The key difference between positive and negative oxidase test is that positive oxidase test indicates the presence of cytochrome C oxidase in bacterium, whereas negative oxidase test indicates the absence of cytochrome C oxidase.
The term oxidase test is usually useful in microbiology and has applications in analytical chemistry as well. An oxidase test detects the presence of a cytochrome oxidase.
CONTENTS
1. Overview and Key Difference
2. What is an Oxidase Test
3. What is Positive Oxidase Test
4. What is Negative Oxidase Test
5. Side by Side Comparison – Positive vs Negative Oxidase Test in Tabular Form
6. Summary
What is an Oxidase Test?
Oxidase test is useful in determining whether a bacterium can produce cytochrome C oxidases or not. This analytical technique uses disks that are impregnated with reagents such as TMPD or DMPD. When oxidized, the reagent becomes blue to maroon colour. When it is in the reduced state, the reagent is colourless.
Figure 01: Color Changes in Oxidase Test
The bacterium containing cytochrome C oxidases can catalyze the transport of electrons from donor compounds such as NADH to electron acceptors such as oxygen. TMPD or the test reagent in oxidase test acts as the artificial electron donor; thus, the oxidized reagent gives a colour (by forming the coloured compound indophenol blue). Usually, oxidase-positive bacteria species include aerobic organisms (these organisms are capable of using oxygen as the terminal electron acceptor).
What is Positive Oxidase Test?
Positive oxidase test is an analytical technique in which we can determine the presence of bacteria containing cytochrome c oxidase enzyme. This is denoted as OX+. This type of bacteria can use oxygen for energy production through the conversion of oxygen gas into hydrogen peroxide or water via an electron transfer chain. Typically, the bacteria from Pseudomonasdaceae species are OX+. In addition, many Gram-negative bacteria, spiral curved rod-shaped bacteria such as Vibrio cholerae are oxidase positive.
What is Negative Oxidase Test?
Negative oxidase test is an analytical technique in which we can determine the absence of cytochrome c oxidase enzyme in a given bacteria sample. We can denote this term as OX-. This type of bacteria cannot use oxygen for energy production through an electron transfer chain. If not, these bacteria employ a different cytochrome form for the transfer of electrons to oxygen. Typically, Enterobacteriaceae are oxidase negative.
What is the Difference Between Positive and Negative Oxidase Test?
Oxidase tests are useful in determining whether a bacterium can produce cytochrome C oxidases or not. The key difference between positive and negative oxidase test is that positive oxidase test indicates the presence of cytochrome C oxidase in bacterium, whereas negative oxidase test indicates the absence of cytochrome C oxidase.
Moreover, in positive oxidase test, the colour change is from blue to maroon, while in negative oxidase test, a colour change does not occur. Many Gram-negative bacteria and spiral-curved, rod-shaped bacteria such as Vibrio cholerae are oxidase-positive while bacteria from Enterobacteriaceae species are oxidase-negative.
The following infographic summarizes the difference between positive and negative oxidase test in tabular form for side by side comparison.
Summary – Positive vs Negative Oxidase Test
Oxidase tests are useful in determining whether a bacterium can produce cytochrome C oxidases or not. The key difference between positive and negative oxidase test is that positive oxidase test indicates the presence of cytochrome C oxidase in bacterium, whereas negative oxidase test indicates the absence of cytochrome C oxidase. In positive oxidase test, the colour change is from blue to maroon, while in negative oxidase test, a colour change does not occur.
Reference:
Aryal, Sagar, et al. “Oxidase Test- Principle, Uses, Procedure, Types, Result Interpretation…” Microbiology Info.com, 26 Sept. 2018, Available here.
Image Courtesy:
1. “Cytoxydase” (CC BY-SA 3.0) via Commons Wikimedia