Bacteria Genomes - CORYNEBACTERIUM DIPTHERIAE

Corynebacterium diphtheriae is a Gram-positive , non-spore forming, non-motile, pleomorphic rod belonging to the genus Corynebacterium and the actinomycete group of organisms. The organism produces a potent bacteriophage-encoded protein exotoxin, diphtheria toxin (DT), which causes the symptoms of diphtheria.

There are three biotypes - gravis, intermedius, and mitis. The most severe disease is associated with the gravis biotype, but any strain may produce toxin.

Diptheria is a potentially fatal infectious disease but has been controlled in many developed countries by an effective immunisation programme. However, the disease has made a dramatic return in recent years, in particular within the Eastern European region. The largest, and still on-going, outbreak since the advent of mass immunisation started within Russia and the newly independent states of the former Soviet Union in the 1990s.

Hippocrates first described the disease in the 5th Century B.C. The name of the disease is derived from the Greek diphthera, meaning leather hide. Diptheria epidemics were described in the 6th Century A.D. by Aetius and the bacterium was first observed in diphtheritic membranes by Klebs in 1883 and cultivated by Lffler in 1884. Antitoxin was invented in late 19th century, and toxoid was developed in the 1920s.

The incubation period of diphtheria is 2-5 days (range, 1-10 days) and susceptible persons may acquire toxigenic diphtheria bacilli in the nasopharynx, the onset is indistinguishable from that of the common cold and is usually characterised by a mucopurulent nasal discharge (containing both mucus and pus) which may become blood-tinged. Most complications of diphtheria, including death, are attributable to effects of the toxin produced at the site of the membrane which is absorbed into the bloodstream and then distributed to the tissues of the body. The toxin is responsible for the major complications of myocarditis and neuritis and can also cause low platelet counts (thrombocytopenia) and protein in the urine (proteinuria). Clinical disease associated with non-toxin-producing strains is generally milder.

Research has provided evidence that recent acquisition of pathogenicity factors goes beyond the toxin itself, and includes iron-uptake systems, adhesins and fimbrial proteins. This is in contrast to Corynebacterium 's nearest sequenced pathogenic relative, Mycobacterium tuberculosis , where there is little evidence of recent horizontal DNA acquisition.

References:

Nucleic Acids Res. 31 (22):6516-23 (2003)
http://www.sanger.ac.uk/Projects/C_diphtheriae/
http://www.tjclarkinc.com/bacterial_diseases/diphtheria_.htm
J. Clin. Microbiol. 3(5):1080-3 (1995)