Influence of tetracyclines or cetylpyridinium bromide on activity of fluoroquinolones in Euglena gracilis.

To verify the hypothesis that the fluoroquinolone inhibitors of DNA gyrase generate some oxidant species and subsequently free radicals, the effects of simultaneous action of fluoroquinolones (ofloxacin, fleroxacin) and tetracyclines (tetracycline, doxycycline, thiatetracycline) or cetylpyridinium bromide as possible antioxidants on the flagellate Euglena gracilis were examined. Chloroplasts due to their bacterial character were injured and subsequently eliminated by fluoroquinolone. The loss of chloroplasts was accompanied by bleaching of originally green euglena cells. Tetracyclines, as well as cetylpyridinium bromide, decreased the euglena bleaching caused by ofloxacin or fleroxacin. The bleaching induced by ofloxacin or fleroxacin was most effectively inhibited by thiatetracycline and cetylpyridinium bromide. Control treating of cells with tetracyclines or cetylpyridinium bromide alone did not exert any bleaching effect. In vitro weak but significant interactions between examined substances were established as well.