Clostridioides difficile

• Describe Clostridioides difficile

  This is a gram positive, rod shaped, obligate anaerobe that produces exotoxins, which result in a spectrum of disease from diarrhoea to pseudomembranous colitis. It is a major nosocomial infection due to the use of colonic bacteria killing antibiotics in hospitals, which reduce the natural flora of a patient and therefore limit their colonisation resistance. It is the most common cause of infectious diarrhoea in hospitals with up to 35% of cases resulting in recurrent infections.
• Describe the symptoms of the disease caused by C. difficile

  Asymptomatic colonisation results in mild diarrhoea with potential development of more serious symptoms such as abdominal pain, fever and leukocytosis. Sever infection is characterised by inflammatory lesions, formation of pseudo membranes in the colon, bowel perforation and sepsis.
• Describe diagnosis or C. difficile disease

  • Foul smelling diarrhoea
  • Culture of organism on selective media in anaerobic environment following by cell toxicity assay, however, this is time consuming and technically difficult
  • Key consideration is that culture alone cannot differentiate asymptomatic colonisation form infection so need to test whether the bacteria are producing toxins
• Treatments for symptomatic C. difficile infection

  • Stop precipitating antibiotic treatments
  • Begin new antibiotic regimen:
  • Vancomycin, used in severe cases
  • However, these antibiotics impact gut microbiome, leading to recurrent infections
  • Managing severe disease is very challenging and is limited to surgical removal of colon.
  • Alternative approach- faecal microbiota transfer
• Describe some of the improvements for the FMT approach

  • Address the use of undefined materials with potential unintended consequences
  • Identify which species with the faecal microbiota can protect against C. Difficile infection
  • Recent paper identifed bacterial species associated with protect in mouse model of C. Difficile infection
• Describe the first FDA approved FMT-based treatment ofr C. difficile infection

  • Rectally administered suspension of faecal microbiota- approved November 2022
  • 70.6% success rate at 6 weeks
  • Still uncharacterised with diverse range of unidentified microorganisms present
  • No evaluation of long term complications
• Describe the key virulence factors of C. difficile

  Cytotoxins-

  • TcdA and TcdB cause secretory diarrhoea and colonic mucosal inflammation
  • disrupt actin cytoskeleton and tight junctions
  • results in lower trans epithelial resistance, fluid accumulation and destruction of epithelium

  Surface layer proteins- glycosylated proteins on cell surface

  Sporulation- spread within hospital environment and resistant to desiccation, chemicals and high temp.
• Describe the genes of the toxin pathogenicity locus in C. difficile

  TcdA and TcdB are encoded on the pathogenicity locus with an additional 4 genes; TcdC(negative regulation of tcdAB), TcdR (transcriptionally activating expression of TcdAB), TcdE (pore-forming protein involved in TcdAB secretion) and TcdL (non-functional fragment, role unclear). The highly virulent C. difficile strain NAPI/027 is characterised by a deletion in the TcdC locus.
• Describe the action of the TcdA and TcdB cytotoxins

  • belong to large clostridial toxin family
  • single chain proteins composed of 4 functional domains
  • amino terminal catalytic domain with glucosyltransferase activity
  • autoprotease domain
  • delivery domain for receptor binding, pore formation and toxin translocation
  • Carboxy terminal combined repetitive oligopolies sequences domain
• Describe the function of TcdA and TcdB

  These toxins glycosylated small GTPases, such as Rho and Ras, to render them inactive and leading to cytoskeleton changes within the host cell. They are capable of binding a diverse range of receptors and are take up by endocytosis. Lower pH in the endosome stimulates a conformational change in TcdAB, which leads to pore formation and exit of AP domain and GT domain, which go on to inactivate GTPases.