Corynebacterium diphtheriae
A Microbial Biorealm page on the genus Corynebacterium diphtheriae
Classification
Higher order taxa
Species
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NCBI: Taxonomy |
Corynebacterium diphtheriae
Description and significance
- Picture from textbookofbacteria.net to be included hopefully
- Note - include picture of Emil Von Behring
C. diphtheriae is a gram-positive, aerobic, nonmotile, toxin-producing, rod-shaped bacteria belonging to the order Actinomycetales, which are typically found in soil, but also have pathogenic members such as streptomyces and mycobacteria. C. diphtheriae is best known for causing the disease Diphtheria in human begins, which results from production of Diphtheria toxin in conjunction with infection by a bacteriophage which provides it with the toxin-producing gene. Because historically it has been a very deadly disease, especially for children where mortality rates before vaccines and antitoxin amounted to nearly 80%, it has been heavily studied. Oddly enough, mice and other rodents are naturally immune to the Diphtheria toxin so it has been difficult to study Diphtheria in the lab.
Diseases resembling Diphtheria were described as early as the 4th Century BCE by Hippocrates. It was named in 1826 by French physician Pierre Bretonneau, who gave it the name Diphtheria from the Greek word which means "leather hide". It was named "leather hide" because of the leathery layer that grows on the tonsils, throat, and nasal passages. Corynebacterium diphtheriae was first described in 1884 by Edwin Klebs and Friedrich Loffler, giving it the name Klebs-Loffler bacillus by which it used to be known.
In 1888, Emile Roux discovered that a toxin produced by C. diphtheriae was the causative agent in the disease Diphtheria. Emil Von Behring (1854-1917) was one of the first pioneers in the race to fight Diphtheria. He studied C. diphtheriae from 1889 onwards, especially in animals. When he discovered that the serum of anthrax-resistant rats was able to kill the anthrax bacillus, he researched such possibilities for Diphtheria, eventually using the serum of Diphtheria toxin-resistant guinea pigs, and ultimately horses. Eventually he developed antiserum, based on his experiments, as well as theories developed by a previous colleague Shibasaburo Kitasato. By 1892, the antiserum was ready for commercial production. In 1891, Behring was awarded the Nobel Prize in Medicine for his work.
In 1923, the work of Alexander Glenny, Barbara Hopkins, and Gaston Ramon produced a vaccine for Diphtheria. Glenny and Hopkins found that formaldehyde could prevent the Diphtheria toxin from being toxic, while Ramon discovered that the nontoxic form still retained its antigenic qualities. The form of the toxin which results from denaturing with formaldehyde is called an anatoxin, "toxoids", or "formalin-toxoids", and is used in vaccinations worldwide.
- Will include a picture of Balto
Outbreaks of Diptheria were common earlier in the 18th and 19th century, but the introduction of the vaccine caused a temporary decline in the number of cases. One of the more well-known outbreaks of Diphtheria was commemorated in the animated film "Balto", a story about the dog sled team (whose lead dog was named Balto) which brought the Diphtheria antiserum from Nenana to Nome, which was geographically isolated during the epidemic. They traveled 700 miles in 6 days through temperatures of minus 40 degrees Celsius and blizzard-speed winds. The dog sled team saved hundreds of lives, the story was sensationalized worldwide, and a statue of Balto, the lead dog, was erected in New York's Central Park.
Despite having a vaccine and antiserum, there is currently an increase in the number of cases in the United States and many countries in eastern Europe. Research is being done to determine why new epidemics are being seen - whether it is a result of a mutation in C. diphtheriae, or if it is from environmental and social factors such as poor immunization rates and unsanitary conditions.
Genome structure
Image from Wishart Research Group, University of Alberta
The genome of C. diphtheriae contains 2,488,635 nucleotides, 87% of which are coding. This single circular chromosome contains 2,389 genes from which 2,272 proteins are coded. It contains no plasmids. There are 69 structural RNA, 15 coding for 5S, 23S, and 16S Ribosomal RNA, and 54 coding for the 20 amino acid tRNA molecules. The GC content is 53%, though it is not evenly distributed - it has higher proportion of GC pairs near the origin of the plasmid (around 55%), compared to the region near the terminus (49%)
The genome contains what are termed Pathogenicity Islands (PAIs). These PAIs, of which C. diphtheriae has 13, contain local genetic anomalies in nucleotide composition or frequency, and many are closely associated with patches that code for tRNA. These PAIs code for the majority of fimbrial and fimbria-related genes, and iron-uptake systems which produce siderophores and lantibiotics. The ability to acquire iron allows C. diphtheriae to produce the Diphtheria toxin, which gives the bacteria its pathogenicity.
Cell structure and metabolism
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Ecology
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Pathology
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Application to Biotechnology
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Current Research
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References
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Edited by student Rachael Spradley of Rachel Larsen
