Oxidase test
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The oxidase test is a test used in microbiology to determine if a bacterium produces certain cytochrome c oxidases. It uses disks impregnated with a reagent such as N,N,N′,N′-Tetramethyl-p-phenylenediamine (TMPD) or N,N-Dimethyl-p-phenylenediamine (DMPD), which is also a redox indicator. The reagent is a dark blue to maroon color when oxidized, and colorless when reduced.
Strains may either be oxidase positive (OX+) or negative (OX-). OX+ normally means that the bacterium contains cytochrome c oxidase and can therefore utilize oxygen for energy production with an electron transfer chain.
Typically the Pseudomonadaceae are OX+ and Enterobacteriaceae are OX-. Another example is the preliminary identification of Neisseria and Moraxella genera, which are both oxidase positive, Gram-negative diplococci.
Procedures
- Wet each disk with about 4 inoculating loops of de-ionized water.
- Use a loop to aseptically transfer a large mass of pure bacteria to the disk.
- Observe the disk for up to 3 minutes. If the area of inoculation turns dark blue to maroon to almost black, then the result is positive. If a color change does not occur within three minutes, the result is negative.
Alternatively, live bacteria cultivated on trypticase soy agar plates may be prepared using sterile technique with a single-line streak inoculation. The inoculated plates are incubated at 37°C for 24-48 hours to establish colonies. Fresh bacterial preparations should be used. After colonies have grown on the media, two-to-three drops of the reagent DMPD is added to the surface of each organism to be tested. A positive test (OX+) will result in a color change to pink, through maroon and into black, within 10-30 seconds. A negative test (OX-) will result in a light pink coloration or absence of coloration.de:Oxidase-Test
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
