|Bacillus anthracis - colonies on nutrient agar and
cotton-like rising deposit in liquid medium
Phylum Firmicutes, Class Bacilli, Order Bacillales, Family Bacillaceae, Genus Bacillus, Bacillus anthracis Cohn 1872
Old synonym: B. cereus var. anthracis Smith, Gordon and Clark,1946; Bacteridium anthracis (Cohn) Hauduroy et al. 1953.
Closely related to Bacillus cereus.
Can be distinguished from other members of the Bacillus cereus group by AFLP
(amplified fragment length polymorphism) analysis; Ba813 DNA sequence (277 bp)
is specific chromosomal marker for B. anthracis and in combination with sequencing
of parts of lef and cap genes its sequence allows the identification of virulent strains.
Gram-positive rods, straight, large, 3-6 / 1-1.25 μm, nonmotile (noncilliated bacilli),
forming chains or filaments. Ellipsoidal, non-deforming spore located central or para-
central . Nonmotile. Capsulate. Capsule is produced ‘in vivo’ or in blood containing
medium (or medium with ascitic liquid). The capsule can be visualized by staining
smears with M’Fadyean’s polychrome methylene blue or India ink.
Aerobic, facultative anaerobic. Grows easily on simple media. Growth temperature
range 15-40 ºC. NaCl is not required for growth. In liquid medium produce low
turbidity and cotton-like agglutination.
Colonies on agar are large, 6-7 mm diameter, opaque, non-pigmented, circular to
irregular with entire to undulate, crenate and fimbriate edges, and granular surface
textures. Nonhemolytic. Colonies of the capsulate strains appear mucoid.
Soil inhabitant in sporulated form. Isolated from blood of animals and humans with
anthrax, animal carcasses and products and soil contamined with spores.
Usually susceptible to penicillin, streptomycin, tetracyclines, doxycycline, gentamicin,
chloramphenicol and erythromycin. Susceptible to gamma phage. Resistant to many
cephalosporins. Growth with lysozyme is present.
Pathogenicity factors: capsule, enzymes (lecithinase, proteases, colagenase), toxins.
Virulence genes are carried by plasmids pX01 (toxins) and pX02 (capsule); these
plasmids may be transmissible to other members of the B. cereus group.
Causes anthrax (septicaemia) to all mammalians (mainly herbivores), rarely to birds.
Anthrax carcasses can remain infectious for many years, even when buried with
In humans, pathogenic strains can produce skin infection (black – anthrakitis gr.) or
intestinal, pulmonary, meningeal infections. Non-virulent strains can produce
bacteremia. Bacillus anthracis has long been considered a potential agent for
biological warfare or bioterrorism.
Experimental infection on mice, rats, rabbits, hamsters, chimps.
The cell-wall polysaccharide antigen may be masked in vivo by the organism’s poly-
gamma-D-glutamic acid capsule.
Bacillus anthracis spore surface antigens were found to crossreact with spores of
several other Bacillus species.
- Bîlbîie V., Pozsgi N., 1985, Bacteriologie Medicală, vol.ll, Ed. Medicală, Bucureşti.
- Gordon R.E., Haynes W.C., Pang C.H. (1973) – The genus Bacillus. Agriculture Handbook No. 427, U.S.D.A., Washington D.C.
- Buchanan R.E., Gibbons N.E., Cowan S.T., Holt J.G., Liston J., Murray R.G.E., Niven C.F., Ravin A.W., Stanier R.W. (1974) - Bergey’s
Manual of Determinative Bacteriology, Eight Edition, The Williams & Wilkins Company, Baltimore.
- Buiuc D., Negut M. , 2009. Tratat de Microbiologie Clinica, editia a III-a, Editura Medicala, Bucuresti.
- N.A. Logan and P. De Vos, 2009. Genus I. Bacillus Cohn 1872. In: (Eds.) P.D. Vos, G. Garrity, D. Jones, N.R. Krieg, W. Ludwig, F.A.
Rainey, K.-H. Schleifer, W.B. Whitman. Bergey’s Manual of Systematic Bacteriology, Volume 3: The Firmicutes, Springer, 21-127.
Positive results for nitrate reduction, Voges-Proskauer reaction, decomposition of
gelatin (slowly), casein hydrolysis, starch hydrolysis, catalase, egg-yolk reaction, acid
production from glucose, glycogen, maltose, N-acetyl-D-glucosamine, ribose, starch,
sucrose and trehalose.
Negative results for arginine dihydrolase, indole production, degradation of tyrosine,
beta-galactosidase, lysine decarboxylase, ornithine decarboxylase, oxidase, urease,
acid production from: arabinose, adonitol, amygdalin, D- and L-arabitol, cellobiose,
dulcitol, erythritol, D- and L-fucose, galactose, beta-gentibiose, gluconate, glycerol,
meso-inositol, 2- and 5-ketogluconate, lactose, lyxose, mannitol, D-mannose,
melezitose, melibiose, methyl beta-mannoside, methyl beta-xyloside, raffinose,
rhamnose, salicin, sorbitol, sorbose, tagatose, turanose, xylitol, D- and L-xylose.
Variable results for citrate utilization (depending on method used), alkaline digestion
of litmus milk, acid production from arbutin and fructose.
(c) Costin Stoica
|Malachite-green-stained, central, non-deforming
spores (Bacillus anthracis)
|Close-up image of Bacillus anthracis colonies on
sheep blood agar