Lecture 8 Clostridium Difficile I Flashcards
What are the diagnostic methods of clostridium difficile?
It is a gram positive rod
After performing a gram stain a spore stain can be performed
If a positive spore stain result is achieved then it must be either a bacillus or clostridium bacteria
Then an oxidase or catalase test can be used to distinguish between these two genera and an elisa based test can be used to check for the toxins of clostridium
What are the general features of clostridium?
Gram positve-anaerobic-rod-capable-of-forming-endospores
causes antibiotic associated-gastrointestinal-diseases ranging from benign diarrhea to severe pseudomembranous colitis
What are the epidemiological features of clostridium dificile?
Colonizes the intestines of some healthy individuals
Exposure to certain antibiotics can result in overgrowth of C.difficile causing endogenous infection
Exogenous infection can occur through spores shed by infected patients and the faecal oral route of transmission
The spores produced by clostridium are able to remain viable for a long period of time and resistant to most cleaning methods
Domestic and farm animals can also be a soruce of C.diff infection
What are the features of the endospores?
They are produced by several bacterial species and are dormant non-reproductive structures which are resistant to heat, radiation and dry conditions
What is the pathogeqnesis of C. Difficile?
There is disturbance of the normal intestinal homeostasis by certain, broad spectrum antibiotics which reduces the colonisation resistance to C. Difficile this can lead to a loss of intestinal homeostasis, changes in mentabolites and initiation of innate immune responses that can promote inflammatory responses
What are the key virulence factors in C. Difficile?
Toxin A, Toxin B which are the primary virulence factors
Binary toxin (CDT) which is not found in many species
Flagellin, S-Layer and fibronectin-binding protein may also be virulence factors though this is unclear
What is PaLoc in Clostridium Difficile?
It is the pathogenicity locus is found in all virulent strains of C.Difficile but not in any of the avirulent strains
What is contained in PaLoc in C. Difficile?
TcdA: Which codes for toxin A
TcdB: Which codes for Toxin B
TcdR: An alternative sigma factor critical for expression of toxin genes
TcdC: Negative regulator of toxin production, blocks the association TcdR with RNAP
TcdE: A gene with homology to bacteriophage holins possible to function in protein secretion but function is still debated
What is the domain structure of toxin B in C. Difficile?
It is 2366 amino acids long
There is a catalytic domain with a DXD motif to represent the catalytic site
There is a translocation domain which has a hydrophobic region important for delivery of the catalytic domain into host cell cytosol the cysteine protease domain used for auto cleavage
There is a binding domain of polypeptide repeats that bind host cell receptor
What are Large clostridial glycosylating toxins?
A family of clostridial toxins which all have the same monoglucosyltransferase enzymatic activity
The family includes toxin A and B of C. Difficile
They are all large proteins and highly toxic
What is the role of toxin A/B in C. Difficile pathogenesis?
The toxins cause cytoskeletal changes, disruption of tight junctions, cell death, loss of the epithelial barier, attraction of immune cells, inflammation
This results in severe damage to intestinal epithelium
What is the controversy around toxin A and B of C. Difficile?
Both toxins have the same function and probably evolved from gene duplication
It appears that each toxin may having differing importance able to cause disease in different species
What is the function of binary toxin of C. Difficile?
It is an AB famiy toxin where the B subunit binds to host cell via lipolysis-stimluated lipoprotein receptor forming heptamers after proteolytic activation
The A subunit has ADP-ribosyltransferase activity with actin as the substrate
What is the role of C. Difficile binary toxin and disease?
It is only found in 027 strains which makes up a total of 10% of human isolates but there is a correlation between it and more severe disease
How is CDT processed?
It enters the cell via receptor mediated endocytosis
There is acidification of the endosome
A pore is formed and the A subunit is delivered into the cytosol
There is ADP-ribosylation of monomeric actin preventing its polymerisation leading to destruction of he actin cytoskeleton
This causes changes in the microtubule system leading to the formation of protrusions which can help bacterial attachment to the host cell
