A colorimetric method for the evaluation of anti-giardial drugs in vitro

The aim of this study was to develop a simple and reliable method to determine the viability of Giardia intestinalis after incubation with an anti-giardial agent by using a colorimetric method. Factors that may affect the optical density value were systematically evaluated. The most suitable conditions were obtained when G. intestinalis trophozoites, 5 × 10(5)cells/ml were incubated with the anti-giardial agent for 48 h. The culture medium was removed and trophozoites were immediately fixed by immersing the whole plate in absolute methanol for 2 min. The fixed trophozoites were then stained with 0.1% w/v methylene blue for 10 min, washed once by immersing the whole plate into distilled water. The dye was released by adding 0.1M hydrochloric acid solution (300 μl) and the optical density was read at 655 nm. The 50% inhibitory concentration values (IC(50)) of metronidazole, ornidazole and furazolidone obtained from our proposed method (0.41 ± 0.06, 0.18 ± 0.01, 0.26 ± 0.13 μg/ml, respectively) were comparable to the IC(50) values obtained by the current conventional method (0.14 ± 0.05, 0.15 ± 0.04, 0.14 ± 0.02 μg/ml, respectively). This new method did provide a convenient and reliable way to screen for potential anti-giardial agents.