[Antibacterial activities of arbekacin against recently isolated methicillin-resistant Staphylococcus aureus (I)].

Against 200 strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated from 1990 to 1991, minimum inhibitory concentrations (MICs) of a total of 15 antibacterial agents including arbekacin (ABK) were determined. In addition coagulase types of the tested strains were determined and classified according on their origins. 1. Among the coagulase types of 200 strains, type II were 63.5%, type IV 18.5%, type VII 11.0% and the other types 7.0%. Type II strains were prevailing among those isolated from the respiratory tract specimens and type IV among those from the surgical specimens. These results were in agreement with other recent reports including our previous ones. 2. The MIC50 of methicillin, 6 cephalosporins (CEPs), imipenem, fosfomycin (FOM), gentamicin, tobramycin and clindamycin for 200 strains ranged from 50 to > 100 micrograms/ml. On the other hand, MIC50 and MIC90 of ABK, minocycline (MINO) and vancomycin (VCM) were 0.78 and 3.13 micrograms/ml for ABK, 0.39 and 50 micrograms/ml for MINO, and 0.78 and 1.56 micrograms/ml for VCM. 3. The MIC90 of ABK against coagulase type IV strains was rather high, 12.5 micrograms/ml. However, the strains inhibited by 6.25 to 12.5 micrograms/ml of ABK were isolated even in our studies performed in 1986, 1988 and 1989. Further studies are therefore required to confirm whether appearance of these strains used in the present study inhibited at relatively high concentrations of ABK is due to the use of ABK. 4. It is reported that, at present, most of the MRSAs spreading in Japan are acceleratedly acquiring resistance to many drugs, and especially, they are developing high resistance against beta-lactams. ABK showed potent antibacterial activities even against these strains. Since ABK has been shown to display potent activities against MRSA in combination with beta-lactams or FOM, we believe ABK is one of the useful aminoglycoside antibiotics for the treatment of MRSA infections.