BACKGROUND: Most strains of methicillin-resistant Staphylococcus aureus (MRSA) now exhibit high-level resistance to various antibiotics, such as beta-lactam antibiotics, aminoglycosides, macrolides, tetracyclines and quinolones. Recent reports describing the therapeutic failure of vancomycin for MRSA infections have arisen considerable concerns regarding the emergence of MRSA strains, which will require new therapeutic agents. Arbekacin, an aminoglycoside antibiotic, has antibacterial activity against both gram-positive and gram-negative bacteria and is stable in the presence of aminoglycoside inactivating enzymes produced by S. aureus. In this study, we compared the antibacterial activity of arbekacin with those of vancomycin, gentamicin, and amikacin against Staphylococcus aureus (S. aureus) and coagulase-negative staphylococci (CNS). METHODS: For a collection of 549 S. aureus and 251 CNS isolates from three Catholic University Hospitals in Korea, minimum inhibitory concentrations (MICs) of arbekacin, vancomycin, amikacin and gentamicin were determined by agar dilution method using Mueller-Hinton agar according to NCCLS (National Committee for Clinical Laboratory Standards, USA) criteria. RESULTS: Among 549 S. aureus isolates, 278 isolates were MRSA and 271 isolates were methicillin- sensitive S. aureus (MSSA). MIC50 & MIC90 of arbekacin against 549 S. aureus were 0.5 & 1 microgram/mL, and MIC50 & MIC90 of vancomycin were 1 & 1 microgram/ mL. MIC of arbekacin against 549 S. aureus isolates ranges from 0.03 to 4 microgram/mL, and MIC of vancomycin against 549 S. aureus ranges from 0.25 to 2 microgram/ mL. MIC90 of amikacin against 549 S. aureus was 32 microgram/mL, and that of gentamicin was 128 microgram/mL. MICs of amikacin and gentamicin were variable, ranging from 0.125 to 256, and otherwise arbekacin and vancomycin revealed relatively narrow range of MICs. MIC90 of arbekacin against 278 MRSA isolates & 271 MSSA were 1 & 0.5 microgram/mL, and those of vancomycin against MRSA & MSSA were 1 & 1 microgram/mL. MIC90 of amikacin against 278 MRSA & 271 MSSA isolates were 32 & 4 microgram/mL, and that of gentamicin against MRSA & MSSA isolates were 128 & 32 microgram/ mL respectively. Among 251 CNS isolates, 122 isolates were MRCNS and 129 were MSCNS. MIC50 & MIC90 of arbekacin against 251 CNS isolates were 0.25 & 2 microgram/mL, and those of vancomycin were 1 & 2 microgram/mL. MIC of arbekacin against 251 CNS isolates ranges from 0.015 to 32 microgram/mL, and that of vancomycin isolates ranges from 0.25 to 2 microgram/mL. MIC90 of arbekacin against 122 MRCNS & 129 MSCNS isolates were 2 & 0.5 microgram/mL, and those of vancomycin were 2 & 2 microgram/mL. MIC90 of amikacin against 251 CNS isolates was 32 microgram/mL, and that of gentamicin was 128 microgram/mL for CNS. MIC90 of amikacin against 122 MRCNS & 129 MSCNS isolates were 128 & 8 microgram/mL, and those of gentamicin were 256 & 32 microgram/ mL. CONCLUSION: Considering above results, arbekacin can be a useful agent against most strains of MRSA and MRCNS, which exhibit high-level resistance to amikacin and gentamicin.