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Gastrointestinal pathophysiology > Microbiology of the gut > Flashcards

Microbiology of the gut Flashcards

1
Q

GI infections can be non-inflammatory, inflammatory or penetrating. Give the mechanism, location and example of bacteria which are involved in the non-inflammatory pathway

A
  1. Mechanism: Produces enterotoxins which adhere to the mucosa and alter it, by opening porins or directly damaging the intracellular lining of the bowel
  2. Location: Proximal small bowel
  3. Exambles: Vibrio cholerae, bacillus cereus, Enterotoxigenic E.coli (VTEC)
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2
Q

GI infections can be non-inflammatory, inflammatory or penetrating. Give the mechanism, location and example of bacteria which are involved in the inflammatory pathway

A
  1. Mechanism: Invasion of mucosa/production of cytotoxins
  2. Location: Colon
  3. Examples: Shigella spp., salmonella spp, Campylobacter jejuni, Enterohaemorrhagic/enteroinvasive E.coli, C.diff
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3
Q

GI infections can be non-inflammatory, inflammatory or penetrating. Give the mechanism, location and example of bacteria which are involved in the penetrating pathway

A
  1. Mechanism: Attach to receptors on enterocyte and induce the cell to phagocytose the organism into the cytoplasm.
  2. Location: Distal small bowel
  3. Examples: Salmonella typhi, Yersinia enterocolitica, Listeria monocytogenes
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4
Q

Verotoxigenic E.coli (VTEC) is an example of non-inflammatory causes of GI infections. What is the clinical manifestation of this?

A
  1. Diarrhoea
  2. Dysentry (bloody diarrhoea) following damage, death and ulceration of GI mucosa
  3. Cause haemolytic uraemic syndrome (HUS) if it gets into the blood
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5
Q

Dysentry is more common in which age range vs HUS?

A 
Dystenry = elderly
HUS = children
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6
Q

VTEC is 2-3x more likely to cause HUS if the child has been given what?

A

An antibiotic

- This is why giving an antibiotic is usually bad until you are certain of what is going on

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7
Q

Why do you not nurse a group of patients with diarrhoea?

A

Because each one could have different bacterial causes

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8
Q

Even though gastroenteritis is gone when your symptoms go, why do some occupations require proof that the organism has gone before you can go back to work? (such as the food industry)

A

The bacteria can remain colonised for long periods after recovery, such as salmonella

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9
Q

How can you get intermittent peristalsis from gastroenteritis? How can this be helped?

A

Because gastroenteritis, specifically campylobacter-caused, can cause damage to the nerve plexi which travel through the bowel
- This can be helped by a high fibre diet as it is the easiest thing to travel through the bowels

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10
Q

How long do symptoms of gastroenteritis last, norovirus (viral) vs campylobacter (bacteria)?

A

Norovirus - around 3 days

Campylobacter - around 3 weeks

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11
Q

Give some host defences against GI infection

A
  1. Gastric pH
  2. Bile salts/acids
  3. Peristalsis
  4. Mucus
  5. Immunity
  6. GALT
  7. Normal flora of the GI tract
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12
Q

How does gastric pH act as a host defence against infection?

A
  • It is good at digesting food but also at killing microorganisms
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13
Q

How does gastric pH act as a host defence against infection?

A
  • It is good at digesting food but also at killing microorganisms
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14
Q

How do bile salts/acids act as a host defence against GI infection?

A
  • Good at emulsifying fats so we can digest them but also good at digesting and emulsifying the cell membrane of bacteria and all bacteria of the cell membrane underneath the cell wall
  • This makes them very effective at sterilising the contents of the bowel in the upper small intestine
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15
Q

How does peristalsis act as a host defence against GI infection?

A

Keeps the contents of the bowel moving through
- If it was slowed, then bacteria could have time to get in, multiply, produce toxins, damage the cell wall of the enterocytes and cause infection

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16
Q

How does mucus act as a host defence against GI infection?

A

Lines over the enterocytes, it is more porous but still a difficult environment for bacteria to survive in
- it holds chemicals like lysozyme which can digest the capsules of organisms

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17
Q

How does the immune system in the bowel act as a defence against GI infection?

A

The IgA antibody in the bowel is the most important
- Secretory IgA is stuck to the enterocytes and to specific immune cells where the secretory IgA is released from the mucosal surface, these oxidise bacteria and work for APCs

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18
Q

What is GALT?

A

Sometimes the immune system in the bowel is called GALT, it is highly specialised

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19
Q

What are Peyer’s patches?

A

Essentially lymph nodes but along the bowel, there is a lot of immune tissue in the bowel and a lot of action is needed to keep you from constantly being infected by something

20
Q

How does the regional (normal) flora of the GI tract act as a host defence against infection?

A

An infecting organism is infecting a space already heavily colonised with highly adapted bacteria, so it must compete which is a challenge
- The floral bacteria use nutrients, physically attach to receptors and also produce anti-biotic like substances called bacteriocins

21
Q

Regional GI flora are mostly found where?

