Oxidase

General: Tests for the presence of cytochrome oxidase. Enterobacteriaceae are oxidase-, while Pseudomonadaceae are oxidase+ — this differentiation is perhaps the most common use of the test.

The test is performed using a fresh culture, reagent, and filter paper or a sterile swab. Specific techniques vary, but placement of fresh culture (NOT using a wire loop) on filter paper with reagent produces a rapid (<20 seconds) color change to purple if positive, and remains colorless if negative. However, reagent will slowly change color once thawed and exposed to room air.