The BacLight™ RedoxSensor™ CTC Vitality Kit provides effective reagents for evaluating bacterial cell health and vitality that can withstand fixation procedures. Briefly, healthy cells respiring via the electron transport chain will absorb and reduce CTC into an insoluble, red fluorescent formazan product. Cells not respiring or respiring at slower rates will reduce less CTC and consequently produce less fluorescent product, giving a semi-quantitative estimate of healthy vs. unhealthy bacteria. Green- and blue-fluorescent nucleic acid stains are included as counterstains to assist differentiation of cells from debris and calculating total cell numbers.