SY Park, et al Ann Dermatol Vol. 24, No 1, 2012 ORIGINAL ARTICLE http://dx.doi.org/10.5021/ad.2012.24.1.32 The Prevalence, Genotype and Antimicrobial Susceptibility of High- and Low-Level Mupirocin Resistant Methicillin-Resistant Staphylococcus aureus Se Young Park, M.D.1, Shin Moo Kim, Ph.D.2, Seok Don Park, M.D., Ph.D.1,3 1Department of Dermatology, Wonkwang University School of Medicine, 2Department of Clinical Laboratory Science, Wonkwang Health Science University, 3Institute of Wonkwang Medical Science, Wonkwang University School of Medicine, Iksan, Korea Background: Mupirocin has been used for the treatment of skin infections and eradication of nasal carriage of methicil- lin-resistant Staphylococcus aureus (MRSA). The increased use of this antibiotic has been accompanied by outbreaks of MRSA that are resistant to mupirocin. Objective: This study aims to determine the prevalence, genotype and antimicrobial susceptibility of mupirocin-resistant MRSA from 4 Korean hospitals. Methods: A total 193 MRSA clinical isolates were collected from four university hospitals. Antimicrobial sus- ceptibility tests, including mupirocin, and pulsed-field gel electrophoresis (PFGE) pattern analysis were performed. Results: Overall, 27 of the 193 (14.1%) MRSA isolates were resistant to mupirocin. All of the (A) hospital isolates showed high-level (HL) mupirocin resistance and the low-level (LL) mupirocin resistant strains were from three other hospitals. The PFGE patterns of 16 mupirocin-resistant isolates were divided into 5 clusters (1-5), and the nine HL mupirocin- resistant isolates belonged to cluster 1. Both the HL and LL mupirocin-resistant MRSA isolates were susceptible to van- comycin and rifampin, but they were resistant to ciproflo- xacin, clindamycin and tetracycline. The erythromycin and fusidic acid resistance rates were different between the HL and LL resistant isolates. Conclusion: HL mupirocin-resistant isolates that could transfer this resistance to other bacteria Received April 27, 2011, Revised July 5, 2011, Accepted for publication July 7, 2011 Corresponding author: Seok Don Park, M.D., Ph.D., Department of Dermatology, Wonkwang University Hospital, 344-2 Sinyong-dong, Iksan 570-711, Korea. Tel: 82-63-859-1601, Fax: 82-63-842-1895, E-mail: sdpark@wonkwang.ac.kr This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 32 Ann Dermatol were detected and these isolates were clonally related. The emergence of mupirocin resistant isolates emphasizes the importance of using antibiotics judiciously and carefully monitoring the prevalence of mupirocin resistance. (Ann Dermatol 24(1) 32∼38, 2012) -Keywords- Antimicrobial susceptibility, MRSA, Mupirocin, Pulsed field gel electrophoresis INTRODUCTION Mupirocin is a topical antibiotic that was originally isolated from Pseudomonas fluorescens, and it inhibits bacterial protein synthesis by competitively binding to isoleucyl- tRNA synthetase (IleS). This drug is particularly effective against streptococci and staphylococci, including methicil- lin-resistant Staphylococcus aureus (MRSA). Mupirocin is one of the most popular topical agents used for the treat- ment of skin infection and eradication of nasal carriage of MRSA1. The increased use of this antibiotic has been accompanied by outbreaks of MRSA that are resistant to mupirocin2. The mupirocin resistant strains are divided into two groups depending on the minimum inhibitory concentra- tion (MIC) against mupirocin: low-level resistance (MIC=8 ∼256μg/ml) and high-level resistance (MIC＞256μg/ ml). High-level mupirocin resistant strains are important in the clinical field because they are able to transfer resistance genes to other bacteria by plasmid conjugation, conse- quently protecting these bacteria from being eradicated with mupirocin3. The use of mupirocin ointment has been increasing in