Difference between revisions of "Bacillus species"

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*Mostly non-pathogenic environmental organisms
 
*Mostly non-pathogenic environmental organisms
 
*''Bacillus anthracis'' causes anthrax
 
*''Bacillus anthracis'' causes anthrax
 +
*Anthrax is a severe disease affecting all mammals worldwide
 +
*Ruminants are highly susceptible to anthrax, dying of a septicaemic form
 +
*Pigs and horses are moderately susceptible, but carnivores are fairly resistant
 
*''Bacillus licheniformis'' may cause shoradic abortions in cattle and sheep
 
*''Bacillus licheniformis'' may cause shoradic abortions in cattle and sheep
 
*''Bacillus cereus'' causes food poisoning in humans and mastitis in cows
 
*''Bacillus cereus'' causes food poisoning in humans and mastitis in cows
Line 31: Line 34:
 
===''Bacillus anthracis''===
 
===''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
 
 
*
 
*
 +
*Pathogenesis and pathogenicity:
 +
**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
 +
**Oedema factor is an adenylate cyclase which increases intracellular cAMP concetrations, damaging phagocytes
 +
**Protective factor binds to the cell receptor to allow action of the other factors
 +
**The toxin kills phagocytes, increases capillary permeability and interferes with clooting cascade
 +
**Capillary thrombosis; leakage of fluid through damaged capillary endothelium
 +
**Systemic shock from circulatory collapse, haemorrhage and oedema lead to death of the animal
 +
*Clinical signs:
 +
**
  
  

Revision as of 12:50, 17 May 2008

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Bacillus anthracis

Overview

  • Mostly non-pathogenic environmental organisms
  • Bacillus anthracis causes anthrax
  • Anthrax is a severe disease affecting all mammals worldwide
  • Ruminants are highly susceptible to anthrax, dying of a septicaemic form
  • Pigs and horses are moderately susceptible, but carnivores are fairly resistant
  • 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

  • Pathogenesis and pathogenicity:
    • 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
    • Oedema factor is an adenylate cyclase which increases intracellular cAMP concetrations, damaging phagocytes
    • Protective factor binds to the cell receptor to allow action of the other factors
    • The toxin kills phagocytes, increases capillary permeability and interferes with clooting cascade
    • Capillary thrombosis; leakage of fluid through damaged capillary endothelium
    • Systemic shock from circulatory collapse, haemorrhage and oedema lead to death of the animal
  • Clinical signs:


Bacillus licheniformis

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