HRE 664

To determine susceptibility to 31 old and new antimicrobials, 44 strains of Staphylococcus aureus, most resistant to oxacillin and ciprofloxacin and isolated in a community hospital, were tested in vitro. For the peptide/peptide-derivative compounds, with the exception of mersacidin, all strains were inhibited by less than or equal to 2 micrograms/ml. Minimum inhibitory concentration (MIC)90 values indicated mupirocin, teicoplanin, and MDL 62211 to be fourfold more active than vancomycin, ramoplanin, and decaplanin. For fluoroquinolones, ciprofloxacin-resistant S. aureus exhibited high-level cross-resistance to ofloxacin, norfloxacin, fleroxacin, enoxacin, and Ro 23-9424. WIN 57253, a new fluorinated naphthyridine, showed good activity against these strains. Among the beta-lactams, the penem-derivative compounds (imipenem, meropenem, FCE 22101, and HRE 664) had the greatest activity, although resistance to each compound was detected among oxacillin-resistant S. aureus. The presence of tazobactam reduced the piperacillin MIC90 fourfold. Oxacillin-susceptible strains were susceptible to cephalosporins/cephamycins, whereas most oxacillin-resistant strains exhibited resistance. This study has shown that certain old and new quinolones and peptide-derivative compounds have good in vitro activity against multiply resistant strains of S. aureus.