A
  1. Colon

- There are small numbers in the stomach, duodenum and jejunum

22
Q

How does the appendix act as a host defence against GI infection?

A
  1. It is full of GALT/MALT so it is essentially a lymphoid tissue
    - It is a normal store of flora from your bowel
23
Q

How does the appendix offer an advantage against cholera?

A

Cholera causes such severe diarrhoea that it can wash out the entire bowel flora, so you can be left with C.diff or yeast or bacterial overgrowth syndromes.
- The people who suffered most from this were affluent people who could afford to have their appendix removed

24
Q

Give some of the roles of the microbiome

A
  1. Synergistic
  2. Synthetic: biotin, folate
  3. Release of nutrients: Fe, Ca, amino acids
  4. Remove toxins e.g. heterocyclic amines from cooking
  5. Compete out pathogens
  6. Release energy: carbohydrates to sugars
25
Q

If flora leaks out of the bowel, what can this cause?

A
  1. Peritonitis

2. UTI

26
Q

C.diff causes which type of gastroenteritis?

A

Inflammatory

27
Q

When C.diff damages and reduces the bowel flora, what will be present which can hatch, colonise and cause infection?

A

C.diff spores

28
Q

What are symptoms of C.diff gastroenteritis?

A
  1. Mild diarrhoea
  2. Fever
  3. > inflammatory markers
  4. Extreme end = toxic megacolon or malnutrition
29
Q

Which symptoms of gastroenteritis mean that it is probably not C.diff caused?

A
  1. Rash
  2. Bloody diarrhoea
  3. Vomiting
30
Q

What is toxic megacolon?

A

When the nerve plexus through the colon is paralysed, the bowel vessels are stretched flat so the bowel becomes ischaemic

  • The immune system stops working and the organisms translocate across, and you become septicaemic very quickly
  • Whole process of death from septic shock takes 3-6hrs
31
Q

Antibiotics which lead to C.diff infection?

A

4C’s

  1. Clindamycin
  2. Cephalosporins
  3. Ciprofloxacin
  4. Co-amoxiclav
32
Q

C.diff usually affects which people?

A

Elderly, infirm patients, esp. those in hospital/nursing homes

33
Q

Classical appearance of the mucosa with C.diff infection

A

Pseudomembranous colitis

  • Cobblestone appearance of mucosa
  • White spots are areas of mucosal damage and death
34
Q

Pathogenesis of C.diff infection?

A

Production of mucosa-damaging toxins A and B

35
Q

Diagnosis of C.diff infection?

A
  1. Toxin detection = ELISA & then PCR
36
Q

Management of C.diff infection?

A
  1. Stop inciting antibiotics
  2. Isolate patients
  3. Specific anti-C.diff antimicrobials
    - Oral metronidazole
    - Oral vancomycin
    - Oral fidaxomicin
    - FOR 10-14 days
  4. Faecal flora transport
37
Q

In the small intestine, the majority of organisms are gram …

A

POSITIVE

38
Q

If the large bowel flora starts to wash back into the small intestine, what happens?

A

Bacterial overgrowth

39
Q

What happens when there is bacterial overgrowth?

A

The organisms in the bowel will chemically alter the bowel contents, such as deconjugating bowel acids, causing fat malabsorption (steatorrhoea)
- Deconjugated bile acids also inhibit carbohydrate transport, causing osmotic diarrhoea which lowers pH, causing further fat malabsorption

  • The organisms will also try to eat the contents of the SI which we want to absorb, such as Fe, B12, Ca, Vit A, selenium, protein etc..
40
Q

What are the clinical consequences of bacterial overgrowth in the bowel?

A
  1. Diarrhoea
  2. Bloating
  3. Abdo pain
  4. Flatulence
  5. Steatorrhoea
  6. Weight loss
  7. Microcytic anaemia (Fe)
  8. Macrocytic anaemia (B12/folate)
  9. Tetany (Ca)
  10. Visual acuity (Vit A)
  11. Dermatitis (selenium)
  12. Rosacea
  13. Wt loss/cachexia (protein)
41
Q

Diagnostic test for bacterial overgrowth?

A

Hydrogen breath test

42
Q

Treatment for bacterial overgrowth?

A

Treat underlying condition

RIFAXAMIN

43
Q

Gut flora associated diseases

A

Autism - C.boltiae

Asthma/atopy - < bifidobacteria and > clostridia

Obesity - < bacteroides and > actinobacteria

44
Q

What are prebiotics?

A

Food that we put into our bowel, they affect our microbiome and consequently our health
- These substances come from types of carbs (mostly fibre) that humans cant digest but the beneficial bacteria in your gut can eat this fibre

45
Q

What are probiotics?

A

These are live bacteria found in certain foods or supplements which provide numerous health benefits

  • Direct effects on invading pathogens
  • Indirect by stimulating immune function e.g. sIgA production

Gastrointestinal pathophysiology (22 decks)

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