The susceptibility to arbekacin (ABK) of methicillin-resistant Staphylococcus 
aureus (MRSA) was investigated to find out how it related to aac(6')/aph(2") 
gene. In 49 isolates of MRSA for which MIC of ABK ranged from 0.125 to 64 
micrograms/ml, the MICs of ABK for 38 strains carrying aac(6')/aph(2") gene were 
widely distributed from 0.25 to 64, whereas those for 11 strains without that 
gene were all < or = 0.5 microgram/ml. Residual rate of ABK activity was higher 
than that of gentamicin after the reaction with each crude enzyme preparation 
extracted from 3 isolates of MRSA, carrying aac(6')/aph(2") and aad(4',4") 
genes. Furthermore, 97 strains of MRSA isolated at Kanagawa prefecture in Japan 
in 1999 were all sensitive to ABK, although 28 strains of them carried 
aac(6')/aph(2") gene. These results showed that ABK resistance was not 
necessarily related to carrying aac(6')/aph(2") gene in clinical isolates of 
MRSA.