J. Cosmet. Sci., 63, 133–137 (March/April 2012) 133 UVc-irradiation sublethal stress does not alter antibiotic susceptibility of staphylococci (MRSA, MSSA, and coagulase-negative staphylococci) to β-lactam, macrolide, and fl uoroquinolone antibiotic agents YASUNORI MAEDA, COLIN E. GOLDSMITH, WILSON A. COULTER, B. CHERIE MILLAR, JAMES S. G. DOOLEY, COLM J. LOWERY, ANNE LOUGHREY, PAUL J. ROONEY, DAVID A. MCDOWELL, MOTOO MATSUDA, and JOHN E. MOORE, Northern Ireland Public Health Laboratory, Department of Bacteriology, Belfast City Hospital, Lisburn Road, Belfast, BT9 7AD, Northern Ireland, UK (Y.M., C.E.G., B.C.M., A.L., P.J.R., J.E.M.) School of Biomedical Sciences, University of Ulster, Cromore Road, Coleraine, BT52 1SA, Northern Ireland, UK (Y.M, J.S.G.D., C.J.L., J.E.M.) School of Dentistry, Queen’s University of Belfast, Royal Group of Hospitals, Grosvenor Road, Belfast, BT12 6BP Northern Ireland, UK (W.A.C.) Food Microbiology Research Group, School of Health Sciences, University of Ulster, Jordanstown, Newtownabbey, BT37 0QB, Northern Ireland, UK (D.A.MCD.) and Laboratory of Molecular Biology, School of Environmental Health Sciences, Azabu University, 1-17-71 Fuchinobe, Sagamihara, Kanagawa 229, Japan (M.M.). Accepted for publication September 21, 2011. Synopsis Skin tanning, either by exposure to natural sunlight or through use of UV sunbeds, has become a popu- lar practice in the US, where it is estimated that approximately 1 million times per day someone in the US uses UV radiation for skin tanning, equating to 30 million Americans (circa 10% of the US popula- tion) who use a tanning bed. As well as exposing the host to periods of UV radiation, such practices also expose commensal skin bacteria, including Staphylococcus aureus, to such UV radiation. Previous work has indicated that environmental stresses on bacteria may lead to an upregulation of stress responses, in an attempt for the organism to combat the applied stress and remain viable. UV light may act as an environmental stress on bacteria, and so it was the aim of this study to examine the effect of UVc light on the antibiotic susceptibility of commensal skin bacteria, to determine if UV radiation would increase Address all correspondence to John E. Moore at jemoore@niphl.dnet.co.uk.

JOURNAL OF COSMETIC SCIENCE 134 the antibiotic resistance of such skin fl ora and thus lead to a potential skin fl ora with increased antibi- otic resistance. Previously, it has been shown that UVc light has a greater mutational effect on bacteria compared to lower-energy UV forms, including UVa and UVb light. Therefore, we decided to employ UVc light in our study to amplify the potential for mutational events occurring in skin staphylococci and to then quantify such events pre- and post-exposure. Wild-type clinical staphylococci organisms (n=8) including methicillin-sensitive Staphylococcus aureus (n=2), methicillin-resistant Staphylococcus au- reus (n=4), and coagulase-negative staphylococci (Staphylococcus haemolyticus) (n=2) were exposed to vary- ing degrees of sublethal radiation via UVc light, and their minimum inhibitory concentration (MIC) susceptibility was determined by broth dilution assay against three classes of commonly used antibiot- ics, namely β–lactams (penicillin), macrolides (erythromycin), and fl uoroquinolones (ciprofl oxacin). There was no signifi cant difference between antibiotic susceptibility before UVc exposure and until maximum sublethal stress, prior to cell death due to fatal UVc exposure with the cells. These results indicate that UV environmental stress/exposure does not upregulate antibiotic resistance, and therefore these data indicate that UVc radiation does not lead to a more antibiotic-resistant population in the staphylococci organisms post-exposure. BACKGROUND Skin tanning has become a popular cosmetic activity in the US. A recent report in the New England Journal of Medicine (September 2010) has quantifi ed that approximately 30 million Americans (circa 10% of the US population) use a tanning bed and that there are over 1 million tanning events daily (1). While the debate rages on regarding the FDA’s classifi cation of such instruments and legislation of the use of tanning beds in relation to the development of skin cancers, particularly malignant melanoma, there has been little to no attention given to the effects of such UV radiation on the many commensal bacteria that constitute a healthy skin fl ora on the individual using the tanning bed. Recently published data from our group (2) and others (3) have demonstrated that when bacteria are exposed to environmental stresses, such as altered pH, heat shock, and in- creased salinity, antibiotic susceptibility is altered so that they become either more sus- ceptible to antibiotic agents or, conversely, more resistant to antibiotics. For example, when we sublethally stressed Staphylococcus aureus organisms with increased salt or pH, we observed up to a fourfold increase in MIC with gentamicin and erythromycin (2). There- fore, it is important to examine the effect of the UV radiation stress response, as UV light may act as an environmental stress on bacteria. Thus it was the aim of this study to exam- ine the effect of UVc light on the antibiotic susceptibility of commensal skin bacteria, to determine if UV radiation would increase the antibiotic resistance of such skin fl ora and thus lead to a potential skin fl ora with increased antibiotic resistance. Previously, it has been shown that UVc light has greater mutational effect on bacteria compared to lower-energy UV forms, including UVA and UVB light (4). Therefore, we decided to employ UVc light in our study to amplify the potential for mutational events occurring in skin staphylococci and to then quantify such events pre- and post-exposure. MATERIALS AND METHODS BACTERIAL ISOLATES Wild-type clinical staphylococci organisms (n=8), including methicillin-sensitive Staphylococ- cus aureus (n=2), methicillin-resistant S. aureus (n=4), and coagulase-negative staphylococci