Time-kill activity of the streptogramin NXL 103 against Gram-positive and -negative bacteria.

Against 33 Gram-positive and -negative bacteria, NXL 103 MICs were 0.03 to 1 μg/ml. NXL 103 was bactericidal by 12 h at 2 × MIC against all 5 pneumococci and at 2 × MIC after 24 h against all 5 group A and B β-hemolytic streptococci. NXL 103 was bactericidal against all 8 Haemophilus influenzae strains at 2 × MIC and all 5 Moraxella catarrhalis strains at 4 × MIC after 24 h but was mainly bacteriostatic against 5 methicillin-resistant Staphylococcus aureus strains. After the exposure of one strain of each species to NXL 103 for 10 daily subcultures, the MICs remained within ± 1 dilution.