Difference between revisions of "Clostridium species"

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*Large Gram-positive rods  
 
*Large Gram-positive rods  
*Obligate Anaerobes
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*Obligate anaerobes
 
*Fermentative, catalase negative, oxidase negative
 
*Fermentative, catalase negative, oxidase negative
 
*Straight or slightly curved
 
*Straight or slightly curved
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*Require enriched media for growth
 
*Require enriched media for growth
 
*Produce endospores which vary in shape and location and cause bulging of mother cell
 
*Produce endospores which vary in shape and location and cause bulging of mother cell
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===Pathogenesis and pathogenicity===
 
===Pathogenesis and pathogenicity===

Revision as of 16:24, 20 May 2008

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Overview

  • Organisms present in the soil, alimentary tract and faeces
  • Endospores may be present in liver and may be reactivated to cause disease
  • Neurotoxic clostridia, Clostridium tetani and Clostridium botulinum affect neuromuscular function but cause no tissue damage
  • Histotoxic clostridia cause localised lesions in tissues and may cause toxaemia
  • C. perfringens cause inflammatory lesions in the gastrointestinal tract and enterotoxaemias in sheep


Characteristics

  • Large Gram-positive rods
  • Obligate anaerobes
  • Fermentative, catalase negative, oxidase negative
  • Straight or slightly curved
  • Motile by flagellae
  • Require enriched media for growth
  • Produce endospores which vary in shape and location and cause bulging of mother cell


Pathogenesis and pathogenicity

  • Produce extracellular digestive enzymes and toxic substance known as exotoxins
  • Exotoxins cause necrosis, haemolysis and death
  • Collagenase, hyaluronidase and DNase enymes facilitate spread through tissues


Clostridium tetani

  • Causes tetanus
  • Acute, potentially fatal intoxication affecting many species
  • Horses and man particularly susceptible; carnivores fairly resistant
  • Found in horse faeces
  • Characteristics:
    • Terminal, spherical endospores give mother cells a drumstick appearance
    • Enodospores resistant to boiling and chemicals but susceptible to autoclaving
    • Swarming growth and haemolytic on blood agar
    • Many serotypes but all produce same neurotoxin, tetanospasmin, therefore antibodies neutralise all
  • Pathogenesis:
    • Endospores introduced via damaged tissues e.g. penetrating wounds
    • Damaged tissue creates an anaerobic environment, allowing germination of spores
    • Tetanospasmin made by bacteria replicating in damaged tissue
    • Absorbed toxin affects neuromuscular junction distant from site of toxin production
    • Neurotoxin binds irreversibly to ganglioside receptors on motor neurons and is transported to nerve cell body
    • Toxins transported across synapse to terminals of inhibitory neurons where they block transmission of signals
    • Spastic paralysis by constant tensing of muscles results
    • Toxin can be blood-borne and bind to motor terminals throughout the body as well as in the CNS
  • Clinical signs:
    • Incubation period 5-10 days
    • Stiffness, localised spasms, altered heart and respiratory rates, dysphagia, altered facial expression, lock-jaw from mastigatory muscle spasm
    • Tonic muscle contraction easily stimulated
  • Treatment:
    • Antitoxin IV or into subarachnoid space on 3 consecutive days
    • Toxoid subcutaneously to promote active immune response
    • Penicillin to kill vegetative cells
    • Debridement and flushing of wound with hydrogen peroxide
    • Fluids, sedatives, muscle relaxants
  • Control:
    • Toxoid vaccine for farm animals
    • Debridement of wounds in horses


