2- C. difficile infection Flashcards
describe the microbiology of the C. difficile bacteria
gram-positive, anaerobic and spore-forming = hard to clean spores or get rid of them from the environment
exists asymptomatically in the gut - colonises approx. 5%
produces three toxins
list the three risk factors for developing C. difficile infection
antacids
antibiotics (incorrect use, general use)
prolonged hospital stays
how do antibiotics contribute to C. difficile infections?
antibiotics disrupts the normal microbial ecosystem/microbiome of the gut - affects the balance of bacterial populations
disruption provide a competitive advantage for spore-forming anaerobic bacteria like C. difficile over other anaerobic bacteria
antibiotics create a favourable environment for the colonisation and growth of C. difficile
give examples of antibiotics more strongly associated with C. difficile infections (3)
2nd and 3nrd gen. cephalosporins
quinolones
clindamycin
C. difficile normally exists asymptomatically in a healthy gut - how?
normally controlled at low levels by the diverse popl. of gut bacterial species – e.g. lactobacilli - kept within an ecological balance
it’s only when the ecological balance is disrupted that C. difficile will overgrow and colonise the gut
what are the two main components of the AB toxin produced by Clostridium difficile?
- receptor binding domain = facilitates binding to host cell receptors and internalisation
- enzymatic proteins = GTD and CPD (glucosyltransferase domain and cysteine protease domain)
what are the two main cytotoxins produced by C. difficile? how do they contribute to pathogenesis?
- cytotoxin A (TcdA)
- cytotoxin B (TcdB)
the toxins act intracellularly as type III AB toxins, disrupting normal cellular processes
A component of AB toxin has glycosylating enzymes
describe the pathogenesis mechanism of C. difficile
cytotoxins A and B bind to a specific receptor on enterocytes of the gut epithelium, and are internalised in an endosome
endosome is acidified and a pore forms in the endosome - allows for the translocation of AB toxin components - e.g. GTD - into the cytoplasm
GTD is released into the host cytoplasm, block/ inactivates Rho GTPases through glycosylation - has cellular cytopathic and cytotoxic effects:
cytopathic effects:
- cytoskeleton breaks down
- loss of cell-cell contacts = e.g. intercellular junctions which affects cell integrity
- increased epithelial permeability
cytotoxic effects:
- activation of the inflammasome
- increase in ROS levels
- induces apoptosis/ programmed cell death
describe the cellular cytopathic effects
cytoskeleton breaks down
loss of cell-cell contacts = e.g. intercellular junctions which affects cell integrity
increased epithelial permeability
describe the cellular cytotoxic effects
activation of the inflammasome
increase in ROS levels
induces apoptosis/ programmed cell death
list the major cytopathic and cytotoxic effects of C. difficile
patchy necrosis = areas of cell death in gut tissue with inflammation, full of bacteria and dying leukocytes and neutrophils
epithelial ulcers
formation of pseudomembranes = accumulations of leukocytes, fibrin, cell debris and mucus, indicating an immune response
name three severe conditions associated with C. difficile
pseudomembranous colitis
toxic megacolon
peritonitis
list methods used to diagnose C. difficile (5)
- clinical signs and symptoms
- raised WBC count
- two phase test:
1. a GDH (glutamate dehydrogenase) test detecting C. difficile organisms,
2. toxin enzyme-linked immunosorbent assay (ELISA) = detects TcdA and B in stool samples - PCR reaction
- colonoscopy in severe cases to assess damage
what is the treatment for C. difficile?
antibiotics not recommended - some can be helpful
faecal transplant for recurrent infections
surgery to removed damaged parts of the colon
removing the offending antibiotic
