[Bacteriological evaluation of combined effects of vancomycin and beta-lactams. I. Results against...

We previously reported a part of the results we obtained regarding antibacteriological synergism between beta-lactams and vancomycin (VCM) against methicillin-resistant Staphylococcus aureus (MRSA). This paper reports an additional assessment we made subsequently to the previous report regarding antibacterial effects of different beta-lactams and VCM concurrently used against MRSA. Assessed in this study were bacteriological synergistic actions between flomoxef (FMOX) and VCM, latamoxef (LMOX) and VCM, cefpirome (CPR) and VCM and imipenem (IPM) and VCM against MRSA. 1. Synergistic enhancements of therapeutic activities were observed against MRSA with FMOX +VCM, CPR + VCM and IPM + VCM, but the activity of LMOX + VCM was low. 2. Concentration dependencies of actions of these antibiotic agents against MRSA were strong for beta-lactams, but weak for VCM. These observations were opposite of the results for beta-lactams and aminoglycosides, or beta-lactams and tetracyclines against MRSA we reported previously. 3. It appeared that strong synergistic antibacterial effects were obtained with FMOX or CPR concentrations between 8 and 32 micrograms/ml when used with VCM, and IPM concentrations between 4 and 16 micrograms/ml when used with VCM, hence, in the therapy using these combinations, concentrations and dose intervals of beta-lactams employed should be carefully considered. 4. When these antibiotics are used together in in vitro experiments, values of MIC and FIC-index may be different depending upon experimental systems used.