Adaptive microbial response to low-level benzalkonium chloride exposure.

Benzalkonium chloride (BAC) is a widely used biocidal agent in health care, mainly in surface disinfectants and disinfectant cleaners. The aim of this review was to evaluate the potential of bacteria to adapt to low-level BAC exposure. A maximum four-fold increase in minimum inhibitory concentration (MIC) was found in most of the 57 bacterial species evaluated. A strong adaptive, mostly stable, change in MIC was described in strains or isolates of Pantoea spp., Enterobacter spp., Staphylococcus saprophyticus and Escherichia coli (up to 500-fold, 300-fold, 200-fold and 100-fold, respectively). The highest MIC values after adaptation were 3000 mg/L (Salmonella typhimurium), 2500 mg/L (Pseudomonas aeruginosa), 1500 mg/L (Enterobacter spp.) and 1000 mg/L (E. coli and S. saprophyticus). Cross-resistance to selected antibiotics (e.g. ampicillin, cefotaxime and ceftazidime) and biocidal agents (e.g. didecyldimethylammonium bromide, didecyldimethylammonium chloride, triclosan and chlorhexidine) was found in some isolates. A significant upregulation of transporter and efflux pump genes was found in Burkholderia cepacia complex and E. coli. It is probable that adapted isolates are not killed by BAC-based disinfectants at the recommended concentration. The use of BAC in patient care and all other settings, such as consumer products and households, should be critically assessed and restricted to indications with a proven health benefit or justifiable public health benefits. Other biocidal agents with a lower or no selection pressure should be preferred if the efficacy, acceptance and skin or material compatibility are at least as good for the intended use.