322 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II In Vivo Antimicrobial Activity of Calcium Undecylenate Powder Against Several Microorganisms • Undecylenic Initial Microorganism acid powder Placebo p-value Inoculum size S. aureus 6.1 X 10 4 2.9 X 10 6 0.0005 1.9 X 109 CFU S. pyogenes 0 6.2 x 104 0.0545 3.8 x 10 v CFU C. albicans 6.4 X 10 3 2.5 X 104 0.1944 2.6 X 106 CFU P. aeruginosa 0.1 x 10 2.0 x 102 0.1705 3.0 x 106 CFU 'Overnight undiluted cultures were used for inoculation, except for Candida (which at high concentration size may initiate skin lesion), diluted to 105 to 10 6 dose level (observatiotl). activity between the test powder and the placebo was not significant against C. albicans and P. aeruginosa. DISCUSSION We have demonstrated on humans a simple quantitative in vivo method by which antimicrobial activity of a topical test product was measured against several organisms under occlusion. Since many bacteria are sensitive to dessication, semioocclusive devices are recommended to allow hydration and proliferation of microorganisms. Resident skin bacteria are most numerous in moist intertrigenous areas (6). On the glabrous skin, the bacterial population is around 1,000/cm 2. When skin is wrapped with occlusive plastic films, the level of bacterial growth is enormously increased to millions/cm 2 within 24 hr (1). In previous methods, polyvinylidine film (Saran Wrap) or other plastic dressings were placed on the test areas to provide occlusion (1,2). These occlusive devices were in intimate contact with the skin it is assumed that their removal would remove the adhering bacteria. The plastic weigh boats utilized in this study do not provide occlusion only. Since these dishes do not touch the test sites, bacterial counts would not be affected. These devices further permit up to four test organisms to be used on a single forearm (the other arm serving as the control). In this investigation, an antifungal ointment and powder was assayed for their antimicrobial activity in vivo. Undecylenic acid ointment has demonstrated significant antimicrobial activity against S. aureus, S. pyogenes, C. albicans and P. aeruginosa. We have shown that this compound used prophylactically for tinea pedis (athlete's foot) was not only antifungal but also antibacterial. Undecylenic acid powder was effective against S. aureus and S. pyogenes, but not against C. albicans and P. aeruginosa. The reduction of microbial counts in placebo group was noteworthy. This could be attributed to the inherent ability of skin to destroy artificially applied organisms (4). Although topical antifungals are prescribed for their effect on fungi, it has been postulated that bacteria also play an important role in the pathogenesis of certain human fungal infections (7,8,9). The new topical antifungals (imidazoles) have been chosen for clinical use for both their antifungal spectra and their antibacterial potency.

IN VIVO TESTING OF TOPICAL ANTIMICROBIALS 323 It appears that the older agent--undecylenic acid--chosen mainly for its antifungal effect, also has antibacterial potency. The numbers of organisms seeded in the experiments are comparable to those noted in some bacterially infected skin. It is possible that this may have a clinical effect--if bacteria indeed add to the pathology of fungal infections. REFERENCES (1) R. Aly, C. Shirley, R. Cunico and H. Maibach, Effect of prolonged occlusion on the microbial flora, pH, CO2 and transepidermal water loss on human skin,J. Invest. Dermatol., 71,378-381 (1978). (2) R. R. Marples and A.M. Kligman, Growth of bacteria under adhesive tapes. Arch. Dermatol., 99, 107-110 (1969). (3) R. Aly and H. Maibach, Clinical Skin Microbiology, (C. C. Thomas, 1978) pp 20-28. (4) P. Williamson and A.M. Kligman, A new method for the quantitative investigation of cutaneous flora,J. Invest. Dermatol., 45,498-503 (1965). (5) R. Aly, H. I. Maibach, W. G. Strauss and H. R. Shinefield, Survival of pathogenic microorganisms on human skin,J. Invest. Dermatol., 58, 205-210 (1972). (6) R. Aly and H. I. Maibach, Aerobic flora of intertrigenous skin, App. Environm. Microbiol., 33, 97-100 (1977). (7) A.M. Kligman and J. Leyden, The interaction of fungi and bacteria in the pathogenesis of athlete's foot, in Skin Bacteria: Relevance to Clinical Inaction, Eds. H. I. Maibach and R. Aly, (Springer Verlag 1981) (in press). (8) M. Marpies and M.J. Bailey, A search for the presence of pathogenic bacteria and fungi in the interdigital space of the foot, Brit. J. Dermatol., 69, 379-388 (1957). (9) D. Taplin, D.C. Bassett and P.M. Mertz, Foot lesions associated with Pseudomonas cepacia, Lancet, 2, 568-571 (1971).