In-vitro microbiological activities of DuP 105 and DuP 721, novel synthetic oxazolidinones.

DuP 105 and 721, synthetic antibiotics belonging to a totally novel chemical class (oxazolidinones), have been found to be active in vitro against a wide range of Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus. DuP 721 had geometric mean MICs ranging from 1.1 to 16 mg/l against 167 strains of Staph. aureus, Staph. epidermidis, Staph. saprophyticus, streptococci of Groups A, B and D and diphtheroids. DuP 105 was between 1.5 and eight-fold less active. Bacteroides fragilis strains were also susceptible to the DuP compounds (mean MICs being 8.3 and 14.9 mg/l for DuP 721 and 105, respectively), but other Gram-negative species and yeasts were not inhibited by concentrations in excess of 100 mg/l. Both compounds had a predominantly bacteriostatic action. No primary resistance was found, and the incidence of resistant variants in 105 strains tested was less than 1 per 10(8) bacteria.