Clostridium botulinum

  • Ubiquitous organism
  • Oval, subterminal endospores; spores survive boiling for hours
  • Causes botulism, a potentially fatal intoxication
  • Germination of endospores, growth of bacterial cells and toxin production in anaerobic conditions e.g. decaying carcasses and vegetation
  • Disease in animals consuming rotting carcasses and in herbivores through contamination of feed
  • Pathogenesis:
    • Intoxication on ingestion and absorbtion of toxin from GIT into the blood
    • Occasionally germination of spores in wounds or GIT
    • Neurotoxin carried to peripheral nervous system
    • Toxin binds gangliosides irreversibly at the neuromuscular junction
    • Blocks release of acetylcholine
  • Clinical signs:
    • Dilated pupils, dry mucus membranes, decreased salivation, tongue flacidity, dysphagia in farm animals
    • Incoordination and knuckling followed by flacid paralysis and recumbency
    • Paralysis of respiratory muscles leads to death
    • Flacid paralysis of legs and wings in birds
  • Diagnosis:
    • Mouse inoculation with infected serum
    • Toxin detection by PCR, ELISA
    • Toxin neutralisation tests in mice
  • Treatment: polyvalent antiserum neutralises unbound toxin
  • Toxoid vaccine used in endemic regions
  • Implicated in equine grass sickness


Histotoxic infections

  • Exotoxins cause local tissue necrosis and systemic effects which can be fatal - toxaemia
  • C. chauvei and C. septicum present in muscle as latent spores which can germinate to cause infection
  • C. novyi type B and C. haemolyticum have latent spores in the liver
  • When inoculated into wounds, cause malignant oedema and gas gangrene
  • Endospores persist in the soil
  • Most ingested spores excreted in faeces, but some become dormant in tissues
  • Tissue injury leads to reduced oxygen tensions allowing germination and replication of bacteria
  • Exotoxins cause local necrosis
  • Activated spores in the liver and muscles cause endogenous infections including blackleg, infectious necrotic hepatitis and bacillary haemoglobinuria
  • Inoculation of wounds causes exogenous infections including malignant oedema and gas gangrene


Clostridium chauvei

  • Black leg:
    • Acute disease of cattle and sheep
    • Endogenous infection in young cattle with latent spores in muscles, activated by trauma
    • Exogenous infection via wounds in sheep of any age
    • Gangrenous cellulitis and myositis caused by exotoxins leads to rapid death
    • Skeletal muscle damage with lameness, swelling and crepitus due to gas accumilation
    • Dyspnoea due to lesions in tongue and throat muscles
    • Myocardial and diaphragmatic lesions can cause sudden death
    • Fluorescent antibody test for diagnosis
  • Causes gas gangrene, along with Clostridium septicum


Clostridium septicum

  • Causes malignant oedema:
    • Infection via wounds
    • Cellutis with minimal gangrene and gas formation
    • Tissue swelling die to oedema; coldness and discoloration of overlying skin
    • Toxaemia with depression; death may be rapis if extensive lesions
  • Causes braxy:
    • Abomasitis of sheep
    • Disease occurs during winter
    • Rapidly fatal; anorexia, depression, fever
  • Causes gas gangrene and myositis


Clostridium perfringens


Clostridium novyi

  • Infectious necrotic hepatitis/black disease:
    • Acute disease of sheep, occasionally cattle
    • Hepatic necrosis caused by exotoxins of C. novyi type B in liver damaged by Fasciola hepatica
    • Rapid death
    • Dark discoloration of skin caused by subcutaneous venous congestion
    • Fluorescent antibody test diagnostic
  • Causes gas gangrene and myositis.
  • May be involved in cutaneous lesions
  • Causes big head in rams - oedema of subcutaneous tissues of the head, neck and cranial thorax; necrotising lethal alpha toxin


Clostridium haemolyticum

  • Causes bacillary haemoglobinuria in cattle, occasionally sheep
  • Endogenous infection - endospores dormant in liver
  • Fluke migration allows germination
  • Beta toxin causes intravascular haemolysis and hepatic necrosis
  • Haemoglobinuria due to destruction of red blood cells


Clostridium sordelli


Diagnosis

  • Anaerobic transport medium
  • Culture on blood agar enriched with yeast extract, vitamin K and haemin
  • Anaerobic culture with hydrogen supplement and 5-10% carbon dioxide
  • C. perfringens colonies are surrounded by a zone of double haemolysis
  • Biochemical tests
  • Toxins identified in body fluids by toxin neutralisation or protection tests in lab animals
  • Fluorescent antibody tests for histotoxic clostridia
  • ELISA, PCR for toxin detection