What color indicates a positive reaction in an oxidase test?

A positive reaction in an oxidase test is indicated by the development of a blue color. The oxidase test is used to detect the presence of cytochrome oxidase, an enzyme found in some bacteria that is involved in the electron transport chain. When the oxidase reagent, typically consisting of tetramethyl-p-phenylenediamine, interacts with cytochrome oxidase, it becomes oxidized and produces a blue coloration.

This color change is significant as it confirms oxidative metabolism in the tested organism, helping to differentiate between species of bacteria. The absence of this blue color indicates a negative result, suggesting that cytochrome oxidase is not present in the organism being tested.

Understanding this color change is important for microbiologists as it assists in the identification and classification of bacteria based on their metabolic capabilities.