Morphology

MORPHOLOGY

  • Members of the family are Gram +ve large rods, aerobic (facultative anaerobic), endospore forming, capsulated, mostly catalase positive and fermentative organisms. They are motile by peritrichous flagella.
  • The anthrax bacillus is one of the largest pathogenic bacteria. They are Gram +ve, straight, rod shaped, non-motile organisms measuring 4-8 μm x 1-1.5 μm.
  • In cultures the bacilli are arranged end to end in long chains. The ends of the bacilli are truncated or often concave and somewhat swollen.
  • Chain of bacilli presents a bamboo stick appearance (and also called as Box –car bacillus - looks like linked rail carriages).
  • In tissues or in blood smear, it is found singly, in pairs or in short chains, the entire bacilli being surrounded by capsule.
  • The capsule is polypeptide in nature, being composed of a polymer of d-glutamic acid.
  • Capsules are not formed under ordinary conditions of culture, but only if the media contains serum, albumen, charcoal, starch or bicarbonates with reduced partial pressure of carbon dioxide.
  • When blood films containing bacilli are stained with polychrome methylene blue for a few seconds and examined under the microscope, an amorphous purplish material is noticed around the bacilli. This represents the capsular material and is characteristic of the anthrax bacilli. This is called asreaction. This reaction depends on the degree of heat employed for fixation of a blood film.

Mc Fadyean’s Reaction

  • Sporulation occurs readily outside the body in the presence of oxygen. Spores are formed in culture or in the soil, but never in the animal body during life.
  • Sporulation occurs under unfavourable conditions for growth and is encouraged by distilled water, 2% NaCl or growth in oxalated agar. Sporulation takes place at an optimum temperature of 25-30°C and in atmosphere containing low partial pressure of oxygen. Sporulation is inhibited by anaerobic conditions and by CaCl2
  • Spores are central, elliptical or oval in shape and are of the same width as the bacillary body. So that they do not cause bulging of the vegetative cell. The spores do not stain by ordinary methods. But can be stained with Sudan black B.
Last modified: Monday, 4 June 2012, 4:19 AM