A comparison of the in-vitro activity of antimicrobials against Chlamydia trachomatis examined by Giemsa and a fluorescent antibody stain.

Minimum concentrations for the inhibition of normal chlamydial inclusions (MICN) and abnormal inclusions (MICA) were obtained for a range of antimicrobials titrated against Chlamydia trachomatis in McCoy cell cultures. Each antibiotic titrated produced an MICN which was the same whether examined by Giemsa or fluorescent antibody staining methods (rifampicin 0.007 mg/l, tetracycline, erythromycin and penicillin 0.062 mg/l, chloramphenicol and spiramycin 0.25 mg/l, ciprofloxacin 1.0 mg/l, and cycloserine 250 mg/l). With the exception of penicillin the MICA (Giemsa) was between two- and four-fold higher than the MICN, and the MICA (fluorescent antibody) a further two-fold higher. Penicillin was alone in the wide concentration range over which abnormal inclusions were detected (0.0062 mg/l to 5 g/l).