Bacillus anthracis
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 Photomicrograph of Bacillus anthracis (fuchsin-methylene blue spore stain).
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| Bacillus anthracis Cohn 1872 |
Bacillus anthracis is a Gram-positive, facultatively anaerobic, rod-shaped bacterium of the genus Bacillus. An endospore forming bacterium, B. anthracis is a natural soil-dwelling organism, as well as the causative agent of anthrax.[1]
Each cell is about 1 by 6 μm in size.
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[edit] Historical background
Casimir Davaine found the bacteria in sick people [2]. B. anthracis was the first bacterium conclusively demonstrated to cause disease, by Robert Koch in 1877.[3] The species name anthracis is from the Greek anthrakis (ἄνθραξ), meaning coal and referring to the most common form of the disease, cutaneous anthrax, in which large black skin lesions are formed.
When cutaneous anthrax affects a patient a painless, raised nodule forms at the site. As the B. anthracis continues to grow, the cells surrounding the nodule die and the nodule spreads. Eschar, the name given to the enlarged blackened (from the dead cells) lesion comes from a Greek word meaning "charcoal."
[edit] Pathogenicity
Under conditions of environmental stress, B. anthracis bacteria naturally produce endospores which rest in the soil and can survive for decades in this state. B. anthracis may be inoculated into a wound, inhaled or ingested. In ruminants, the bacterium causes sudden death from septicaemia. For this reason any ruminants found to have died suddenly and without obvious reason should be treated as a suspected anthrax case. In these event, a blood sample is taken, by a qualified veterinary surgeon, from a superficial vein and subjected to the MacFaydean polychrome methylene blue staining procedure which screens for B.anthracis. Confirmational diagnosis is achieved through PCR and Immunofluorescence.
Horses respond variably to B.anthracis depending on the site of entry. Ingestion tends to lead to a severe enteritis and septicaemia. Inoculation in the skin tends to result in a local swelling and associated lymphadenitis. In pigs, B. anthracis again causes an acute necrotising tonsillitis, or a subacute pharyngeal swelling, or the intestinal disease described in horses. The intestinal disease carries a higher mortality. Dogs and cats seem less susceptible to B.anthracis and require a relative large dose of infectious agent before they begin to show clinical signs.
B. anthracis has at least 89 known strains, ranging from highly virulent strains with biological warfare and bioterrorism applications (Ames and Vollum) to benign strains used for inoculations (Sterne). The strains differ in presence and activity of various genes, determining their virulence and production of antigens and toxins. The form associated with the 2001 anthrax attacks produced both toxin (consisting of three proteins: the protective antigen, the edema factor and the lethal factor) and a capsule (consisting of a polymer of glutamic acid). Infection with anthrax requires the presence of all three of these exotoxins.[4]
The bacterium can be cultivated in ordinary nutrient medium under aerobic or anaerobic conditions.
[edit] Treatment
Infections with B. anthracis can be treated with β-lactam antibiotics such as penicillin, and others which are active against Gram-positive bacteria.[5]
[edit] External links
[edit] References
- ^ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9.
- ^ Théodoridès, J (Apr 1966). Casimir Davaine (1812-1882): a precursor of Pasteur. Medical history 10 (2): 155-65. PMID 5325873.
- ^ Madigan M, Martinko J (editors). (2005). Brock Biology of Microorganisms, 11th ed., Prentice Hall. ISBN 0-13-144329-1.
- ^ Dixon TC, Meselson M, Guillemin J, Hanna PC (1999). "Anthrax". N. Engl. J. Med. 341 (11): 815-26. doi:. PMID 10477781.
- ^ Barnes JM (1947). "Penicillin and B. anthracis.". J Path Bacteriol 194: 113.
