GITI

Question 1

What are the characteristics of a GI infection?

Answer 1

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

Question 2

What are the characteristics of C.Difficile?

Answer 2

-gram positive rod
-strictly anaerobic
-spore forming

Question 3

What are the symptoms of C.Diff?

Answer 3

• Watery Diarrhoea
• Nausea
• Dehydration
• Cramping abdominal pain

Question 4

How do spore forming bacteria grow?

Answer 4

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

Question 5

What are the risk factors for C.Diff?

Answer 5

• spores: persistent and transmissible, resistant to antimicrobials
• hospitalisation and BS antibiotic use, hygiene, contaminated equipment

Question 6

Why can C Diff spores pass through the stomach?

Answer 6

They are highly resistant to stomach acid

Question 7

What antibiotics are associated with c.diff?

Answer 7

clindamycin and ciprofloxacin

Question 8

What happens to C Diff spores after they reach the small intestine?

Answer 8

• the spores encounter favourable conditions: bile salts, mildly acidic PH
• this triggers germination of spores -> produces C Difficile vegetative cells which are metabolically active

Question 9

Which toxins do vegetative C Diff cells produce and what affect do they have?

Answer 9

• Toxin A (enterotoxin) and B (cytotoxin)
• damage lining of the colon: inflammation, diarrhoea, pseudomembranous colitis (severe inflammation and ulceration of colon)

Question 10

How are C Diff spores spread from the patient?

Answer 10

• C Diff cells in colon produce spores which are secreted in patients diarrhoea
• highly resistant

Question 11

What are the 3 main steps in germination?

Answer 11

• 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

Question 12

How does C Diff carry out cell adhesion?

Answer 12

• 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

Question 13

Where are toxin A and B encoded onto?

Answer 13

Pathogenicity Locus (PaLoc)

Question 14

What is the mechanism of action for Toxins A and B?

Answer 14

(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

Question 15

What are the complications of C.Diff?

Answer 15

Bloody diarrhoea
constipation

Question 16

What symptoms occur when tight junctions are weakened and why do they occur?

Answer 16

• diarrhoea and inflammation: toxins, bacteria leak through the gut lining due to toxins A and B inactivating Rho proteins

Question 17

What are the key features of C Difficile ribotype 027?

Answer 17

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

Question 18

What are the complications of a C.Diff infection?

Answer 18

toxic megacolon: severe inflammation and dilation of the colon

Question 19

How would you diagnose C Difficile associated Diarrhoea?

Answer 19

• clinical sample: faeces (glutamate dehydrogenase)
• antigen detection is initial screening test
• non culture techniques: toxin detection, selective agar and ribotyping

Question 20

What are the 2 ways of carrying out toxin detection?

Answer 20

1) Enzyme immunoassay for toxin a and b in stool - rapid but not sensitive
2) pcr detecting toxin B in stool

Question 21

What are the types of lab tests we do for C Diff?

Answer 21

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

Question 22

What are some treatments for C Diff?

Answer 22

• oral antibiotics: vancomycin and fidaxomicin
  replacement fluid and electrolytes
• discontinuing precipitating antibiotics
• biotherapy: aims to restore gut microbiome

Question 23

How can C Diff be prevented?

Answer 23

using narrow spectrum antibiotics
isolating patients
eliminating spores from the environment