PMA works by selectively penetrating nonviable microbial cells with compromised membranes and combining only with exposed DNA of nonviable bacteria. Once inside the cell, PMA intercalates into the double-stranded DNA and forms a covalent bond on exposure to intense light. 

When PMA is applied to a sample containing viable and nonviable bacteria, only the DNA of the nonviable bacteria with compromised membranes undergo modification. After PMA-treatment, only the DNA from viable bacteria is usable in qPCR, enabling researchers to obtain only the amplified DNA of living organisms.