This MedLibrary.org supplementary page on Corynebacterium diphtheriae is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
| Corynebacterium diphtheriae | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
 Gram stained Corynebacterium diphtheriae culture
|
||||||||||||
| Scientific classification | ||||||||||||
|
||||||||||||
| Binomial name | ||||||||||||
| Corynebacterium diphtheriae Kruse, 1886 |
Corynebacterium diphtheriae is a pathogenic bacterium that causes diphtheria. It is also known as the Klebs-Löffler bacillus, because it was discovered in 1884 by German bacteriologists Edwin Klebs (1834 – 1912) and Friedrich Löffler (1852 – 1915).
Contents |
Morphology and toxin production
C. diphtheriae is a aerobic organism [1] Gram positive organism, characterized by non-encapsulated, non-sporulated, immobile, straight or curved rods with a length of 1 to 8 µm and width of 0.3 to 0.8 µm, which form ramified aggregations in culture (looking like "Chinese characters")and sometimes which have clubbed ends[Gr.Coryne,a club] . The bacterium may contain polymetaphosphate aggregates called Volutin granules. It is pathogenic only in humans. C. diphtheriae produce diphtheria toxin, a proteic exotoxin, with a molecular weight of 62 kilodaltons which ADP-ribosylates host EF-2, resulting in the inhibition of protein synthesis and thus is responsible for the signs of diphtheria. The inactivation of this toxin with an antitoxic serum (antitoxin) is the basis of the antidiphtheric therapeutic vaccination. However, not all strains are toxigenic; the ability to produce the exotoxin is conferred on the bacterium when it is infected by a bacteriophage (a mechanism termed "lysogenic activation"). A non-toxigenic strain can thus become toxigenic by the infection of such a bacteriophage.
Classification
Four subspecies are recognized: C. diphtheriae mitischodis, C. diphtheriae intermedius, C. diphtheriae gravis, and C. diphtheriae belfanti. The four subspecies differ slightly in their colonial morphology and biochemical properties such as the ability to metabolize certain nutrients, but all may be toxigenic (and therefore cause diphtheria) or non-toxigenic.
Diagnosis
In order to accurately identify C. diphtheriae, a Gram stain is performed to show gram-positive, highly pleomorphic organisms with no particular arrangement (classically resembling Chinese characters). Then, culture the organism on an enrichment medium, namely Löffler's serum, to allow it to overgrow any other organisms present in the specimen. After that, use a selective plate known as tellurite agar which allows all Corynebacteria (including C. diphtheriae) to reduce tellurite to metallic tellurium producing brown colonies and, only in the case of C. diphtheriae, a black halo around the colonies allowing for easy differentation of the organism.
A low concentration of iron is required in the medium for toxin production. At high iron concentrations, iron molecules bind to an aporepressor on the beta bacteriophage which carries the genes for the Tox gene, converting it to a repressor which shuts down toxin production[2]. This is most appreciated when performing Elek's test for toxogenecity, in order to know if the organism is able to produce the diphtheria toxin or not.
Sensitivity
The bacterium is sensitive to the majority of antibiotics, such as the penicillins, ampicillin, cephalosporins, quinolones, chloramphenicol, tetracyclines, cefuroxime and trimethoprim.
References
- ^ Corynebacterium diphtheriae - Material Safety Data Sheets (MSDS)
- ^ Microbiology: A Human Perspective. Fourth edition. McGraw Hill
External links
- CoryneRegNet - Database of Corynebacterial Transcription Factors and Regulatory Networks
Wikipedia content modification information:
- This page was last modified on 28 September 2008, at 04:37.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Corynebacterium diphtheriae".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.