Clostridia

What are they?

Clostridia are large, Gram-positive anaerobic bacilli, which produce exo-toxins and spores.

This section will look at four key Clostridia bacteria.

Clostridium perfringens

Clostridium perfringens is a non-motile bacteria which has a polysaccharide capsule present.

Virulence Factors

• Exotoxins (A-E) – the alpha toxin is the most important, being Phospholipase C. Phospholipase C converts phosphatidylcholine into diacylglycerol. This toxin is detected using the Nagler Reaction, which has agar containing lecithin. The plate is covered in the toxin and half of the plate has the anti-toxin present as well. The toxin will cause the lecithin to be broken down and a precipitate will form – a positive test will be where there is no precipitate under the anti-toxin.
• Enterotoxins which will cause food poisoning like symptoms.

Diseases

• Gas gangrene – spores of the bacteria are picked up in wounds. It leads to oedema, gas production, necrosis and toxaemia. The main treatment is to remove dead and infected tissue as well as high dose (IV) antibiotics.
• Food poisoning
  • An incubation period of ~12 hours
  • Main symptoms are of diarrhoea and abdominal cramps (fever and vomiting is uncommon)
  • Usually cleared in 24-48 hours

Clostridium tetani

Clostridium tetani leads to the development of tetanus. It is a motile bacteria which has ‘drumstick‘ like spores. It is typically picked up from the soil in to open wounds. The incubation period is 10-14 days. The bacteria can pass into the central nervous system.

Virulence Factors

• Neurotoxin – the presence of tetanospasmin which causes spastic paralysis
• Zinc endopeptidase – this breaks down synaptobrevins and prevents the release of aminobutyric acid, an inhibitory neurotransmitter.

Treatment and Prevention

• Treatment is using penicillin, metronidazole and anti-toxin
• Prevention occurs through a vaccine which uses a toxoid

Clostridium botulinum

Clostridium botulinum leads to the development of botulism. This is a motile bacteria with the presence of a sub-terminal spore. Incubation is roughly 1-2 days, with the bacteria being picked up from the soil in to wounds. Symptoms include flaccid paralysis, drooping eyelids, respiratory and cardiac failure. Also referred to as ‘floppy baby syndrome’.

Virulence Factors

• Neurotoxin – 7 types from A-G with A, B and E are most important
• Zinc endopeptidase – blocks the release of acetylcholine and therefore doesn’t allow neurotransmission.

Treatment

• Treatment is by using a polyvalent anti-toxin.

Clostridium difficile

Clostridium difficile leads to the development of pseudomembranous colitis and antibiotic-associated diarrhoea. This is a major hospital-associated infection in individuals who are on broad-spectrum antibiotics.

Virulence Factors

• Two main toxins – TcdA (catalytic domain) and TcdB (binding domain) – these can be identified in the patient’s stool and is a diagnostic marker. The catalytic domain is released in the cytoplasm and TcdB causes damage to surrounding tissue.
• Inactivation of Rho (GTPase) also occurs which causes actin condensation, subsequent membrane blebbing and apoptosis. This stimulates neutrophil activity and therefore fluid accumulation.

Treatment and Prevention

• Prevention involves avoiding giving patients broad-spectrum antibiotics if they are at risk and also carrying out good cross-infection procedures.
• Treatment involves removing the broad-spectrum antibiotic (e.g. clindamycin) and then treating with metronidazole or vancomycin.

Clostridia Summary

• Clostridia bacteria are large, Gram-positive anaerobic bacilli, which produce exo-toxins and spores.
• Cl. perfringens leads to gas gangrene and food poisoning.
• Cl. tetani leads to tetanus.
• Cl. botulinum leads to botulism.
• Cl. difficile leads to pseudomembranous colitis and antibiotic-associated diarrhoea.

Quiz

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References and Recommended Reading

• Essentials of Microbiology for Dental Students
• Infectious Disease Essentials