Determination of the antibacterial efficacy of several antiseptics tested on skin by an 'ex-vivo' test

There are many skin antiseptics commercially available. Although their anti bacterial activity has often been well studied [1], their potential effecti veness on skin remains poorly documented. To date, in-vivo protocols design ed for the testing of the antimicrobial efficacy of antiseptics cannot use, for ethical reasons, pathogenic bacteria or new formulations whose toxicit y in human subjects is unknown. An 'ex-vivo' test was recently developed to overcome these problems. Freshly excised human skin from abdominal or brea st reduction was placed in a diffusion cell containing a maintenance medium in the recipient compartment. A bacterial inoculum was then applied to the stratum corneum and, after a drying step, antiseptic formulations were eva luated for their antimicrobial activity. Several micro-organisms were inves tigated: - Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), E nterococcus faecalis, vancomycin-resistant Ent, faecium (VRE), S. epidermid is, Pseudomonas aeruginosa and Escherichia coli - with several biocides - p ara-chloro-meta-xylenol (PCMX, active compound of Dettol), povidone iodine, triclosan tin isopropanol) and chlorhexidine. Results from the ex-vivo tes t were compared with results obtained in suspension and glass-carrier tests . The bactericidal activity of the biocides depended upon the test performe d and results were generally significantly different from one method to the other. All biocides tested in the suspension test achieved >4 log(10) redu ction in viable bacterial concentrations, apart from povidone iodine tested against Ent. faecalis and VRE. The antibacterial activity of biocides test ed in the glass-carrier test was significantly lower than in the suspension test, with the exception of triclosan in isopropanol, which was as effecti ve in both suspension and glass-carrier test. In the ex-vivo test, triclosa n in isopropanol achieved a log(10) reduction in viable bacterial concentra tion of 1.105-1.771 (,vith the exception of P. aeruginosa with 0.758 log(10 ) reduction). PCMX, povidone iodine and chlorhexidine achieved log(10) redu ctions in viable bacterial concentration of 0.303-0.901, Chlorhexidine test ed against P. aeruginosa produced a 1.94 log(10) reduction in concentration . These results confirm previous observations about the need for testing th e antimicrobial activity of antiseptics on skin surface to determine their in-situ efficacy and encourage further the use of the ex-vivo protocol.