Bacillus anthracis

Bacillus anthracis
	Photomicrograph of Bacillus anthracis (fuchsin-methylene blue spore stain).; Photomicrograph of Bacillus anthracis (fuchsin-methylene blue spore stain).
Scientific classification
Kingdom:	Bacteria;
Phylum:	Firmicutes;
Class:	Bacilli;
Order:	Bacillales;
Family:	Bacillaceae;
Genus:	Bacillus;
Species:	B. anthracis;
Binomial name
	Bacillus anthracis; Cohn 1872

File:B anthracis diagram en.png

Structure of Bacillus anthracis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Jesus Rosario Hernandez, M.D. [2]

Overview

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.

Historical background

B. anthracis was the first bacterium conclusively demonstrated to cause disease, by Robert Koch in 1877.^[2] 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.

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. When ingested by a cattle, sheep, or other herbivores, the bacteria begin to reproduce inside the animal and eventually kill it, then continue to reproduce in its carcass. Once the nutrients are exhausted, new endospores are produced and the cycle repeats.^[3]

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.

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]

References

↑ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0-8385-8529-9.
↑ Madigan M, Martinko J (editors). (2005). Brock Biology of Microorganisms (11th ed. ed.). Prentice Hall. ISBN 0-13-144329-1.CS1 maint: Extra text (link)
↑ Turnbull PCB (1996). Bacillus. In: Barron's Medical Microbiology (Baron S et al, eds.) (4th ed. ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1.CS1 maint: Extra text (link)
↑ Dixon TC, Meselson M, Guillemin J, Hanna PC (1999). "Anthrax". N. Engl. J. Med. 341 (11): 815–26. PMID 10477781.
↑ Barnes JM (1947). "Penicillin and B. anthracis". J Path Bacteriol. 194: 113.