Relative resistance to erythromycin in Chlamydia trachomatis.

Recent Chlamydia trachomatis isolates were tested in a tissue culture system for susceptibility to tetracycline, erythromycin, rosaramicin, rifampin, and clindamycin. Rifampin was the most active drug (minimal inhibitory concentration, less than or equal to 0.02 microgram/ml). Tetracycline and rasaramicin were highly active, with a concentration of less than or equal to 0.25 microgram/ml being chlamydicidal. Clindamycin was least active on a weight basis, requiring up to 16 microgram/ml to prevent the passage of chlamydiae into a drug-free tissue culture system. Relative resistance to erythromycin was detected; two isolates were capable of limited replication in 1 microgram/ml.