[Measurement of MICs on 16 antimicrobial agents for freshly isolated methicillin-resistant Staphylococcus aureus...

MICs of 16 antimicrobial agents including a newly synthesized aminoglycoside antibiotic, arbekacin (HBK), were determined against methicillin-resistant Staphylococcus aureus (MRSA) strains which had been isolated since 1988 from patients with refractory infections. 1. The proportion of highly methicillin-resistant strains was large, especially among those isolated from blood and respiratory tract. 2. All the MRSA strains were resistant to all the beta-lactam antibiotics tested. 3. Most of the strains were also resistant to aminoglycosides. However, HBK inhibited the growth of 95% of the strains at 3.13 micrograms/ml or less, showing potent activities even against highly resistant MRSA strains. 4. The MIC distribution of HBK against MRSA strains showed no change since 1986 when year to year data were compared. Based on our studies on the drug resistance pattern of MRSA since 1986, a large proportion of MRSA strains isolated from blood and respiratory tract appeared to be coagulase type II. 5. Netilmicin-resistant MRSAs have increased since 1986, and MRSA resistant to fosfomycin, minocycline, ofloxacin and norfloxacin have also increased in 1989 compared to 1988. 6. The drug resistance pattern of MRSA has been changing every year and they are acquiring multi-drug resistance. Thus, in the treatment of MRSA infections, it is very important to identify the drug susceptibility of MRSA quickly and accurately.