Antimicrobial Activity of Several Antibiotics and a Sulfonamide Against Chlamydia trachomatis Organisms in Cell Culture

Minimum inhibitory concentrations of several antibiotics and a sulfonamide for growth of the 15 known immunotypes of Chlamydia trachomatis were determined in HeLa 229 cell cultures. The concentrations for complete inhibition of infectious-organism production were (per milliliter): tetracycline, 0.02 to 0.5 μg; rosamicin, 0.05 to 0.25 μg; erythromycin, 0.1 to 0.5 μg; chloramphenicol, 10 μg; penicillin, 0.02 to 50 U; ampicillin, 0.1 to 50 μg; and sulfisoxazole, 2 to 200 μg. The same concentrations of tetracycline, rosamicin, erythromycin, and chloramphenicol were sufficient to inhibit C. trachomatis inclusion formation. An increased concentration of sulfisoxazole was often needed to inhibit inclusion formation. Penicillin at 100 U/ml and ampicillin at 100 μg/ml failed to completely inhibit inclusion formation.