[Evaluation of the activity and effects of combinations of various antibacterial agents against methicillin-resistant Staphylococcus aureus in vitro].

MICs of various antibacterial agents against methicillin-resistant Staphylococcus aureus (MRSA) were measured. Furthermore, we evaluated the effects of combinations of antibacterial agents against MRSA in vitro. In 24 cases out of 37, in which MRSA was isolated from inpatients, other microorganisms, such as Candida spp., Entrococcus spp., and Pseudomonas aeruginosa, were simultaneously isolated. From the results of minimum inhibitory concentrations (MICs), obtained from micro broth-dilution method, of various antibacterial agents against MRSA, range of MICs of arbekacin (ABK), vancomycin (VCM) and teicoplanin (TEIC) were < or = 0.25-4.0, 0.5-1.0 and 0.25-4.0 micrograms/ml respectively, and no strains of MRSA showed resistance to ABK, VCM and TEIC, so that we concluded that these three antibacterial agents were effective for MRSA infection. On the in vitro study of combination-effect of antibacterial agents, significant synergistic effects were achieved in the combination of VCM and flomoxef (FMOX) (Synergism rate was 97.3%) or VCM and imipenem (IPM) (Synergism rate was 97.2%). From the results that the fractional inhibitory concentration index in the combination of VCM with IPM was smaller than that with FMOX and that P. aeruginosa or Enterococcus spp. were simultaneously isolated in high frequency in the MRSA-isolated cases, we thought that the combination of VCM with IPM is more useful, because IPM is effective against P. aeruginosa but FMOX is not.