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2052 DYLAN > clostridium > Flashcards

clostridium Flashcards

1
Q

Characteristics of clostridium

A
  • Gram +ve
    • Obligate anaerobes
    • Form heat resistant endospores
    • Common inhabitants of GI tract
      Important in humans and animals pathogens
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2
Q

Anaerobic culture methods

A
  • Anaerobic chamber
    ○ Gas mix with no oxygen
    Wall with low oxygen permeability
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3
Q

Clostridial endospores

A
  • Form endospores under adverse environmental condition
    ○ Under the presence of oxygen
    ○ Otherwise oxygen would kill the clostridium
    ○ Spores are the survival mechanism
    Characterised on basis of position, size and shape
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4
Q

C.difficile spores have an exosporium

A

Help stick to surfaces and interact with the host

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5
Q

The pathogenic clostridia

A
  • Common feature - produce potent protein toxins

If they lose this feature they are not pathogenic

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6
Q

Neurotoxic clostridia

A

Clostridium tetani

Clostridium botulinum

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7
Q

Clostridium tetani

A

○ Causative agent for tetanus
○ Produces tetanus toxin
§ Neurotoxin
○ Pathogenesis
§ Entry of spore into deep wound
§ Germination of spore in anaerobic environment
§ Production of toxin released when they die
§ Toxin bind to nerve endings and translocated into nerve cells
§ Inhibits neurotransmitter release
Blockage of muscle relaxation pathway

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8
Q

Clostridium botulinum

A
  • Agent for botulism
    ○ Food-borne
    ○ Poorly heated contaminated food
    • Pathogenesis
      ○ Spores germinate in food and toxin produced during vegetative growth
      ○ Pre-formed toxin is ingested with food
      ○ Toxin localises in neuromuscular junction
      Blocks release of neurotransmitter
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9
Q

Pathogenesis of tetanus

A
  • Results in uncontrolled stimulation of muscles
    ○ Tension, cramping, spasms, paralysis
    ○ Death from spasms of diaphragm
    Vaccination using tetanus toxoid is an effective preventative measure
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10
Q

Pathogenesis of botulism

A
  • Results in an uncontrolled relaxation of muscles
    • Symptoms occur within 18-24 hrs of ingestion
    • Flaccid paralysis
    • Death due to cardiac failure
    • No vaccine
      Can treat with antitoxin if administered quickly
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11
Q

Therapeutic use of botulinum neurotoxin

A
  • Injection of low levels of boNT (reversible)
    • No effect on anatomical contact between nerves and muscle
    • BoNT used to treat severe focal dystonia
    • BoNT used in cosmetic industry
      Very safe
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12
Q

Tetanus vs Botulism

A
  • Tetanus toxin blocks the relaxation pathway - rigid paralysis
    Botulism blocks the contraction pathway = flaccid paralysis
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13
Q

Enterotoxic clostridia

A

Clostridium perfringens

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14
Q

Clostridium perfringens

A
  • Aerotolerant anaerobe (wont grow but may not die in small amounts of oxygen) ; forms spores
    • Can cause food poisoning
      ○ Present in meat that has been heated and cooled slowly
      ○ Large amount of toxins
    • Produces enterotoxin
      ○ Bacterial cells sporulate in intestine
      ○ Production of enterotoxin is associated with sporulation
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15
Q

C.perfingens type D infections

A
  • Animal diseases
    • Make alpha toxin and epsilon toxin
    • Pathogenesis
      ○ Produces pr-epsilon toxin in intestine
      ○ Activated by trypsin
      ○ Increased intestinal permeability
      ○ Absorbed systemic circulation
      ○ Endothelial cells of brain, kidney etc
      Epsilon-toxin is essential for type D disease
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16
Q

Histotoxic clostridia

A

Clostridium perfringens

17
Q

Clostridium perfringens

A

○ Causes gas gangrene
§ Injured tissue becomes contaminated with spores
§ If tissue is anaerobic spores germinate and bacteria grow
§ Extensive bacterial growth
○ Produces a-toxin
§ Phospholipase
§ Disrupts host-cell plasma membrane
§ Extensive destruction of cells and tissue
§ Symptoms - sever pain, oedema, necrosis
Treatment - radical and usually involves amputation

18
Q

Human - microbiome advantage

A 
- Microbiome
		○ Nutrients
		○ Stable environment
		○ Constant temp
		○ Protection
		○ Transport
	- Host
		○ Nutritional benefit
Prevention of colonisation of pathogens
19
Q

Non-specific immunity by normal microbiota

A
  • Producing metabolic products - bacteriocins - inhibit growth of bacteria
    • Adhering to target cells
    • Depleting nutrients essential for pathogens
      Stimulating immune system so it is primed to fight pathogens
20
Q

