Comparative in-vitro activities of teicoplanin, vancomycin, coumermycin and ciprofloxacin, alone and in combination with rifampicin or LM 427, against Staphylococcus aureus.

The bactericidal interactions in vitro of two antibiotics active at the cell wall (teicoplanin and vancomycin) or two inhibitors of DNA gyrase (coumermycin and ciprofloxacin) combined with two inhibitors of protein synthesis (rifampicin and LM 427) were assessed against five Staphylococcus aureus strains. The S. aureus isolates included two oxacillin-sensitive and three oxacillin-resistant strains. The concentrations tested covered the range usually obtained in the serum with recommended doses. Coumermycin + rifampicin or LM 427, and ciprofloxacin + rifampicin or LM 427 were antagonistic when the concentration of either drug was higher than the MIC, and additive when sub-MIC concentrations were tested. Teicoplanin or vancomycin + rifampicin or LM 427 produced variable results. Of the synergic combinations, 14 of 15 included teicoplanin. Of the antagonistic combinations, 20 of 33 included LM 427. Antagonism with LM 427 was due to the higher intrinsic activity of LM 427 alone than teicoplanin, vancomycin or rifampicin. Teicoplanin (20 mg/l) + rifampicin or LM 427 (1 mg/l) was synergic (9/10).