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
2
Q
Anaerobic culture methods
A
- Anaerobic chamber
○ Gas mix with no oxygen
Wall with low oxygen permeability
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
4
Q
C.difficile spores have an exosporium
A
Help stick to surfaces and interact with the host
5
Q
The pathogenic clostridia
A
- Common feature - produce potent protein toxins
If they lose this feature they are not pathogenic
6
Q
Neurotoxic clostridia
A
Clostridium tetani
Clostridium botulinum
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
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
- Pathogenesis
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
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
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
12
Q
Tetanus vs Botulism
A
- Tetanus toxin blocks the relaxation pathway - rigid paralysis
Botulism blocks the contraction pathway = flaccid paralysis
13
Q
Enterotoxic clostridia
A
Clostridium perfringens
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
- Can cause food poisoning
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
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
- Patient resistant to CDI if NM is not disrupted
- When antibiotic treatment commences, infection with resistant strain more likely while antibiotic is being administered
- 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
C.difficile Major virulence factors
A and B toxins
26
Intestinal integrity and maintenance
- Relies on cellular polarity
- Formation and maintenance of tight junctions
Renewal of the stem cell production and maintenance of stem cell niche
27
Cell polarity
- 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
Formation and maintenance of tight junctions
- Adherens junctions (AJ) maintain intestinal integrity
- Connect actin cytoskeleton between cells
Disruption of AJ can exacerbate colonic inflammation – ‘leaky’ gut
29
Renewal of the stem cell production and maintenance of stem cell niche
- 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
C. difficile infection damages colonic stem cells
- Organoid culturing was used to determine that C. difficile infection affects stem cell function and gut repair capacity
- Acts like mini gut
31
CDI alters stem cell function and organoid formation
- 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
Do the toxins affect human organoid function
- Toxin a is doing some damage
| But toxin B is completely destroying the cells
33
Summary of C. difficile infection:
- 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
C.difficile can cause leaky gut
Dissemination through severe diseases
35
Current C. difficile treatments
- 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
New treatments under consideration
- Probiotics
- Intravenous IgG antibodies (containing ant-toxin IgG)
- Monoclonal antibodies
- Passive polyclonal immunotherapy
Faecal transplant therapy (controversial)
37
C.difficile infections of animals
- 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
Symptoms of Clostridium perforens
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
Symptoms of Clostridium perfringens
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
