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In Vitro Activities of Daptomycin Against Recent Clinical Isolates ofMethicillin-resistant Staphylococci and Vancomycin-resistant Enterococci in Korea
Hyukmin Lee, M.D.1,3, Seo-Jin Park, M.D.2, Yeoung Seon Choi3, Doe-Young Park3, Kyoung Ho Roh, M.D.2,3Jong Hwa Yum, Ph.D.2,3, Dongeun Yong, M.D.2,3, Kyungwon Lee, M.D.2,3, and Yun Sop Chong, Ph.D.2,3
1Department of Laboratory Medicine, Kwandong University College of Medicine, Kyunggi, Korea2Department of Laboratory Medicine and 3Research Institute of Bacterial ResistanceYonsei University College of Medicine, Seoul, Korea
Vol.38 Num.2 (p85~90)
Background:Daptomycin is a novel cyclic lipopeptide antibiotic that exhibits in vitro bactericidal activity against gram-positive pathogens including methicillin-resistant staphylococci and vancomycin-resistant enterococci. The aim of this study is to determine the in vitro activities of daptomycin against recent clinical isolates of methicillin-resistant staphylococci and vancomycin-resistant enterococci in Korea.
Materials and Methods:A total of 117 clinical strains of methicillin-resistant staphylococci and vancomycin-resistant enterococci were isolated at a tertiary-care hospital in Korea in 2004. Susceptibility to daptomycin was tested by the CLSI broth microdilution method using Mueller-Hinton broth (MHB) which was adjusted to contain a final concentration of 50 ?g/mL of ionized calcium (Ca2+). Susceptibilities to ampicillin, oxacillin, levofloxacin, vancomycin, and linezolid were tested by the CLSI agar dilution method.
Results:All isolates of methicillin-resistant S. aureus and coagulase-negative staphylococci were inhibited by 1 ?g/mL of daptomycin, and MIC90s were 1 ?g/mL, which were similar to those of vancomycin and linezolid. MIC90s of daptomycin for vancomycin-resistant E. faecalis and E. faecium were 0.5 ?g/mL and 2 ?g/mL, respectively, and all isolates were susceptible to daptomycin. MIC90s of linezolid and levofloxacin for vancomycin-resistant enterococci were 1-2 ?g/mL and 64 ?g/mL, respectively. Resistance rates of vancomycin-resistant E. faecalis and E. faecium to levofloxacin were 100% and 96%, respectively. Daptomycin MICs in MHB supplemented to 20-25 ?g/ml of Ca2+ were 2-8 fold higher than those in MHB supplemented to 50 ?g/mL of Ca2+.
Conclusion:Daptomycin is very active in vitro against methicillin-resistant staphylococci and vancomycin-resistant enterococci isolated in Korea, and it is important to test in vitro activity of daptomycin using MHB containing 50 ?g/mL of Ca2+.
Keywords : Daptomycin, MRSA, VRE, Staphylococci, Enterococci