Oxidase Test : This test is used to identify microorganisms containing the enzyme
cytochrome oxidase (important in the electron transport chain). It is commonly used to
distinguish between oxidase negative Enterobacteriaceae and oxidase positive
Pseudomadaceae. Cytochrome oxidase transfers electrons from the electron transport chain
to oxygen (the final electron acceptor) and reduces it to water. In the oxidase test, artificial
electron donors and acceptors are provided. When the electron donor is oxidized by
cytochrome oxidase it turns a dark purple. This is considered a negative result. The result
present negative result it’s assumed that E. coli can’t produce enzyme cytochrome oxidase.