence of microbes on the skin and mucous membranes. Methicillin-resistant Staphylococcus aureus (MRSA) is a type of bacteria resistant to many common antibiotics, making it a significant challenge in healthcare settings. The use of chlorhexidine is a fundamental component of strategies aimed at controlling this drug-resistant organism.
How Chlorhexidine Targets Bacteria
Chlorhexidine is a cationic molecule, meaning it carries a positive electrical charge in solution. This positive charge is the basis of its destructive action against bacterial cells, which are surrounded by negatively charged cell walls and membranes. The antiseptic binds strongly to the bacterial surface, causing immediate destabilization and increasing the permeability of the cell’s outer layer, allowing CHG to penetrate further.
Once inside, the antiseptic disrupts the inner cytoplasmic membrane, which maintains the cell’s integrity and controls its internal environment. At lower concentrations, chlorhexidine acts as a bacteriostatic agent, causing the leakage of intracellular components like potassium ions and other metabolites. This loss compromises the cell’s ability to maintain homeostasis, slowing growth. At higher concentrations, typical of clinical formulations, the antiseptic acts as a bactericidal agent, causing the disruption of the cell membrane and rapid cell death.
Specific Uses Against MRSA Colonization
Chlorhexidine is a core component of infection control protocols designed to combat MRSA, particularly in healthcare environments. Its primary application is in decolonization strategies, which aim to reduce the amount of MRSA carried by patients and medical staff on their skin. This process prevents the bacteria from causing an active infection or spreading to other patients.
Daily bathing or washing with a chlorhexidine gluconate solution, typically 2% or 4%, is a common method for body decolonization. This topical application targets colonization sites on the skin, such as the groin, axilla, and skin folds, where MRSA often resides. This intervention has been shown to significantly reduce the risk of hospital-acquired infections, particularly in intensive care unit patients and those undergoing certain surgical procedures. The topical chlorhexidine wash contributes independently to reducing the bacterial load, though it is often used alongside a nasal antibiotic like mupirocin.
The Development of Reduced Susceptibility
While chlorhexidine is highly effective against most MRSA strains, there is concern regarding the development of reduced susceptibility, which is distinct from full antibiotic resistance. This phenomenon involves bacteria adapting to better tolerate the antiseptic’s effects over time, especially in environments with high CHG usage, like hospitals. Genetic changes in the MRSA genome, primarily the presence of qacA and qacB genes, are associated with this decreased sensitivity.
These qac genes encode for efflux pumps, which are specialized protein channels that actively pump the chlorhexidine molecule out of the bacterial cell before it reaches a lethal concentration. MRSA strains carrying these genes require a higher concentration of chlorhexidine to be killed compared to strains without them. The long-term use of daily CHG bathing protocols has been associated with an increase in the prevalence of these qacA/B genes in MRSA isolates recovered from patients. This reduced susceptibility may lead to decolonization failure and the potential spread of these more tolerant strains within clinical settings.
Safety Profile and Adverse Effects
Chlorhexidine is generally safe when used as directed, but it is associated with adverse effects ranging from mild irritation to severe allergic reactions. The most common side effect is irritant contact dermatitis, which manifests as dry, scaly, or rough skin at the application site. This irritation is uncomfortable but not dangerous, resulting from the chemical directly irritating the skin.
A more serious, though rare, concern is the risk of an immediate allergic reaction, including life-threatening anaphylaxis. Symptoms of this severe reaction, such as hives, swelling, or difficulty breathing, can occur rapidly following exposure. Healthcare professionals must be vigilant for these reactions, as they have been reported with all forms of chlorhexidine exposure, including topical washes and medical devices. Furthermore, chlorhexidine must be kept away from sensitive areas, such as the eyes, meninges, and middle ear, due to the risk of neurotoxicity and ototoxicity.