Tetracycline reduces fluoroquinolones-induced bleaching of Euglena gracilis

Inhibitory activity of tetracycline against ofloxacin- and fleroxacin-induced bleaching of green and etiolized Euglena gracilis was examined. Tetracycline hydrochloride in concentrations of 83-2079 μM in the light partially inhibited the bleaching activity of 83 μM ofloxacin and of 162 μM fleroxacin. In the dark, the TC inhibition of the fluoroquinolones-induced bleaching activity was most obvious, the white colony counts were all decreased. The total inhibition of bleaching was observed in 43 μM ofloxacin and 81 μM fleroxacin both in light and darkness. Cell growth was not significantly influenced by ofloxacin, fleroxacin and tetracycline in the light or darkness. Inhibition of ofloxacin-induced euglena bleaching by tetracycline was more effective in etiolized cells. TC at 0–416 μM did not influence the growth of ofloxacin (2.15 μM)-induced Salmonella typhimurium revertants.