VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

STAINING AND CULTURAL CHARACTERS

Staining

• Bacillus anthracis is an aerobic sporulating, Gram-positive rod.
• Inside the host’s body, it forms capsule, which can be demonstrated by Giemsa, or polychrome methylene blue stains in which capsule appear pale pink and bacillary body in blue.This phenomenon is called as MacFadyean reaction.
• In organ smears, the bacillus appears either single or in short chains of between 2 and 5 cells.
• Their ends are convex where they meet another individual. This causes the threads to assume the so-called bamboo stick form.
• Long chains of bacilli without capsules are formed in cultures.
• Spores develop only in the presence of O_z at temperature 25 -30°C.

Cultural characters

• Anthrax bacilli will grow on ordinary solid media after 48 hours at 37°C and form dull – surface colonies of moderate size and greyish – white (frosted glass) appearance.
• Under low magnification, the colonies are seen to have curved, twisted processes radiating from thin borders, which resemble locks of hair or plaits and give the appearance of a Medusa head or a woman’s curly hair or Judge's wig.
• No hemolysis is produced on blood agar in contrast to anthracoids.
• In gelatin stab cultures it produces Inverted fir tree type of growth. Liquefaction of the gelatin medium is slow.
• In the media containing serum, blood and incubated under CO₂ tension produces capsulated organisms and colonies are mucoid.

Biochemical properties of Bacillus anthracis

• Production of acid (but not gas)

Glucose	+
Maltose	+
Sucrose	+
Trehalose	+
Dextrin	+
Catalase	+
Indole	-
Methylene blue reduction	+
VP	+
Nitrates reduced to Nitrites	+
On egg yolk agar it produces lecithinase reaction	±

Laboratory Indications of Bacillus anthracis

• Nonhemolytic (sheep blood agar)
• Non-motile
• Gelatin hydrolysis Slow
• Catalase +