In vitro antibacterial activity of fluoroquinolones against Porphyromonas gingivalis strains.
OBJECTIVE
The objective of the study was to evaluate the in vitro activity of ciprofloxacin, gatifloxacin and moxifloxacin against 16 Porphyromonas gingivalis strains.


METHODS
MICs of the quinolones were established by Etest and the agar dilution technique. Experiments focused on determination of the spontaneous mutation rate and the induction of resistant strains, using 0.25-fold MIC of antibiotic. Fragments of gyrA and gyrB as well as of parC were sequenced.


RESULTS
Moxifloxacin and gatifloxacin had very low MIC values. Subinhibitory concentrations of the fluoroquinolones rapidly induced mutations. The spontaneous mutation rate was strain- and quinolone-dependent; the lowest rate was encountered after moxifloxacin. The predicted serum concentrations of the quinolones were bactericidal to wild-type strains, but 100 mg/L of each tested quinolone was insufficient to kill a mutant exhibiting moderate resistance. Often the mutants exhibited high resistance to >/=32 mg/L. All these mutants bore a Ser-83-->Phe substitution in GyrA.


CONCLUSIONS
DNA gyrase is the primary target of fluoroquinolones in P. gingivalis. In terms of the achievable level in the gingival fluid and the MICs, moxifloxacin might prevent the development of resistance and may be an alternative in the antibiotic treatment of P. gingivalis-associated periodontitis.
Eick
Sigrun
S
Institute of Medical Microbiology, University Hospital, Semmelweisstrasse 4, D-07740 Jena, Germany. Sigrun.Eick@med.uni-jena.de
Schmitt
Andrea
A
Sachse
Svea
S
Schmidt
Karl-Hermann
KH
Pfister
Wolfgang
W
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001372:Aza Compounds / Q000494:pharmacology; D016866:Bacteroidaceae Infections / Q000382:microbiology; D027081:DNA Gyrase / Q000235:genetics; D017931:DNA Primers; D027101:DNA Topoisomerase IV / Q000235:genetics; D024881:Drug Resistance, Bacterial; D024841:Fluoroquinolones / Q000494:pharmacology*; D000077734:Gatifloxacin; D006801:Humans; D008826:Microbial Sensitivity Tests; D000077266:Moxifloxacin; D009154:Mutation; D010518:Periodontitis / Q000382:microbiology; D016966:Porphyromonas gingivalis / Q000187:drug effects*; D011804:Quinolines / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction
D000900:Anti-Bacterial Agents; D001372:Aza Compounds; D017931:DNA Primers; D024841:Fluoroquinolones; D011804:Quinolines; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase; D000077734:Gatifloxacin; D000077266:Moxifloxacin