Propidium monoazide

Propidium monoazide (PMA) is a photoreactive DNA-binding dye that preferentially binds to dsDNA. It is used to detect viable microorganisms by qPCR. Visible light (high power halogen lamps or specific LED devices) induces a photoreaction of the chemical that will lead to a covalent bond with PMA and the dsDNA. This process renders the DNA insoluble and results in its loss during subsequent genomic DNA extraction. Theoretically, dead microorganisms lose their capability to maintain their membranes intact, which leaves the 'naked' DNA in the cytosol ready to react with PMA. DNA of living organisms are not exposed to the PMA, as they have an intact cell membrane. After treatment with the chemical, only the DNA from living bacteria is usable in qPCR, allowing to obtain only the amplified DNA of living organisms. This is helpful in determining which pathogens are active in specific samples. The main use of PMA is in Viability PCR but the same principle can be applied in flow cytometry or fluorescence microscopy.