Chlorhexidine Digluconate

Chlorhexidine digluconate (CHG) is bactericidal at 2–4% (5 min) except Enterococcus spp., S. epidermidis, MRSA and P. stuartii and yeasticidal at 2% (5 min). General mycobactericidal activity is not expected. Its antimicrobial activity is explained by cell adsorption resulting in precipitation of bacterial cytoplasm. Cellular defence mechanisms include resistance genes, cell membrane alterations, efflux pumps and plasmids. CHG reduces biofilm mass in developing and existing biofilms mostly poorly or moderately in several species. The effect of CHG on biofilm fixation is unknown. High MIC values indicating tolerance to CHG have been reported for isolates of B. subtilis, E. faecalis, K. pneumoniae and Proteus spp. (10,000 mg/l). Low-level exposure results in no MIC change in 53 species, a weak MIC change in 56 species and a strong MIC change in 43 species, which are stable in nine species, resulting in MIC values as high as 2048 mg/l (S. marcescens) and 1024 mg/l (P. aeruginosa). Low-level exposure can upregulate efflux pump genes, mostly increase biofilm formation and induce horizontal gene transfer (E. coli). Cross-tolerance to triclosan, benzalkonium chloride, hydrogen peroxide and selected antibiotics may occur. CHG-resistant isolates have been described in outbreaks and pseudo-outbreaks (A. xylosoxidans, B. cepacia, P. mirabilis, P. pickettii, MRSA, S. epidermidis, S. haemolyticus, S. marscescens) and with contaminated disinfectants (11 Gram-negative species). The overall probability of resistance to CHG of practical relevance is low to moderate in the absence of biofilm.