The bacteria that causes diphtheria, Corynebacterium diphtheriae, is a rod-shaped, non-spore-forming, Gram-positive bacterium. To distinguish Corynebacterium diphtheriae from other Corynebacterium species and similar bacteria, a variety of biochemical assays are employed.
Table of Contents
The following are a few typical biochemical assays used to identify Corynebacterium diphtheriae:
Key Tests
1. Gram Stain
Gram-positive rods that resemble Chinese characters, or “palisade” arrangements, are the typical form of C. diphtheriae.
2. Catalase Test
Positive Catalase is an enzyme produced by C. diphtheriae that converts hydrogen peroxide to oxygen and water. Every Corynebacterium species that has the potential to be toxic, including C. diphtheriae, is catalase positive. This indicates that they generate the catalase enzyme, which degrades hydrogen peroxide.
3. Oxidase Test
In the negative. Cytochrome oxidase is not produced by Corynebacterium diphtheriae.
4. Urease Test
In the negative. Cytochrome oxidase is not produced by Corynebacterium diphtheriae. Because C. diphtheriae lacks the urease enzyme, which breaks down urea, it is urease negative. C. pseudotuberculosis and C. ulcerans, on the other hand, are urease positive.
5. Nitrate Reduction Test
Positive Nitrate is converted to nitrite by C. diphtheriae. Since C. diphtheriae can convert nitrate to nitrite, it is typically positive for nitrate reduction.
6. Fermentation Test
These assays evaluate the bacteria’s capacity to ferment various carbohydrates. Generally, C. diphtheriae ferments both glucose and maltose.
Glucose: Produces acid during fermentation.
Maltose: Fermented, producing acid.
Sucrose: Depending on the strain, not always fermented.
Lactose: Not meant to ferment.
7. Cystinase Test
Positive. This assay determines if the substance has the capacity to hydrolyze cystine by creating a black stain on cystine tellurite agar.
8. Elek Test
Used to assess if diphtheria toxin is present, or how toxic the material is. Agar is used to embed a filter paper strip that has been impregnated with diphtheria antitoxin. Suspected C. diphtheriae is then streaked perpendicular to the strip. When a poison and an antitoxin are produced, a precipitation line is formed where they collide.
9. Gelatin Liquefaction
In the negative. Gelatin is not liquefied by C. diphtheriae.
10. Pyrazinamidase Test
Positive Pyrazinamidase is an enzyme produced by C. diphtheriae. Pyrazinamidase negative is a characteristic shared by all potentially toxic Corynebacterium species, including C. ulcerans, C. diphtheriae, and C. pseudotuberculosis. This indicates that they are deficient in pyrazinamidase, an enzyme that degrades the antibiotic pyrazinamide.
11. Starch Hydrolysis
In the negative. Starch is not hydrolyzed by C. diphtheriae.
It’s important to note that:
- To establish the presence of C. diphtheriae, these tests are utilized in concert with additional identifying techniques such colony morphology and Gram staining.
- The particular tests carried out could change based on the laboratory and regional guidelines.
- The toxigenicity test, which ascertains if the isolated C. diphtheriae strain generates the diphtheria toxin, is the most important stage in the diagnosis of diphtheria.
Conclusion
The presumed identification of C. diphtheriae in clinical specimens is aided by these biochemical tests. Nevertheless, further molecular techniques, like PCR for the identification of the diphtheria toxin gene (tox), are frequently needed for confirmation.
Frequently Asked Question(FAQ)
What lab tests for Corynebacterium diphtheriae?
The confirmation of toxigenic C diphtheriae in throat or lesion cultures by bacteriologic laboratory testing is necessary for the clinical diagnosis of diphtheria. Different types of media, such as Mueller-Miller tellurite agar, Tinsdale tellurite agar, or Loeffler agar, can be used for initial isolation.
Is Corynebacterium diphtheriae urease positive or negative?
diphtheriae by their cellular morphology and urease production (C. diphtheriae is urease negative).
What is the shape of Corynebacterium?
Gram-positive, club-shaped bacilli that belong to the Actinobacteria are called corynebacteria. Numerous corynebacteria can be found in the environment [27], on human skin, and on the skins of other mammals [28, 29].
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