Cationic antiseptics: diversity of action under a common epithet

Cationic antimicrobials have been in general use within clinical and domestic settings for over half a century. Recently, the use of antiseptics and disinfectants has been questioned in such settings because of the possibility that chronic exposure of the environment to such agents might select for less susceptible strains towards these agents and towards third party antibiotics. Whilst no supportive evidence has emerged from retrospective field studies of high use environments such debate has tempered new applications for these molecules. In the clinic, use of antiseptics, together with products, such as dressings, catheters and sutures, which are impregnated with biocides has increased. Prominent amongst these biocides are the cationics. Much of the research pertaining to the mechanisms of action of cationic antibacterials was conducted in the 1960s and 1970s and has not been subject to extensive review. Analysis of available publications suggest that monoquaternary ammonium compounds (QAC, cetrimide, benzalkonium chloride), biquaternaries and bisbiguanides (Chlorhexidine, Barquat), and polymeric biguanides (Vantocil, Cosmocil) whilst having similarities in action mechanism, differ substantially in the nature of their interaction with cell envelopes. This has profound implications in terms of cross-resistance where changes in susceptibility towards QAC is not reflected in changes towards other cationics. This review examines action mechanisms for these agents and highlights key differences that render them distinct categories of antibacterial agent. © 2005 The Society for Applied Microbiology.