Difference between revisions of "Bacillus species"

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#REDIRECT[[:Category:Bacillus species]]
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<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
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<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
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 +
 
 +
===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 outgrowth sfrom 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''===
 +
 
 +
*Epidemiology:
 +
**Saprophyte in soil
 +
**Endospore formation allows persistence and spread
 +
**Endospores survive decades in the soil
 +
**Outbreaks in herbivores grazing pastures contaminated by spores from buried carcases
 +
**Infection usually by ingestion of spores and penetration through damaged mucosa
 +
*Pathogenesis and pathogenicity:
 +
**Spores germinate at site of entry and spread via lymphatics to bloodstream, where they multiply and produce toxin
 +
**Capsule and toxin (encoded by separate plasmids) required for virulence
 +
**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 antigen and lethal factor
 +
**Oedema factor is an adenylate cyclase which increases intracellular cAMP concetrations, causing fluid accumulation and damaging neutrophils
 +
**Lethal factor causes release of cytokines from macrophages
 +
**Protective antigen binds to the cell receptor to allow action of the other factors
 +
**The toxin kills phagocytes, increases capillary permeability and interferes with clotting cascade
 +
**Capillary thrombosis; leakage of fluid through damaged capillary endothelium
 +
**Systemic shock from circulatory collapse, [[General Pathology - Haemostasis#Haemorrhagic Disease Due To Vascular Fragility|haemorrhagic disease]] and oedema lead to death of the animal
 +
**Severe systemic disease that can result in [[Intestines - Fibrinous/ Haemorrhagic Enteritis#Bacterial septicaemia and enteritis|enteritis]]
 +
**Causes tissues to darken and swell due to oedema and necrosis
 +
*Clinical signs:
 +
**Cattle/sheep:
 +
***Fatal peracute septicaemia
 +
***Animals usually found dead
 +
***Pyrexia, depression, congested mucous membranes and petechiae before death
 +
***Abortion, subcutaneous oedema and dysentry in animals surviving more that one day
 +
**Pigs:
 +
***Subacute anthrax with oedematous swelling of throat, head and regional lymph nodes
 +
***Intestinal form with high mortality - dysentry due to haemorrhagic enteric lesions
 +
***[[Peritoneal cavity - inflammatory#In pigs|Peritonitis]]
 +
**Horses:
 +
***Subacute anthrax with subcutaneous oedema of thorax, abdomen and legs following entrance of spores into abrasions
 +
***Septicaemia with colic and dysentry due to haemorrhagic enteritis from ingestion of spores; ecchymoses and splenomegaly
 +
**Dogs
 +
***Rarely affected, but similar disease to that foung in pigs
 +
**Humans
 +
***Cutaneous anthrax - localised lesion from entrance into abrasion which can cause septicaemia
 +
***Pulmonary anthrax - inhalation of spores
 +
***Intestinal anthrax - ingestion of infective material
 +
*Diagnosis:
 +
**Post mortem: bloat, incomplete rigor mortis, ecchymoses, oedema, dark unclotted blood from orifices, blooy fluid in body cavities, splenomegaly
 +
**Blood smear from an ear or tail vein of ruminants, or peritoneal fluid from pigs stained with polychrome methylene blue
 +
**Chains of square-ended blue rods surrounded by mauve capsules
 +
**Culture on blood and MacConkey agar (no growth on MacConkey)
 +
**Biochemical tests
 +
*Treatment:
 +
**High doses of penicillin G or oxytetracylcine
 +
*Control:
 +
**Report suspected cases - notifiable
 +
**Spores destroyed by sterilisation
 +
**Endemic regions:
 +
***Live Sterne spore vaccine which produces toxin but has no capsule, therefore is non-pathogenic; stimulates protective antibody
 +
***Chemoprophylaxis with long-acting penicillin
 +
**Non-endemic regions after an outbreak:
 +
***Movement restrictions
 +
***Footbath with sporicidal disinfectant
 +
***Fumigate buildings with formaldehyde
 +
***Dispose carcases and contaminated material
 +
***Isolate in-contact animals
 +
 
