GITI Flashcards
What are the characteristics of a GI infection?
1) food acts as a vehicle for transmission: food handlers contaminate the food and consume the pathogen
2) toxins may be present in the food
3) Broad-spectrum antibiotics disrupt normal gut flora causing over growth of pathogens
What are the characteristics of C.Difficile?
-gram positive rod
-strictly anaerobic
-spore forming
What are the symptoms of C.Diff?
- Watery Diarrhoea
- Nausea
- Dehydration
- Cramping abdominal pain
How do spore forming bacteria grow?
1) divide by binary fission
2) when nutrients are depleted, spore formation is initiated
3) dna condenses and aligns itself in the middle of the cell -> becomes known as the mother cell
4) Dna divides and forms forespore which is engulfed by mother cell
5) Protein coat forms around spore, spore is released from mother cell
What are the risk factors for C.Diff?
- spores: persistent and transmissible, resistant to antimicrobials
- hospitalisation and BS antibiotic use, hygiene, contaminated equipment
Why can C Diff spores pass through the stomach?
They are highly resistant to stomach acid
What antibiotics are associated with c.diff?
clindamycin and ciprofloxacin
What happens to C Diff spores after they reach the small intestine?
- the spores encounter favourable conditions: bile salts, mildly acidic PH
- this triggers germination of spores -> produces C Difficile vegetative cells which are metabolically active
Which toxins do vegetative C Diff cells produce and what affect do they have?
- Toxin A (enterotoxin) and B (cytotoxin)
- damage lining of the colon: inflammation, diarrhoea, pseudomembranous colitis (severe inflammation and ulceration of colon)
How are C Diff spores spread from the patient?
- C Diff cells in colon produce spores which are secreted in patients diarrhoea
- highly resistant
What are the 3 main steps in germination?
- spores lose their heat resistance and release ions as well as calcium stored in their heat complex
-the spores core absorbs water and enzymes breakdown the cortex and other protective proteins
-this reactivates its metabolism -> metabolically active - makes it sensitive to antibiotics
How does C Diff carry out cell adhesion?
- it has S layer proteins which attach to the cells lining the gut -> adherence is essential for bacteria to establish an infection
- flagella allows It to reach areas in the gut
Where are toxin A and B encoded onto?
Pathogenicity Locus (PaLoc)
What is the mechanism of action for Toxins A and B?
(Toxin A) binds to enterocyte brush border, forms pores in endosomal membrane, endosomal content enters cytosol and damages cells
(Toxin B) disrupts cytoskeleton -> diarrhoea -> induces apoptosis of enterocytes
-modify Rho GTPase proteins which are important for maintaining the structure and function of gut lining cells
What are the complications of C.Diff?
Bloody diarrhoea
constipation
What symptoms occur when tight junctions are weakened and why do they occur?
- diarrhoea and inflammation: toxins, bacteria leak through the gut lining due to toxins A and B inactivating Rho proteins
What are the key features of C Difficile ribotype 027?
produces higher than normal levels of toxin A and B
-causes base pair deletion in toxin regulating gene -> makes it more deadly
- resistant to ciprofloxacin and moxifloxacin
What are the complications of a C.Diff infection?
toxic megacolon: severe inflammation and dilation of the colon
How would you diagnose C Difficile associated Diarrhoea?
- clinical sample: faeces (glutamate dehydrogenase)
- antigen detection is initial screening test
- non culture techniques: toxin detection, selective agar and ribotyping
What are the 2 ways of carrying out toxin detection?
1) Enzyme immunoassay for toxin a and b in stool - rapid but not sensitive
2) pcr detecting toxin B in stool
What are the types of lab tests we do for C Diff?
1) cell culture cytotoxin on stool - highly sensitive, highly specific but time consuming
2)enzyme immunoassay detecting glutamate dehydrogenase antigen in stool
3) colonoscopy
4) hematoxylin and eosin stain
What are some treatments for C Diff?
- oral antibiotics: vancomycin and fidaxomicin
replacement fluid and electrolytes - discontinuing precipitating antibiotics
- biotherapy: aims to restore gut microbiome
How can C Diff be prevented?
using narrow spectrum antibiotics
isolating patients
eliminating spores from the environment
