The oxidase test is a test used in microbiology to determine if a bacterium produces certain cytochrome c oxidases.[1] It uses disks impregnated with a reagent such as N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) or N,N-dimethyl-p-phenylenediamine (DMPD), which is also a redox indicator.