Destruction of NM by antibiotics can cause

A
  • Candida and C. difficile
    ○ Held in check by NM
    ○ Not killed by antibiotics
    C.difficile overgrows intestinal tract - toxin - antibiotic associated colitis
21
Q

Clostridium difficile

A
  • Leading cause of infectious diarrhoea
    • Also a problem in animals
    • Strict anaerobic and spore former
      C.difficile only colonises gut when the NM is disrupted
22
Q

Antibiotic and C. difficile infection

A
  1. Patient resistant to CDI if NM is not disrupted
    1. When antibiotic treatment commences, infection with resistant strain more likely while antibiotic is being administered
    2. When treatment ceases, microbiota remains disturbed during which patients can be infected with resistant or susceptible C.difficile
      After microbiota recovers, colonisation resistance to C. difficile is restored
23
Q

C.difficile infectious cycle

A
  • Reduction of NM gut microbiota
    • Ingestion of spores - survive in stomach
    • Bile salts in small intestine trigger germination events
    • Anaerobic environment of the colon supports vegetative growth and toxin produced
      Spores shed
24
Q

C.difficile mediated pseudomembranous colitis

A

Yellowish plaques of fibrin, mucus and inflammatory cells overlay NM intestinal mucosa

25
Q

C.difficile Major virulence factors

A

A and B toxins

26
Q

Intestinal integrity and maintenance

A
  • Relies on cellular polarity
    • Formation and maintenance of tight junctions
      Renewal of the stem cell production and maintenance of stem cell niche
27
Q

Cell polarity

A
  • Intestinal epithelial cells are polarised
    • Cellular polarity is important for intestinal homeostasis
    • Ezrin is important for apical integrity in intestinal epithelial cells
      ○ Apical membrane (top) is opposite to basolateral membrane (bottom) of the cell
      Ezrin gets disrupted
28
Q

Formation and maintenance of tight junctions

A
  • Adherens junctions (AJ) maintain intestinal integrity
    • Connect actin cytoskeleton between cells
      Disruption of AJ can exacerbate colonic inflammation – ‘leaky’ gut
29
Q

Renewal of the stem cell production and maintenance of stem cell niche

A
  • The gut is the most rapidly proliferating tissue in adult mammals and the intestinal epithelium is constantly replaced
    • Stem cells at the base of the epithelium give rise to new cells
      Migrate to crypt surface and are sloughed off through apoptotic death
30
Q

C. difficile infection damages colonic stem cells

A
  • Organoid culturing was used to determine that C. difficile infection affects stem cell function and gut repair capacity
    • Acts like mini gut
31
Q

CDI alters stem cell function and organoid formation

A
  • Organoid culturing was used to determine if C. difficile infection affects colonic stem cell function and gut repair capacity
    infection reduces stem cell function ex vivo
32
Q

Do the toxins affect human organoid function

A
  • Toxin a is doing some damage

But toxin B is completely destroying the cells

33
Q

Summary of C. difficile infection:

A
  • Colonic structure is disrupted
    • Integrity mechanisms are perturbed
      ○ Adherens-junctions (cell-to-cell contacts)
      ○ Ezrin (cell polarity
    • Stem cells and niche are damaged; repair capacity disrupted
      These effects result in severe damage and disease.
34
Q

C.difficile can cause leaky gut

A

Dissemination through severe diseases

35
Q

Current C. difficile treatments

A
  • Discontinue antibiotic that cause C. difficile
    • More antibiotics
      ○ Oral metronidazole and or vancomycin
      § Relapses occur
      Vancomycin has a narrow host range so it doesn’t kill as much of the microbiota - fewer relapses
36
Q

New treatments under consideration

A
  • Probiotics
    • Intravenous IgG antibodies (containing ant-toxin IgG)
    • Monoclonal antibodies
    • Passive polyclonal immunotherapy
      Faecal transplant therapy (controversial)
37
Q

C.difficile infections of animals

A
  • Under-recognised cause of disease in animals
    • No estimates of economic burden
    • Can be detected in meat products
      Can be detected in water runoff and compost
38
Q

Symptoms of Clostridium perforens

A

Onset of symptoms after 8 to 16 hours
○ Water diarrhoea, nausea, abdominal cramps
- Pathogen to both humans and animals
○ Humans - food poisoning, gangrene
○ Animals - enterotoxaemic diseases (C. perfringens causes a lot of animal diseases)
○ Produces up to 22 toxins
Vaccines are toxin-based

39
Q

Symptoms of Clostridium perfringens

A

Onset of symptoms after 8 to 16 hours
○ Water diarrhoea, nausea, abdominal cramps
- Pathogen to both humans and animals
○ Humans - food poisoning, gangrene
○ Animals - enterotoxaemic diseases (C. perfringens causes a lot of animal diseases)
○ Produces up to 22 toxins
Vaccines are toxin-based

2052 DYLAN (12 decks)

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