DERS 09 - GIT Infections 4

Question 1

What is an intra-abdominal abscess and what is the usual cause?

Answer 1

A collection of pus within the abdomen usually caused by the extension of an infection or inflammation from an appendicitis, diverticulitis, or pancreatitis

Question 2

What are the only enospore forming bacteria families we need to know?

Answer 2

Bacillus

Clostridia

Question 3

What pathogen is the most common cause of intraabdominal abscesses?

Answer 3

Bacteroides fragilis

Question 4

Answer the following about B. fragilis:

• Gram status
• Aerobic or anaeriobic
• Normal GI flora?

Answer 4

• Gram negative
• Anaerobic
• Normal flora of large intestine

Question 5

List the B. fragilis virulence factors and what they do

Answer 5

• Fimbriae for adhsion
• LPS for adhesion, not toxic
• Polysaccharide capsule triggers host response to wall off the bacteria and form an abscess
• Beta lactamases

Question 6

Answer the following about Clostridium difficile:

• Gram status
• Shape
• Aerobic or anaerobic

Answer 6

Gram +ve bacillus

obligate anaerobe

Question 7

What are the clinical features of C. difficile

Answer 7

Can be as mild as no symptoms are as severe as toxic megacolon. Usual symptoms are:

• 3 loose water stools per day
• Anorexia
• Nausea
• Leukocytosis (neutrophilic)

Question 8

List the risk factors for developing a C. difficile infection

Answer 8

• Clindamycin (highest risk), penicillins, aminoglycosides (lowest risk)
• >65yo
• Prior hospitalization or a lengthy hospitalization

Question 9

List the C. difficile virulence factors and what they do

Answer 9

• Exotoxins, TcdA & TcdB, which transfer glucose onto GTPases (inactivating them) involved in cytoskeleton regulation, leading to cell death
• Flagella
• Adhesins

Question 10

Why is disruption of GI flora so important for establising a C. difficile infection?

Answer 10

C. difficile requires a primary bile acid that the normal gut flora metabolizes

Question 11

How is C. difficile diagnosed?

Answer 11

• Clinical symptoms and risk factors
• Diagnotic tests
  
  • NAAT (nucleic acid amplification test) - takes a few hours and is very sensitive and specific but doesnt identify active toxin production
  • EIA for GDH antigen - usually just for initial screening, requires confirmatory testing
  • EIA for toxins A and B - must detect both

Question 12

List the timing classifications for diarrhea

Answer 12

• Acute is <2 weeks
• Persistent is 2-4 weeks
• Chronic is >4 weeks

Question 13

What are the signs of non inflammatory and inflammatory diarrhea? What are the usual pathogeneses. What are the usual causes?

Answer 13

• Non inflammatory diarrhea
  
  • Watery and non-bloody
  • Mucosal hypersecretion/malabsorption without mucosal destruction; usually in SI
  • Typically caused by viruses and non-invasive bacteria
• Inflammatory diarrhea
  
  • blood/pus diarrhea and a fever
  • Mucosal invasion with inflammation; usually the LI
  • Typically caused by invasive or toxin producing bacteria