Bacillus species

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Bacillus anthracis

Overview

  • Mostly non-pathogenic environmental organisms
  • Bacillus anthracis causes anthrax
  • Bacillus licheniformis may cause shoradic abortions in cattle and sheep
  • Bacillus cereus causes food poisoning in humans and mastitis in cows


Characteristics

  • Large, Gram positive rods
  • Produce endospores
  • Aerobes or facultative anaerobes
  • Grow on non-enriched media
  • Motile
  • Catalase positive, oxidase negative
  • Bacillus anthracis colonies are up to 5mm diameter, flat, dry, grey, with a ground-glass appearance; curled outgrowthsfrom the edge of the colony give a 'medusa head' appearance; non-haemolytic (differentiate from Bacillus cereus)
  • Bacillus licheniformis forms dull, rough, wrinkled colonies, with hair-like outgrowths
  • Biochemical tests for identification
  • Can often tolerate adverse environmental conditions


Bacillus anthracis

  • Saprophyte in soil
  • Capsule composed of homopolymer of D-isomer of glutamic acid allows survival in the body by resisting phagocytosis
  • Capsule stains mauve with polychrome methylene blue in the MacFadyean's reaction - identify anthrax in blood samples
  • Bacilli appear as chains of dark blue, square-ended rods surounded with the capsule
  • Extracellular toxin (holotoxin) composed of oedema factor, protective factor and lethal factor


Bacillus licheniformis

  • Widespread in the environment
  • Associated with food spoilage
  • Abortion in cattle and sheep, possibly from spoiled silage or hay