Oxidase test

Background: 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.

Strains may either be oxidase positive (OX+) or negative (OX-).

OX+

OX+ normally means that the b

acterium contains cytochrome c oxidase and can therefore utilize oxygen for energy production with an electron transfer chain. Typically the Pseudomonadaceae are OX+[citation needed] Another example is the preliminary identification of Neisseria and Moraxella genera, which are both oxidase positive, Gram-negative diplococci.

Many Gram-negative spiral curved rods are also oxidase positive, which includes Helicobacter pylori, Vibrio cholera, and Campylobacter jejuni.

Also Legionella pneumophila is oxidase positive. A trick to remember the most medical relevant bacteria is: "VIce President CHeNEy MOstly LEads" (Vibrio, Pseudomonas, Campylobacter, Helicobacter, Neisseria, Moraxella, and Legionella, respectively).

OX-

OX- normally

means that the bacterium does not contain cytochrome c oxidase and therefore cannot utilize oxygen for energy production with an electron transfer chain. Typically Enterobacteriaceae are OX-.

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.