Anaerobic Bacteria Flashcards
(21 cards)
What are the two main types of anaerobic microorganisms
- ) OBLIGATE ANAEROBES:
- Harmed by presence of oxygen - ) FACULATIVE ANAEROBES:
- Can grow without oxygen but use oxygen if present
How do we study anaerobes in the lab
- Special culture methods to exclude o2 and study gram stain, spore stain
- Anaerobes are sensitive to metronidazole
Clostridium species
- Large, straight, gram +ve bacilli (anaerobic)
- Produces endospores - allows for growth again when conditions are favourable
- Produces exo-toxins
- Important species in prominent diseases:
Cl. perfringens (gangrene, food poisoning)
Cl. botulinum - food
Cl. tetani - tetanus
CI. difficile - pseudomembranous colitis
Cl. perfringens
• Capsulated, non-motile, Gram +ve rod
- Polysaccharide capsule , repeating units of 6 sugars
What is the major exo-toxin of Clostridium species (5 types)
• ALPHA (a) TOXIN
- Lyses RBCs, platelets, leukocytes & endothelial cells
- Inflammation, major swelling
- Oedema, bleeding
- Haemolysis
- Kidney damage - renal failure
- Myocardial dysfucntion
OTHER VFs:
- Proteases & hyaluronidase - destroy tissue
- Enterotoxin: Pore-forming, produced upon sporulation of ingested bacteria in stomach acid reaction
Diseases causes by Cl.perfringens
GAS GANGRENE:
(clostridial myonecrosis)
- Spore contamination of wound (soil, animal faeces)
- Oedema, gas formation, necrosis, toxaemia, cellulitis
• Treatment:
- Surgery (amputation), antibiotics
Food Poisoning in Cl.perfringens
Incubation 10-12hr
- Cl.p spores in soil and animal gut
- C.pl then grows in food meats
- Spores survive cooking and germinate in food
- Food is then ingested
- Bacteria sporulate, bacterial cells ingested and produce enterotoxin in stomach
- This leads to intestinal epithelium damage and inhibition of glucose transport
Tetanus - serious Cl. infection
- Acute spastic paralysis caused by a potent bacterial neuro-exotoxin
- Characterised by lockjaw (truisms) and ricus sardonic
- Caused by uncontrolled contraction of muscles - mostly in CNS
Cl. tetani
- Incubation 10-14 days
- Enters body through wounds, splinters, cuts
- Spores ubiquitous in the environment (soil)
- Spores in soil contaminate wounds
- Grows in wound, toxin released into body and tracks along nerves to CNS
This is a motile cl. so will see spreading on agar
Tetanus toxin
Classic A-B neurotoxin
- A domain contains active site
- B domain > carbohydrate receptor binding
A-domain: (Zinc endopeptidase)
- Breaks down synaptobrevins
- Prevents release of inhibitory transmitter (Gamma-aminobutyric acid - a muscle relaxant
How do we treat tetanus
- Anti-toxin/Immunoglobulin + penicillin + metronidazole
- Prevention by immunisation with tetanus toxoid
kills 50% of infected patients
Botulism
Caused by ingestion of preformed toxin from contaminated food containing Cl. Botulinum bacteria
- Mostly in food thats been heated then cooled and stored for long-periods
- Flaccid paralysis
- Drooping eyelids, progressive motor loss, dizziness
- Respiratory & Cardiac failure
Cl. botulinum
• Motile gram +ve bacillus
- Sub terminal spores
- Distributed in soil
- Optimum growth 35 degrees, some can grown 1-5 degrees
Botulinum toxin
- Potent neurotoxin
- A domain (zinc endopeptidase):
- Affects peripheral cholinergic synapses
- Blocks release of acetylcholine
- Irreversible binding
Treatment:
- Remove toxin
Botox
• Because it can weaken muscles temporarily when injected in small amounts:
- Strabismus
- Bruxism
- Torticolis
- Muscle spasms in cerebral palsy
C. difficile - Antibiotic associated diarrhoea
- Associated with broad-spectrum antibiotic use, clindamycin & ampicillin
- Outcompetes rest of population after antibiotic course complete
- Spore-forming - resistant to heat and disinfectants, shed in faeces
- Severe diarrhoea
- Two exotoxins A & B
- Pseudomembranous colitis: bowel disease - can lead to rupture
Cl. Difficile treatment
• Vancomycin or Metronidazole
Remove selective antibiotic
• Preventing: cleaning, hand-washing, quarantine
Limit use of broad-spectrum antibiotics in ‘at risk’ patients
OTHER ANAEROBES
Gram -ve
- Bacteroides - abdominal wound infection
- Prevotella
- Fusobacterium
Gram +ve
- Eubacterium
- Gardnerella
- Bifidobacterium
Prevotella
Gram -ve black pigmented anaerobe. non motile, rod shape
- In oral cavity, Prevotella colonise by binding or attaching to other bacteria in addition to epithelial cells
- Abscesses, wound infection, bite infections, genital tract infections and periodontitis
Porphyromonas
Periodontal disease
- Non motile, gram -ve
- Forms black colonies on blood agar
Fusobacterium
- Long rod/spindle shaped bacilli, gram -ve
- Associated with periodontal disease, skin ulcers, respiratory infections
Treatment:
- Antibiotics (clindamycin, chloramphenicol)
