Microbiology of GI Tract

Question 1

What types of flora are there?

Answer 1

→Resident flora - for life,commensal organisms

→Transient flora - temporarily reduced - carried or changes

Question 2

Why do the color and texture of babies feces change a lot?

Answer 2

→change in organisms of the baby’s gut

Question 3

What do the organisms from a babys gut change from and to?

Answer 3

→facultative anaerobes to obligate anaerobes

Question 4

What does bifidobacter produce and what does it prevent?

Answer 4

→produces lactic acid
→prevents the growth of gram negative bacteria
→Metabolise breast milk sugars

Question 5

Once a baby starts to wean what happens to the bifidobacter?

Answer 5

→bifdobacter decreases and becomes

→bacteroides, clostridia and eubacteria

Question 6

How many bacteria are there in the stomach?

Answer 6

→There are few bacteria due to the acidic conditions

Question 7

When do the bacteria increase?

Answer 7

→ As you go into the jejunum and duodenum

→ Mainly lactobacillus

Question 8

What are the obligate anaerobes?

Answer 8

→bacteroides
→ bifidobacter
→clostridia

Question 9

What are facultative anaerobes?

Answer 9

→E.Coli

Question 10

What kind of bacteria is E.Coli?

Answer 10

→gram negative

Question 11

How many bacteria per gram are there in feces?

Answer 11

→10x11 bacteria per gram

→ 1:1 ratio

Question 12

Going from the top to the bottom of the GI how do bacteria change?

Answer 12

→number and complexity of the species increases.

Question 13

What two types of bacteria does a normal gut usually have?

Answer 13

→bacteroides

→firmicutes

Question 14

What diseases are associated with microbiome alterations?

Answer 14

→Crohn’s disease
→Inflammatory bowel disease
→Clostridium difficile
→Colon cancer
→Allergy
→Celiac disease
→Diabetes type I and II
→Obesity (bacteroidetes/firmicute ratios)
→Mental health and depression

Question 15

How do scientists find bacteria in the gut?

Answer 15

→targeting and sequencing 16S rRNA is how scientists find the bacteria in the gut.

Question 16

What are the host defences against pathogens?

Answer 16

→Structural
Seamless epithelium, tight junctions, sloughing/turnover
→Mechanical
Peristalsis, chewing, fluid movement
→Biochemical
Gastric acid, bile, mucus
→Immunological
Secretory IgA, intraepithelial lymphocytes

Question 17

What are the 4 benefits of gut flora?

Answer 17

→Colonization resistance - blocks pathogens
→Metabolites of benefit to host
→Normal development of immunity
→Aids digestion

Question 18

How do gut flora produce gut metabolites?

Answer 18

→Vitamin K, B12, organic acids
→Enhanced utilization of amino acids
→Butyrate for colonocytes - maintain anerobiasis

Question 19

How do gut flora aid digestion?

Answer 19

→Fermentation of sugars (10% of energy), H2 or methane, regulation of fat storage

Question 20

What do probiotic organisms produce?

Answer 20

→lactic acid and organic acids

Question 21

What do probiotic organisms do?

Answer 21

→get 10% absorbable energy from dietary fibre.

Question 22

What is the function of microbial antagonism?

Answer 22

→Maintains flora through complex interactions - competition between flora
→Limits the growth of competitors and pathogens

Question 23

How does gut flora prevent colonization?

Answer 23

→Bacteriocins (peptides that kill other bacteria)
→Reduced numbers of available epithelial receptors
→Keeps pH low
→Controls oxidative potential
→Limits pathogen growth
→Occupy all niches
→High numbers
Waste products

Question 24

What does loss of flora lead to?

Answer 24

→ Bacterial or pathogen overgrowth

Question 25

What effects does ciprofloxacin have on flora and when does this return to normal?

Answer 25

→decrease in diversity with significant effects on 1/3rd of taxa
→ returns to normal in 4 weeks

Question 26

What is diarrhoea defined as?

Answer 26

→Defined as watery or liquid stools

→Increase in stool weight above 200g per day

Question 27

What are clinical consequences of diarrhoea?

Answer 27

→Can lead to severe dehydration
→Excessive fluid and electrolyte loss
→Hypovolaemia, hypokalaemia
→Organ failure
→Long term morbidity and reduced growth

Question 28

What is the global impact of diarrhoea?

Answer 28

→3 billion episodes per year

→1.3 million deaths per year due to dehydration

Question 29

What are the organisms that cause diarrhoea?

Answer 29

→Microorganisms
→Bacteria
→Viruses
→Parasites - protozoal and worms
→Shed in feces and transmission to new hosts

Question 30

What is dysentery and what is it associated with?

Answer 30

→Inflammatory disorder of GI tract - usually large intestine

→Often associated with blood and pus

Question 31

What are the symptoms of dysentery?

Answer 31

→Pain
→ fever
→abdominal cramps

Question 32

Acute of chronic diarrhoea + blood + pus = ?

Answer 32

= dysentery

Question 33

What does chronic diarrhoea or malabsorption lead to?

Answer 33

→ steatorrhea

→ fat malabsorption

Question 34

What does infective proctitis lead to?

Answer 34

→ ano-rectal STIs

Question 35

What is associated with dyspepsia?

Answer 35

→ ulcers

→ H. pYlori

Question 36

What is associated with dysphagia?

Answer 36

→oesophagus

→ candida

Question 37

What are the 4 types of damage caused by GI infection?

Answer 37

→Pharmacological action of bacterial toxins
→Local inflammation in response to superficial microbial invasion
→Deep invasion to blood and lymphatics and dissemination of the organism to other body sites
→Perforation/ ulceration of mucosal epithelium
Peritonitis, intra abdominal abscess

Question 38

What causes watery diarrhoea?

Answer 38

→ epithelial cells/enterocytes are damaged
→ absorption of fluid is stopped
→villi are damaged
→ crypt cells start hypersecreting

Question 39

What do E.Coli toxins do?

Answer 39

→toxin migrates into the cell and causes changes to cAMP
→change protein kinases
→change chloride channels

Question 40

How does changing chloride channels by E.Coli cause diarrhoea

Answer 40

→There is hyperchloride secretion

→Causes the osmotic flow of water following the chloride and fluid is secreted leading to diarrhoea.

Question 41

How does EPEC E.COli work?

Answer 41

→Enteropathogenic E.Coli binds to the brush border and the microvillus structure is destroyed so the enterocytes no longer works.
→ Adherence

Question 42

How do viruses cause diarrhoea?

Answer 42

→Viruses can penetrate the enterocytes which destroy the cells.
→No absorption occurs and malabsorption happens with hypersecretion.
→There is villus atrophy and as a result of this you get crypt hyperplasia, eventually the villi recover.

Question 43

What are the 3 mechanisms of diarrhoea and what organisms cause this?

Answer 43

→ Bacterial toxins - E.coli
→ Adherence - E.coli
→ Penetration and iNvasion - Viruses

Question 44

What is the microbiome affected by?

Answer 44

→diet
→ antibiotics
→surgery
→genes