Why is oxidase test performed

It is recommended to use colonies that are hours old. Older colonies may produce weaker reactions. MacFaddin, J. Biochemical Tests for the Identification of Medical Bacteria, 2nd ed. Student Health Center Manuals.

Request new password. Effective Date:. P urpose and Scope: Cytochrome containing organisms produce an intracellular oxidase enzyme. Products should not be used if there are any signs of deterioration or if the expiration date has passed. The expiration date applies to the product in its intact packaging when stored as directed.

Quality Control: QC is performed on each day the test is performed. When present, the cytochrome c oxidase oxidizes the reagent tetramethyl-p-phenylenediamine dihydrochloride to indophenols , a purple or dark blue color end product.

When the enzyme is not present, the reagent remains reduced and is colorless. All bacteria that are oxidase-positive are aerobic and can use oxygen as a terminal electron acceptor in respiration.

This does NOT mean that they are strict aerobes. Bacteria that are oxidase-negative may be anaerobic, aerobic, or facultative; the oxidase negative result just means that these organisms do not have the cytochrome c oxidase that oxidizes the test reagent. They may respire using other oxidases in electron transport. Oxidase test can be performed in various ways.

These include, but are not limited to, the filter paper test , filter paper spot test , direct plate method , and test tube method. Bacterial species showing positive and negative reactions should be run as controls at frequent intervals. There may be different types of oxidase enzymes produced by bacteria.

The colorless redox reagent, tetramethyl-p-phenylenediamine dihydrochloride or dimethyl can be used used in the test will detect the presence of the enzyme oxidase and, reacting with oxygen, turn a color. The oxidase reagent contains a chromogenic reducing agent, a compound that changes color when it becomes oxidised, so it acts as an artificial electron acceptor for the enzyme oxidase.

The oxidised reagent forms the colored compound indophenol blue. A positive reaction will usually occur within seconds, and will be a bluish-purple color that progressively becomes more purple.