[Antimicrobial activities of polymyxin B against clinically isolated microbial strains. Results of MIC determination including high concentrations].

Minimum inhibitory concentrations (MICs) were determined for polymyxin B (PL-B), gentamicin, ofloxacin and norfloxacin against clinically isolated microbial strains collected since November 1992, and the following conclusions were obtained: 1. Judging from the MIC distribution of PL-B against the studied strains including multi-drug resistant organisms of major strains of family Enterobacteriaceae, such as Escherichia coli, Klebsiella pneumoniae, Enterobacter spp., and Pseudomonas aeruginosa, it appeared that no PL-B resistant strains were detected among those Gram-negative organisms within the antimicrobial spectrum of PL-B. 2. MICs of PL-B against most strains including methicillin resistant Staphylococcus aureus and coagulase-negative staphylococci were distributed between 100 and 800 micrograms/ml. These results supported reports of other investigators that the eradication of Staphylococcus spp. including MRSA (methicillin-resistant S. aureus) was possible by the use of PL-B at 1 mg/ml. 3. MIC distribution of PL-B against organisms of the Bacteroides fragilis group was almost the same as the results described above.