Comparison of the in vitro activity of pristinamycin and quinupristin/dalfopristin against Streptococcus pneumoniae

The in vitro activity of quinupristin/dalfopristin, a new injectable streptogramin, and pristinamycin was evaluated against 200 recently isolated clinical Streptococcus pneumoniae strains expressing various degrees of susceptibility to penicillin G and erythromycin. MICs were determined by the agar dilution method. All strains were susceptible to pristinamycin irrespective of their susceptibility to penicillin G or erythromycin (MIC90: 0.25 mg/L for each phenotype). The activity of quinupristin/dalfopristin was slightly lower than that of pristinamycin against 42 penicillin G-susceptible/erythromycin-susceptible strains (MIC90: 0.5 mg/L), 13 penicillin G-susceptible/erythromycin-resistant strains (MIC90: 1 mg/L), 25 penicillin G-intermediate or -resistant/erythromycin-susceptible strains (MIC90: 0.5 mg/L) and 120 penicillin G-intermediate or -resistant/erythromycin-resistant strains (MIC90: 0.5 mg/L). The activity of both streptogramins was not significantly altered in case of erythromycin resistance. Thus, both streptogramins might be useful for the treatment of penumococcal infections, especially in cases of multiresistant strains.