Microbiology of the gut

Question 1

What is normal flora?

Answer 1

Microorganisms that live on all surfaces and within our gut

Question 2

What is Resident flora?

Answer 2

Microorganisms that are always present (for life)

Question 3

What is Transient Flora?

Answer 3

Microorganisms that colonise us but can temporarily be reduced, carried or changed according to various factors, including environmental

Question 4

Give an example of Example of a change in transient flora.

Answer 4

Bifidobacter
-metabolises breast milk sugars that gives gives itself energy and produces nutrients for the baby, also produces lactic acid and prevents growth of gram negative bacteria

as babies wean off breast milk, bifidobacter (gram positive) is switched to: bacteriocides (gram negative), clostridia and eubacteria

Question 5

Describe the Distribution and Frequency of Bacteria.

Answer 5

Few in stomach due to high acidity

more as we move through the duodenum and ileum and get to the terminal ileum

colon is an anaerobic environment and contains facultative and obligate anaerobes

Question 6

Describe the IBS effect on bacteria.

Answer 6

Distribution in the gut is very different in someone with IBS

Question 7

How is the microbiome of a part of the body investigated?

Answer 7

Through DNA extraction and sequencing of genes encoded in the bacterial genome that encodes for the rRNA.

Targetting 16S rRNA is now a way most studies investigate microbiome of any particular part of the body. Sequence is then compared to a database/reference to help classify organisms.

Question 8

What is Dysbiosis?

Answer 8

Microbial imbalance

Question 9

Describe the Structural Defence mechanisms of our gut.

Answer 9

Seamless epithelium surface with tight junctions, allowing for rapid turnover

Question 10

Describe the Mechanical Defence mechanisms of our gut.

Answer 10

Peristalsis moves things from oral to anal end

chewing and fluid movement prevents pathogens from adhering to epithelial cells as there is constant movement

Question 11

Describe the Biochemical Defence mechanisms of our gut.

Answer 11

Secretion of gastric acid, bile, mucus which kill bacteria as they are highly toxic to the microorganisms

Question 12

Describe the Immunological Defence mechanisms of our gut.

Answer 12

Secretory IgA at mucosal surfaces and intra-epithelial lymphocytes make sure there aren’t any adhering pathogens

Question 13

What has to happen first for a bacteria to cause infection?

Answer 13

Binding to epithelial cells

Question 14

Give some Benefits of commensal gut flora.

Answer 14

• Commensals have taken up ecological niches, therefore hard for pathogens to get in and start to divide and cause diseases
• Commensals produce metabolites useful for us e.g. Vit B12 and organic acids. Can also metabolise amino acids we can’t metabolise.
• Commensals produce butyrate for colonocytes which is a carbon source for these cells, maintaining anaerobic environment for colon
• Commensals important in normal immunological development to tolerate bacteria in the gut and not attack them
• Commensals aid in digestion and generate energy

Question 15

What are Probiotics?

Answer 15

Organisms that contribute to a healthy biome

best probiotic organisms produce lactic acid and organic acids e.g. lactobacillus

Question 16

Give some uses of probiotics.

Answer 16

to control diarrhoea in infants

to relieve constipation

to improve digestion of lactose

Question 17

What is Microbial Antagonism?

Answer 17

Competition between microbes

Question 18

Which antibiotic causes dysbiosis?

Answer 18

Ciprofloxacin

this allows for Clostridium difficile to overgrow and produce toxins that damage the gut and produce acute watery diarrhoea

overgrowth causes antibiotic associated colitis (pseudomembranous colitis)

Question 19

What is Dysentery?

Answer 19

Inflammatory disorder (infection) of the GI tract resulting in diarrhoea including blood and pus

Question 20

Describe the Damage done by Cholera Infection.

Answer 20

Disruption of fluid movemet across enterocyte membrane, leading to acute watery diarrhoea

Question 21

What is the Damage done by Shigella dysentery or campylobacter food poisoning?

Answer 21

Local inflammation

Question 22

What is the Damage done by Typhoid Fever or heptatitis A?

Answer 22

Deep invasion to blood and lymphatics and spreading of organism to other body sites

Question 23

What is the damage done by Entamoeaba histolytica?

Answer 23

Perforation/ulceration of mucosal epithelium, peritonitis or intra-abdominal abscess

Question 24

What is a Villus?

Answer 24

Fingerlike projection of the inner surface of the small intestine that functions in absorbing nutrients

Question 25

What are Crypts?

Answer 25

Tubular glands that lie between the intestinal villi and secrete intestinal juices into the small intestine

damage to enterocytes prevents absorption, causes hypersecretion of the crypts leading to acute watery diarrhoea

Question 26

How do bacterial toxins cause diarrhoea?

Answer 26

Enterotoxins affect the gut

Exotoxins affect fluid/electrolyte transport by increasing/decreasing cAMP

Cytotoxins produce direct cell damage to enterocytes causing hypersecretion of the crypts

Question 27

How does E.coli cause diarrhoea?

Answer 27

Binds to brush border and causes dysfunction of enterocytes and destruction of microvilli

results in anti-absorptive effects leading to acute water effects by stimulating Cl- channel (water follows by osmosis)

Question 28

What is Villus atrophy?

Answer 28

virus can penetrate into villi causing villus atrophy, causing for no absorptive capacity

results in crypt hyperplasia to try to replace the villus, causing lots of secretion