In-vitro antibacterial activity of RP 59500, a semisynthetic streptogramin, against Streptococcus pneumoniae.

The in-vitro activity of the new streptogramin RP 59500 was determined against 100 strains of Streptococcus pneumoniae. In all, 48 erythromycin-sensitive strains and 52 erythromycin-resistant strains were tested by an agar dilution method (MIC determination), 20 strains (eight erythromycin-sensitive and 12 erythromycin-resistant) were tested by a broth microdilution technique (MIC and MBC determination) and ten strains (two erythromycin-sensitive and eight erythromycin-resistant) were tested for bactericidal kinetics. The study showed that RP 59500 had good bacteristatic and bactericidal activity against both erythromycin-sensitive and erythromycin-resistant strains. On the basis of these results, and because the number of erythromycin-resistant strains of S. pneumoniae isolated in France has increased steadily since 1985, RP 59500 might be useful for the treatment of pneumococcal infections and warrants further investigation.