a method for detecting a microorganism by coloration is provided that includes adding and reacting , in a liquid culture medium , an alkaline sensitizing solution and a coloring reagent containing a redox dye , the liquid culture medium having been inoculated with a test sample , thereby detecting the microorganism by coloration in the reaction . there is also provided a method for testing drug susceptibility of a microorganism using above - mentioned method . furthermore , kits used in these methods are provided . the invention is useful to assess readily and objectively the growth of microorganism when carrying out e . g . a detection of microorganism in foods and a test such as a drug susceptibility test .