What is the principle of oxidase test?
Oxidase Test is based on the principle that certain bacteria produce indophenol blue from the oxidation of dimethyl-p-phenylenediamine and α-naphthol. In presence of the enzyme cytochrome oxidase (gram-negative bacteria), the N,N-dimethyl-p-phenylenediamine oxalate and α-naphthol react to indophenol blue.
What is the positive color reaction in modified oxidase test?
Microorganisms are oxidase positive when the color changes to dark purple within 5 to 10 seconds. Microorganisms are delayed oxidase positive when the color changes to purple within 60 to 90 seconds. Microorganisms are oxidase negative if the color does not change or it takes longer than 2 minutes.
What is the purpose of an oxidase test?
The oxidase test is used to identify bacteria that produce cytochrome c oxidase, an enzyme of the bacterial electron transport chain. (note: All bacteria that are oxidase positive are aerobic, and can use oxygen as a terminal electron acceptor in respiration. This does NOT mean that they are strict aerobes.
What reagent in the modified oxidase test that makes it different from the oxidase test?
Modified oxidase test is performed in the same manner as the oxidase test, except that the reagent is 6% tetramethyl phenylenediamine hydrochloride in dimethyl sulfoxide.
Is oxidase test selective or differential?
Jakes Microbiology LAB #2
| A | B |
|---|---|
| Is the Oxidase test Differential or Selective? | Differential |
| Is the Citrate test Differential or Selective? | Differential |
| Is the Phenylethyl alcohol test Differential or Selective? | Selective. |
| Is the Eosin Methylene blue agar Differential or Selective? | Both |
Which reagent is used in the oxidase test?
The oxidase test often uses a reagent, tetra-methyl- p-phenylenediamine dihydrochloride, as an artificial electron donor for cytochrome c. When the reagent is oxidized by cytochrome c, it changes from colorless to a dark blue or purple compound, indophenol blue.
How do you prepare oxidase test?
Prepare a 1.0% Kovac’s oxidase reagent by dissolving 0.1 g of tetramethyl-p- phenylenediamine dihydrochloride into 10 ml of sterile distilled water. 2. Mix well and then let stand for 15 minutes. The solution should be made fresh daily and the unused portion should be discarded.
What is a modified oxidase test?
The oxidase method was originally described by Kovacs in 1956 as a method of differentiating gram-negative bacilli. However, in 1981, Faller and Schleifer modified Kovacs’ oxidase reagent by utilizing a tetramethyl-pphenylenediamine (TMPD) in dimethyl sulfoxide (DMSO). This is referred to as the modified oxidase test.
Is oxidase and catalase test the same?
Oxidase is often used as a sloppy word, when cytochrome c oxidase is meant. Catalase + (Cat +) means that the bacterium has catalase, which converts hydrogene peroxid to oxygen and water. Oxidase + (Ox +) means that the bacterium has cytochrome c oxidase as terminal enzyme in the respiratory chain.
