Anthrax causes
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Anthrax Microchapters |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Taxonomy
Bacteria; Archaebacteria; Firmicutes; Bacilli; Bacillales; Bacillaceae; Bacillus; anthracis; Bacillus anthracis
Biology
B. anthracis, the causative agent of anthrax, is a Gram-positive, aerobic or facultatively anaerobic, endospore-forming, rod-shaped bacterium approxi- mately 4 μm by 1 μm, although under the micro- scope it frequently appears in chains of cells. in blood smears, smears of tissues or lesion fluid from diagnostic specimens, these chains are two to a few cells in length; in smears made from in vitro cultures, they can appear as endless strings of cells – responsible for the characteristic tackiness of the colonies and for the flocculating nature of broth cultures. Also characteristic is the square-ended (“box-car” shaped) appearance traditionally associated with B. anthracis vegetative cells, although this may not always be very clear. In the presence of oxygen, and towards the end of the exponential phase of growth, one ellipsoidal spore (approximately 2 μm by 1 μm in size) is formed in each cell; this does not swell the sporangium and is generally situated centrally, sometimes sub terminally.
In the absence of oxygen and under a high partial pressure of Co2 in the presence of bicarbonate (hCo3-), the vegetative cell secretes its polypeptide capsule and it is one of the two established in vivo virulence factors of B. anthracis. The capsule is also a primary diagnostic aid.