Clostridium species

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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

Neurotoxic clostridia

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 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 perfringens type A

Gas gangrene
- Extensive bacterial invasion of damaged muscle
- Gas production causing subcutaneous crepitus
- Similar manifestations as malignant oedema

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

Causes gas gangrene, myositis and abomasitis (lambs)

Treatment of histotoxic infections

Early penicillin
Vaccination with bacterin or toxoid at 3 months and booster after 3 weeks, then annually

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 for 48 hours
Colonies of C. perfringens are 5mm diameter, circular, flat and grey
C. perfringens colonies are surrounded by a zone of double haemolysis
Positive cAMP test with Sreptococci agalactiae
Biochemical tests
Toxins identified in body fluids by toxin neutralisation or protection tests in lab animals
Nagler reaction to detect alpha toxin - plate neutralisation test
Fluorescent antibody tests for histotoxic clostridia
ELISA, PCR for toxin detection

Enteropathogenic and enterotoxaemic clostridia

General:
- Clostridium perfringens types B, C and D
- Found in soil, feaces and intestinal tract
- Survive in soil as spores
- Husbandry, changes in diet and environment predispose to proliferation in the intestine
Pathogenesis and pathogenicity:
- Clostridial replication and overgrowth in the interstinal tract of sheep
- Production of potent exotoxins which cause local and systemic effects of enterotoxaemia
- Type of toxins produced determine clinical syndrome
- Haemolysins, collagenases and hyaluronidases also produced
C. perfringens type A:
- Necrotising enterocolitis in pigs and necrotic enteritis in chickens
- Canine haemorrhagic gastroenteritis
- Typhlocolotis in horses, possibly associated with Colitis X
C. perfringens type B:
- Lamb dysentery
- Up to 30% morbidity and high mortality
- Affects lambs in first week of life
- Abdominal distension, pain, bloody faeces, sudden death
- Bacterial overgrowth in the intestine of the lamb due to immature bacterial flora
- Lack of proteases in the immature gut prevents cleavage of the beta toxin, allowing it to cause disease
- Haemorrhagic enteritis and ulceration in the small intestine
- Fluid in the peritoneal cavity and pericardial sac due to increased capillary permeability
- Fatal haemorrhagic enteritis in newborn foals, calves and adult goats
C. perfringens type C:
- Acute enterotoxaemia in adult sheep, 'struck'
- Sudden death or terminal convulsions in sheep at pasture
- Beta toxin plays major role in pathogenesis of the disease
- Post mortem: jejunal ulceration; hyperaemia in small intestine; fluid accumulation in peritoneal cavity; congestion of peritoneal vessels; petechial haemorrhages
- Haemorrhagic enteritis in piglets
  - Peracute enterotoxaemia often of entire litter with mortality rates 80%
  - Infection from sow's faeces
  - Death within 24 hours in young piglets
  - Chronic disease in older piglets
  - Dullness, anorexia, bloody faeces, perianal hyperaemia
  - Post mortem: necrosis of terminal small intestinal mucosa, caecum and colon and blood-stained contents; serosanguinous fluid in pleural and peritoneal cavities
- Necrotic enteritis in chickens:
  - Broilers under 12 weeks
  - Acute enterotoxaemia, sudden onset and high mortality
  - Necrosis of small intestine
  - Predisposing factors include diet changes, coccidial infection and intestinal hypomotility
- Acute enterotoxaemia with haemorrhagic enteritis in calves, lambs, foals
- Peritonitis in cattle
C. perfringens type D:
- Pulpy kidney disease in well-fed 3-10 week-old lambs
- Follows overeating high grain diet or luchious pasture
- Starch from partially digested food enterering the intestine from the rumen allows rapid clostridial proliferation
- Epsilon toxin activated by proteolytic enzymes causes toxaemia
- Lambs found dead or with opisthotonos, convulsions, coma in acute phases
- Blindness and head pressing in subacute disease; bloat in later stages
- Hyperglycaemia, glycosuria
- Post mortem: hyperaemia in intestine; fluid in pericardial sac; kidney autolysis with pulpy cortical softening (acute death)
- Subacute death causes symmetrical encephalomalacia and haemorrhage in basal ganglia and midbrain
- Enterotoxaemia in kids and adult goats

- Dysphagia in horses

C. perfringens type E:
- Enteritis in rabbits, haemorrhagic enteritis in calves