10 Normal microbiota

Question 1

How many microbial cells does the human body harbour?

Answer 1

10^14

10x the number of human cells

Question 2

Define normal flora and colonisation.

Answer 2

Normal flora: organisms food in a given location in a state of health.
Colonisation: establishment at a site in the body.

Question 3

Define neutralism.

Answer 3

Neither organism derives benefit or harm from the symbiosis.

Question 4

What is a non-sterile body site?

Which sites are they?

Answer 4

No mechanism to maintain sterility.

Conjunctiva, nasopharynx, GI tract, vagina, skin.

Question 5

How is sterility maintained in sterile sites? (3)

Name some examples.

Answer 5

Surface cleaning - LRT.
Barriers allowing uni-directional flow - cervix, urethra, eustachian tube.
Physical separation pleural + peritoneal cavity. Spinal cord + meninges.

Question 6

What is tissue tropism in regard to microbiology?

Answer 6

Propensity for a particular organism to grow in a particular habitat.

Question 7

What are the skin flora? (3)

Answer 7

Coagulase-negative staphylococci (staphylococcus epidermis).
Staphylococcus aureus.
Propionibacterium acnes.
Skin near any orifice may be similar to the orifice.

Question 8

Which micro-organisms are commonly mouth flora? (2)

Answer 8

Viridian’s/oral streptococci.

Anaerobes.

Question 9

What is the flora in the pharynx? (5)

Answer 9

Streptococcus pyogenes.
Haemophilus influenza.
Streptococcus pneumoniae.
Neisseria meningitidis.
S. aureus.

Question 10

What is the normal flora in the vagina?

How and to what does this change after puberty? (3)

Answer 10

Pre-puberty: skin, lower GI (E.coli).
Post: Glycogen present due to oestrogen. Lactobacillus acidophilus ferments glycogen, maintains pH 3. Skin flora + C. albicans.

Question 11

What is the normal flora in the stomach and small intestine?

Answer 11

Low pH inhibits growth.
Aerobes: acid-tolerant lactobacilli, H.pylori.
Counts increase distally.

Question 12

What is the normal flora of the large intestine? (8)

Answer 12

> 400 organisms.
95-99% anaerobes: Bacteroides, Clostridium, Bifidobacteria.
Aerobes: g-ve bacilli: Escherichia coli, Klebsiella, Enterobacter, Proteus, Citrobacter.

Question 13

What are the benefits of normal flora? (3)

Answer 13

Synthesis of vitamins K and B12.
Colonisation resistance by pH generation and antibacterial agents (collisions, bacteriocins, FAs etc).
Induction of cross-reactive antibodies.

Question 14

Which conditions is the micro biome thought to play a role in? (6)

Answer 14

IBDs.
Metabolic disorders.
Hypertension.
Obesity.
Cancer.
Infection (especially C.diff).

Question 15

What does C.diff infection lead to? (3)

Answer 15

Toxin production.
Diarrhoea.
Pseudomembranous colitis.

Question 16

Which diseases have faecal transplants been suggested for? (7)

Answer 16

C. diff (very effective).
MS.
Chronic fatigue syndrom.e
Idiopathic thrombotic purpura.
Ulcerative colitis.
IBS.
Diabetes mellitus.

Question 17

How may normal flora become pathological? (3)

Examples?

Answer 17

Overgrowth - thrush.
Translocation - conjunctivitis, intravenous catheter infection.
Cross-infection - MRSA.

Question 18

Which clinical conditions are commonly caused by normal flora? (6)

Answer 18

Abscesses.
Dental caries, periodontal disease, pharyngitis.
Pneumonia.
Endocarditis.
Gastroenteritis + peritonitis.
Urogenital infection.