In vitro susceptibility of 7.5-kb common plasmid-free Chlamydia trachomatis strains.

Using a new plaque cloning technique, we obtained unique Chlamydia trachomatis strains which were confirmed to be free of the 7.5-kb common plasmid and glycogen in inclusions. The in vitro susceptibility of these strains to various chemotherapeutic agents was tested by comparison with their parent strains and clinical isolates possessing the common plasmid. No difference was detected for any of the agents tested, indicating that the 7.5-kb common plasmid is unrelated to the drug resistance of C. trachomatis.