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 antibacterial activity has often been well studied [1], their potential effectiveness on skin remains poorly documented. To date, in-vivo protocols designed for the testing of the antimicrobial efficacy of antiseptics cannot use, for ethical reasons, pathogenic bacteria or new formulations whose toxicity in human subjects is unknown. An 'ex-vivo' test was recently developed to overcome these problems. Freshly excised human skin from abdominal or breast 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 evaluated for their antimicrobial activity. Several micro-organisms were investigated: - Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Enterococcus faecalis, vancomycin-resistant Ent, faecium (VRE), S. epidermidis, Pseudomonas aeruginosa and Escherichia coli - with several biocides - para-chloro-meta-xylenol (PCMX, active compound of Dettol), povidone iodine, triclosan tin isopropanol) and chlorhexidine. Results from the ex-vivo test were compared with results obtained in suspension and glass-carrier tests. The bactericidal activity of the biocides depended upon the test performed and results were generally significantly different from one method to the other. All biocides tested in the suspension test achieved >4 log(10) reduction in viable bacterial concentrations, apart from povidone iodine tested against Ent. faecalis and VRE. The antibacterial activity of biocides tested in the glass-carrier test was significantly lower than in the suspension test, with the exception of triclosan in isopropanol, which was as effective in both suspension and glass-carrier test. In the ex-vivo test, triclosan in isopropanol achieved a log(10) reduction in viable bacterial concentration 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) reductions in viable bacterial concentration of 0.303-0.901, Chlorhexidine tested against P. aeruginosa produced a 1.94 log(10) reduction in concentration. These results confirm previous observations about the need for testing the antimicrobial activity of antiseptics on skin surface to determine their in-situ efficacy and encourage further the use of the ex-vivo protocol.