Anaerobic Bacterial Infections

Question 1

What are the three ways that anaerobic bacterial infections occur

Answer 1

1. Disruption to the mucous membrane (anaerobic bacteria enter sterile site causing infection e.g. urinary tract infection)
2. Skin wound being inoculated with foreign anaerobic bacteria (e.g. C. tetani)
3. Anaerobes grow to the extent that oxygen is consumed, creating an anaerobic environment which leads to flourishing of the anaerobes

Question 2

What are the risk factors for an anaerobic bacterial infection?

Answer 2

Disruption of mucous membrane

• e.g. surgery or trauma

Decrease oxygen in tissue

• e.g. tissue necrosis or ischemia

Dirty skin wounds

Question 3

What are the indicators of an anaerobic bacterial infection?

Answer 3

1. Close to a mucous membrane
2. Abscess formation
3. Infection persists after aminoglycoside abx (used to treat aerobic bacterial infections)
4. Foul odour
5. Gas production
6. Dark brown, black or brick-red fluorescence
7. Distinctive morphology of microbiota

Question 4

Why is the process of diagnosis difficult? How are these difficulties overcome?

Answer 4

It is a difficult process because anaerobic conditions must be maintained during specimen collection, transport, storage, culture and testing.

This is done in several ways, the most effective of which is using fluid aspirates with a syringe.

Question 5

Bacteroides fragillis

Answer 5

• Is the most common pathogenic anaerobic gram-negative rod
• Normal in the gut of healthy people
• Infections from faecal contamination of sterile site in the abdominal and gynaecological regions, as well as in skin and soft tissue (especially animal bites)
• It is very resistent to antibiotics and cannot be prevented because it is important in the gut

Question 6

Clostridium perfringens

Answer 6

• Large spore forming gram-positive rods
• Grows fast
• Soft tissue infection:
  
  • discolouration
  • gas formation (gas gangrene)
  • edema
  • tissue destruction
  • systemic spread
  • high mortality
• Caused by food poisoning
• Normal inhabitants of animal and human intestines
• Spread in faeces contaminated soil and water
• Treatment of soft tissue infection includes rapid aggressive debridgement and high dose penicillin
• Prevention is good wound care

Question 7

Clostridium tetani

Answer 7

• Large, motile sporulatng gram-positive rods
• Causes tetanus
• Grows locally, releases tetanospasmin toxin
  
  • Unregulated excitation of motor neurons
  • Uncontrollable muscle spasms (spastic paralysis)
  • Lock-jaw (trismus)
  • Back spasms (opisthotonus)
  • Fixed ‘smile’ (risus sardonicus)
  • Facial paralysis
• Spores located in soal
• Treatment: debridement, atibiotics (only prevents growth, toxin still active), tetanus immunoglobulin
• Prevention: tetanus toxoid vaccination
• Generalised, cephalic, localised and neonatal form

Question 8

C. botulinum

Answer 8

• Large sporulating, gram positive rods
• Causes botulism
• Releases botulinum toxin
  
  • Inability to contract muscles
  • Flaccid paralysis
  • Death through respiratory paralysis
• Common in soil and water
• Rare
• Infant votulism: colonisation of GIT
• Foodborne butulism: growth in non-acidic bottled or canned foods