An in Vitro Study of the Activity of Telithromycin against Mobile and Cystic Forms of Borrelia afzelii

In this study the new ketolide telithromycin was tested in vitro against motile and cystic forms of Borrelia afzelii, one of the species of Borrelia burgdorferi sensu lato. Acridine orange staining, dark field microscopy, and transmission electron microscopy were the techniques used to study the influence of telithromycin on the bacteria. The activity was unexpectedly high, 0.0003 microg/ml < MBC < or = 0.0006 microg/ml for the mobile forms after 7 days of incubation at 34 degrees C. MIC was < 0.00015 microg/ml. It is likely that the agent works bacteriostatically and kills in a time-dependent and concentration-independent way, by binding tightly to the ribosomes. The agent was not able to prevent cyst formation, and the cysts were not affect ed at an in vivo achievable concentration. Electron microscopy also supports the hypothesis of telithromycin being an effective agent against the mobile bacteria.