The BacTiter-Glo Microbial Cell Viability Assay is a homogeneous method for determining the number of viable microbial cells in culture based on quantitation of the ATP present. ATP is an indicator of metabolically active cells. The homogeneous assay procedure involves adding a single reagent (BacTiter-Glo Reagent) directly to bacterial cells cultured in medium and measuring luminescence. The homogeneous format reduces pipetting errors that may be introduced during the multiple steps required by other methods of ATP measurement. The formulation of the reagent supports bacterial cell lysis and generation of a luminescent signal in a homogeneous add-mix-measure format. The luminescent signal is proportional to the amount of ATP present, which is directly proportional to the number of viable cells in culture. The assay relies on the properties of a proprietary thermostable luciferase (Ultra-Glo Recombinant Luciferase) and a proprietary buffer formulation for extracting ATP from bacteria. The assay has been shown to detect a variety of bacteria and fungi.