The oxidase test is a test used in microbiology

Microbiology

Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...

 to determine if a bacterium produces certain cytochrome c oxidase

Cytochrome c oxidase

The enzyme cytochrome c oxidase or Complex IV is a large transmembrane protein complex found in bacteria and the mitochondrion.It is the last enzyme in the respiratory electron transport chain of mitochondria located in the mitochondrial membrane...

s. It uses disks impregnated with a reagent

Reagent

A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...

 such as N,N,N′,N′-tetramethyl-p-phenylenediamine

Wurster's blue

Wurster's blue is the trivial name given to the chemical N,N,N′,N′-tetramethyl-p-phenylenediamine, also known as TMPD. It is an easily oxidised phenylenediamine, which loses two electrons in one-electron oxidation steps; the radical cation is a characteristic blue-violet colour, which gives the...

 (TMPD) or N,N-Dimethyl-p-phenylenediamine (DMPD), which is also a redox

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 indicator. The reagent is a dark blue to maroon

Maroon (color)

Maroon is a dark red color.-Etymology:Maroon is derived from French marron .The first recorded use of maroon as a color name in English was in 1789.-Maroon :...

 color when oxidized, and colorless when reduced.Oxidase positive bacteria possess cytochrome oxidase or indophenol oxidase (an iron containing
hemoprotein). These both catalyze the transport of electrons from donor compounds (NADH) to
electron acceptors (usually oxygen).
The test reagent, N, N, N’, N’-tetra-methyl-p-phenylenediamine dihydrochloride acts as an artificial
electron donor for the enzyme oxidase. The oxidized reagent forms the colored compound
indophenol blue.
The cytochrome system is usually only present in aerobic organisms which are capable of utilizing
oxygen as the final hydrogen receptor. The end product of this metabolism is either water or hydrogen
peroxide (broken down by catalase).

OX+

OX+ normally means that the bacterium contains cytochrome c oxidase and can therefore utilize oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 for energy production with an electron transfer chain.

Typically the Pseudomonadaceae

Pseudomonadaceae

The Pseudomonadaceae is a family of bacteria that includes the genera Azomonas, Azomonotrichon, Azorhizophilus, Azotobacter, Cellvibrio, Mesophilobacter, Pseudomonas , Rhizobacter, Rugamonas, and Serpens...

 are OX+

Another example is the preliminary identification of Neisseria

Neisseria

The Neisseria is a large genus of commensal bacteria that colonize the mucosal surfaces of many animals. Of the 11 species that colonize humans, only two are pathogens. N. meningitidis and N. gonorrhoeae often cause asymptomatic infections, a commensal-like behavior...

and Moraxella

Moraxella

Moraxella is a genus of Gram-negative bacteria in the Moraxellaceae family. It is named after the Swiss ophthalmologist Victor Morax. The organisms are short rods, coccobacilli or, as in the case of Moraxella catarrhalis, diplococci in morphology, with asaccharolytic, oxidase-positive and...

genera, which are both oxidase positive, Gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

 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

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 for energy production with an electron transfer chain.

Typically Enterobacteriaceae

Enterobacteriaceae

The Enterobacteriaceae is a large family of bacteria that includes many of the more familiar pathogens, such as Salmonella, Escherichia coli, Yersinia pestis, Klebsiella and Shigella. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the...

 are OX-.

Procedures

1. Wet each disk with about 4 inoculating loops of de-ionized water.
2. Use a loop to aseptically transfer a large mass of pure bacteria to the disk.
3. 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

Trypticase soy agar

Trypticase soy agar is a bacterial growth medium.The medium contains enzymatic digests of casein and soybean meal which provides amino acids and other nitrogenous substances making it a nutritious medium for a variety of organisms. Glucose is the energy source. Sodium chloride maintains the osmotic...

 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.

External links

• Oxidase test video
• Oxidase Test Procedure