 +
 
 +
===''Bacillus licheniformis''===
 +
 
 +
*Widespread in the environment
 +
*Associated with food spoilage
 +
*Abortion in cattle and sheep, possibly from spoiled silage or hay
 +
 
 +
 
 +
===''Bacillus cereus''===
 +
 
 +
*Mastitis in cattle
 +
*Food poisoning and eye infections in humans
 +
 
 +
 
 +
*''CAR bacillus'' in [[Respiratory Bacterial Infections - Pathology#CAR bacillus|URT infection in cattle]] and [[Respiratory Bacterial Infections - Pathology#In Rabbits|URT infection in rabbits]]

Revision as of 16:44, 31 July 2008

BACK TO INFECTIOUS AGENTS AND PARASITES
BACK TO BACTERIA


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 outgrowth sfrom 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

  • Epidemiology:
    • Saprophyte in soil
    • Endospore formation allows persistence and spread
    • Endospores survive decades in the soil
    • Outbreaks in herbivores grazing pastures contaminated by spores from buried carcases
    • Infection usually by ingestion of spores and penetration through damaged mucosa
  • Pathogenesis and pathogenicity:
    • Spores germinate at site of entry and spread via lymphatics to bloodstream, where they multiply and produce toxin
    • Capsule and toxin (encoded by separate plasmids) required for virulence
    • 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 antigen and lethal factor
    • Oedema factor is an adenylate cyclase which increases intracellular cAMP concetrations, causing fluid accumulation and damaging neutrophils
    • Lethal factor causes release of cytokines from macrophages
    • Protective antigen binds to the cell receptor to allow action of the other factors
    • The toxin kills phagocytes, increases capillary permeability and interferes with clotting cascade
    • Capillary thrombosis; leakage of fluid through damaged capillary endothelium
    • Systemic shock from circulatory collapse, haemorrhagic disease and oedema lead to death of the animal
    • Severe systemic disease that can result in enteritis
    • Causes tissues to darken and swell due to oedema and necrosis
  • Clinical signs:
    • Cattle/sheep:
      • Fatal peracute septicaemia
      • Animals usually found dead
      • Pyrexia, depression, congested mucous membranes and petechiae before death
      • Abortion, subcutaneous oedema and dysentry in animals surviving more that one day
    • Pigs:
      • Subacute anthrax with oedematous swelling of throat, head and regional lymph nodes
      • Intestinal form with high mortality - dysentry due to haemorrhagic enteric lesions
      • Peritonitis
    • Horses:
      • Subacute anthrax with subcutaneous oedema of thorax, abdomen and legs following entrance of spores into abrasions
      • Septicaemia with colic and dysentry due to haemorrhagic enteritis from ingestion of spores; ecchymoses and splenomegaly
    • Dogs
      • Rarely affected, but similar disease to that foung in pigs
    • Humans
      • Cutaneous anthrax - localised lesion from entrance into abrasion which can cause septicaemia
      • Pulmonary anthrax - inhalation of spores
      • Intestinal anthrax - ingestion of infective material
  • Diagnosis:
    • Post mortem: bloat, incomplete rigor mortis, ecchymoses, oedema, dark unclotted blood from orifices, blooy fluid in body cavities, splenomegaly
    • Blood smear from an ear or tail vein of ruminants, or peritoneal fluid from pigs stained with polychrome methylene blue
    • Chains of square-ended blue rods surrounded by mauve capsules
    • Culture on blood and MacConkey agar (no growth on MacConkey)
    • Biochemical tests
  • Treatment:
    • High doses of penicillin G or oxytetracylcine
  • Control:
    • Report suspected cases - notifiable
    • Spores destroyed by sterilisation
    • Endemic regions:
      • Live Sterne spore vaccine which produces toxin but has no capsule, therefore is non-pathogenic; stimulates protective antibody
      • Chemoprophylaxis with long-acting penicillin
    • Non-endemic regions after an outbreak:
      • Movement restrictions
      • Footbath with sporicidal disinfectant
      • Fumigate buildings with formaldehyde
      • Dispose carcases and contaminated material
      • Isolate in-contact animals


Bacillus licheniformis

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


Bacillus cereus

  • Mastitis in cattle
  • Food poisoning and eye infections in humans


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