Abstract:Optimized conditions of methythiazol tetrazolium and resazurin assays for detection of antibacterial activities of bactericides were established by evaluating influences of the concentration of Ralstonia solanacearum and Xanthomonas citri pv. citri, the concentration of methythiazol tetrazolium and resazurin, and reaction time of bactericide with bacteria on the optical density. The results showed that optimized conditions of methythiazol tetrazolium and resazurin assays were that bacterial concentration was 105-106 CFU/mL, methythiazol tetrazolium concentration was 0.5 mg/mL, resazurin concentration was 0.02 mg/mL and reaction time of bactericide was 16-24 h. The antibacterial activities of some plant extracts and separating constituents against the two bacterial pathogens were detected by methythiazol tetrazolium and resazurin methods, and the results were consistent. The minimal inhibitory concentration of colorless compound EE-1 and khaki compound EE-2 against R.solanacearum were respectively 10 μg/mL and 20 μg/mL by using the two methods, which showed the same result. It could be concluded that antibacterial activity of micro-quantitative plant constituents could be tested fast and precisely by using methythiazol tetrazolium and resazurin assays.