Gut Flora

Question 1

What is microbiota?

Answer 1

Normal flora.

Question 2

What is tissue tropism?

Answer 2

Tissue tropism is the ability of a pathogen to infect a particular tissue.

Question 3

What are fimbriae?

Answer 3

Appendages that can be found on many Gram-negative and some Gram-positive bacteria that is thinner and shorter than a flagellum used for attachment to surfaces.

Question 4

How does the number of bacteria change with distance from the stomach?

Answer 4

Flora increase in numbers with distance from the stomach.

Question 5

Which flora are present throughout from the stomach to the colon?

Answer 5

Gram-positive flora.

Question 6

Which flora are only present from the ileum onwards?

Answer 6

1 - Anaerobes.

2 - Coliforms.

Question 7

What is the difference between gram positive and gram negative bacteria?

Answer 7

• Gram positive bacteria have a thick, multi-layered peptidoglycan wall, whereas gram negative have a thin, single-layered one.
• Gram positive bacteria have no outer membrane, whereas gram negative bacteria do.
• Gram positive bacteria retain crystal violet dye and stain purple. Gram negative bacteria need a counter stain to stain red or pink.

Question 8

What counterstains might be used to stain gram negative bacteria?

Answer 8

Safranin or fuschine.

Question 9

List 3 defences the pharynx has against harmful microorganisms.

Answer 9

1 - Flow of liquids.

2 - Lysozymes.

3 - Normal flora.

Question 10

List 2 defences the oesophagus has against harmful microorganisms.

Answer 10

1 - Peristalsis.

2 - Flow of liquids.

Question 11

What defence does the stomach have against harmful microorganisms?

Answer 11

Low pH.

Question 12

List 6 defences the small intestine has against harmful bacteria.

Answer 12

1 - Peristalsis.

2 - Flow of liquids.

3 - Shedding of epithelium.

4 - Peyer’s patches (ileum).

5 - IgA.

6 - Mucus.

Question 13

What are Peyer’s patches?

Answer 13

Masses of lymphatic tissue found throughout the ileum of the small intestine.

Question 14

What is a glycoalyx?

Answer 14

A pericellular matrix made of a glycoprotein and glycolipid covering that surrounds the cell membranes of some bacteria.

Question 15

How do salivary glands defend against harmful microorganisms?

Answer 15

• They secrete a buffered neutral pH solution that neutralises bacterial acids.
• They secrete lysozymes that attack bacterial peptidoglycan.

Question 16

How do microbiota help make the environment unfavourable for exogenous bacteria?

Answer 16

Their metabolic byproducts contribute to this environment.

Question 17

What can cause polymicrobial mediastinitis?

Answer 17

• Ccan be caused by perforation of the oesophagus.

- Inflammation of the mediastinum due to microbial infection.

Question 18

How might liver cirrhosis cause microbial infection of the peritoneum?

Answer 18

• In liver cirrhosis, portal hypertension occurs.
• Instead of being cleared from the liver, bacteria in the portal vein enter peri-hepatic lymphatics.
• From there, they reach the peritoneum.

Question 19

What are diverticula?

Answer 19

Herniations of the mucosa and submucosa through the outer muscle layer of the larger intestine, causing pouches to form.

Question 20

List 3 relatively antibiotic resistant bacteria that might replace normal flora after using antibiotics.

Answer 20

1 - Enterobacter.

2 - Pseudomonas spp.

3 - Candida albicans.

Question 21

Where can Campylobacter spp be found?

What can result from hosting it?

Answer 21

• It is part of the normal flora of the chicken intestine.

- Consuming an undercooked contaminated chicken carcass can result in gastroenteritis.

Question 22

Where can Escherichia coli be found?

How is it transmitted?

Answer 22

• It is a part of the normal flora of farm animals.

- Transmitted via touch.

Question 23

List 3 syndromes and diseases caused by Escherichia coli.

Answer 23

1 - Haemorrhagic colitis.

2 - Haemolytic uraemic syndrome.

3 - Renal failure.

Question 24

In which environment can Clostridium difficile proliferate?

Answer 24

Where normal flora are absent due to antibiotics.

Question 25

What toxins does Clostridium difficile release?

• What do these toxins do to the GIT?

Answer 25

• B cytotoxin.
• A enterotoxin.
• These toxins damage enterocytes.

Question 26

List 7 infections that may be caused by normal flora.

Answer 26

1 - Abscesses.

2 - Pharyngitis.

3 - Sepsis (inflammatory immune response).

4 - Endocarditis.

5 - Pneumonia.

6 - Gastroenteritis.

7 - Urogenital infections.

Question 27

Give an example of a cause of appendicitis.

Answer 27

If a faecolith obstructs the lumen of the appendix, normal flora can reproduce behing the faecolith.

Question 28

List 2 bacteria that can cause liver abscesses.

Answer 28

1 - Enterococcus spp.

2 - Streptococcus spp.

Question 29

List 2 major bacteria of the jejunum.

Answer 29

1 - Enterococci.

2 - Lactobacilli.