Abstract
Four different compounds belonging to the macrolide-lincosamide-streptogramin B (MLS b ) class of antimicrobial agents were tested against 611 Streptococcus pneumoniae strains. The ketolide (HMR 3647, previously RU66647) and the streptogramin (quinupristin-dalfopristin) were both active against pneumococci with high-level MLS b resistance (clindamycin-resistant strains) as well as those with low-level macrolide resistance (clindamycin-susceptible strains).