The Gordon Mcleod reagent (oxidase reagent) is used to carry out the oxidase test, to determine the presence of oxidase enzymes. The oxidase test, originally devised to identify all Neisseria spp., was later used to distinguish the Pseudomonadaceae from the oxidase - negative members of the Enterobacteriaceae.In the presence of atmospheric oxygen, cytochrome c, and an oxidase reagent, oxidize the reagent to a colored compound, indophenol. Neisseria gonorrhoeae ATCC 19424 Deep purple to blue Positive ; Staphylococcus aureus ATCC 25923 No colour change Negative