In vitro activities of fluoroquinolones against the spirochete Borrelia burgdorferi

Little is known to date about the in vitro activity of fluoroquinolones aga inst Borrelia species. Our study aimed at determining the in vitro activiti es of 15 quinolones against nine isolates of the Borrelia burgdorferi sensu lato complex in addition to one Borrelia valaisiana and one Borrelia bisse ttii tick isolate. For the determination of MICs, a standardized colorimetr ic microdilution method was applied. Determination of minimal borreliacidal concentrations providing 100% killing of the final inoculum (MBCs) after 7 2 h and time-kill experiments were performed by conventional culture in Bar bour-Stoenner-Kelly medium in combination with dark-field microscopy. The r ank order of potency on a microgram-per-milliliter basis for the substances with in vitro activity against B. burgdorferi was gemifloxacin (MIC at whi ch 90%, of the isolates tested are inhibited [MIC90], 0.12 mug/ml) > sitafl oxacin (MIC90 0.5 mug/ml), grepafloxacin (MIC90, 0.5 mug/ml) > gatifloxacin (MIC90, 1 mug/ml), sparfloxacin (MIC90, 1 mug/ml), trovafloxacin (MIC90, 1 mug/ml) > moxifloxacin (MIC90, 2 mug/ml), ciprofloxacin (MIC90, 2 mug/ml) > levofloxacin (MIC90, 4 mug/ml) > ofloxacin (MIC90, 8 mug/ml), norfloxacin (MIC90, 8 mug/ml) > fleroxacin (MIC90, > 16 mug/ml), and pefloxacin (MIC90 , 32 mug/ml) > nalidixic acid (MIC90, 256 mug/ml). After 72 h of exposure, gemifloxacin was borreliacidal (100% killing) against the isolates investig ated at a median MBC of 4 mug/ml. In the other compounds tested, median MBC s were higher (greater than or equal to8 mug/ml). Results of electron micro scopy and time-kill studies clearly support an in vitro activity of some fl uoroquinolones against borreliae. Our study demonstrates for the first time the enhanced in vitro effectiveness of some of the recently introduced 4-q uinolones against B. burgdorferi.