[Susceptibility of methicillin-resistant Staphylococcus aureus to various antibiotics. Classification by...

MICs of 14 aminoglycoside antibiotics including 10 of those used clinically were determined against 50 strains of methicillin-resistant Staphylococcus aureus (MRSA) which had been isolated at a hospital in Osaka between 1986 and 1990. Arbekacin (ABK) inhibited the growth of all strains at less than or equal to 0.20-6.25 micrograms/ml, showing the most potent activities. Streptomycin showed good activities (1.56-6.25 micrograms/ml) against all strains except one resistant strain (greater than 100 micrograms/ml). Based on susceptibilities to kanamycin (98% resistant), tobramycin (84%), gentamicin (62%), amikacin (36%) and ABK (0%), MRSA strains were classified into 5 types; type 0 producing no aminoglycoside-modifying enzyme, type 1a producing APH(3'), type 1b producing AAD(4', 4''), type 2a producing APH (2'')/AAC(6') and APH(3'), and type 2b producing APH(2'')/AAC(6') and AAD(4', 4''). In addition to the aminoglycoside antibiotics, 13 known antibiotics including vancomycin (VCM) were found active against MRSA upon random screening. Taitomycin (0.013-0.050 micrograms/ml) was the most potent, and griseoluteins A and B (each 0.10-0.39 micrograms/ml), and macarbomycin (0.05-0.20 micrograms/ml) were more active than VCM (0.39-1.56 micrograms/ml). Novobiocin (less than or equal to 0.20-0.78 micrograms/ml) also showed good activities.