10. Normal microbiota

Question 1

What does symbiosis mean?

Answer 1

Two or more organisms co-exist in close physical association

Question 2

Symbiosis is when 2 or more organisms co-exist in close physical association. What are the 4 types of symbiosis?

Answer 2

• mutualism
• neutralism
• commensalism
• parasitism

Question 3

Mutualism is a type of symbiosis. What does it mean?

Answer 3

Both organism benefit from symbiosis (benefit from co-existing in close physical association)

Question 4

Neutralism is a type of symbiosis. What does it mean?

Answer 4

Neither organism derives benefit nor harm

Question 5

Commensalism is a type of symbiosis. What does it mean?

Answer 5

One organism benefits, the other derives neither benefit nor harm

Question 6

Parasitism is a type of symbiosis. What does it mean?

Answer 6

One organism (parasite) benefits at the expense of the other (host)

Question 7

In parasitic symbiosis, does the host organism benefit or derive harm?

Answer 7

The host derives harm

It is the parasite that benefits at the expense of the host

Question 8

In sterile sites of the body, sterility is maintained by 3 mechanisms. What are these?

Answer 8

1. by surface cleaning (open to the environment)
2. by barriers that allow unidirectional flow (adjacent to non-sterile sites)
3. by physical separation from non-sterile sites (closed cavities)

Question 9

Give an example of a sterile site in the body where sterility is maintained by surface cleaning

Answer 9

Lower respiratory tract (lungs etc)

Question 10

Give examples of sterile sites in the body where sterility is maintained by barriers that allow unidirectional flow

Answer 10

• upper genital tract (cervix)
• urinary tract (urethra)
• middle ear (eustachian tube)

Question 11

Give examples of sterile sites in the body where sterility is maintained by physical separation from non-sterile sites?

Answer 11

• pleural cavity
• peritoneal cavity
• spinal cord and meninges

Question 12

What is tissue tropism?

Answer 12

Propensity for a particular organism to grow in a particular habitat

Question 13

Which bacteria live on the skin? (skin flora)

Answer 13

• coagulase-negative staphylococci (staphylococcus epidermis)
• staphylococcus aureus (esp. in nasal carriers)
• propionibacterium species (propionibacterium acnes)

Question 14

Which bacteria live in the mouth? (mouth flora)

Answer 14

• viridans/oral streptococci
• anaerobes
• many others

Question 15

Which bacteria live in the nostrils?

Answer 15

• skin flora

- staph. aureus (20% - nose is main carrier site)

Question 16

Which bacteria live in the pharynx?

Answer 16

Respiratory and other pathogens

• strep. pyogenes (group A)
• haemophilus influenzae
• strep. pneumoniae
• neisseria meningitidis
• staph. aureus

Question 17

Which bacteria live in the vagina pre-puberty?

Answer 17

• skin flora

- lower GI flora (mainly E. coli)

Question 18

What causes the change in vagina flora post-puberty?

Answer 18

Glycogen produced due to circulating oestrogens

Question 19

Which bacteria live in the vagina post-puberty?

Answer 19

• lactobacillus spp. Lactobacillus acidophilus
• skin flora
• a few C. albicans

Question 20

In the vagina post-puberty, there is lactobacillus acidophilus. What does this do?

Answer 20

Ferments glycogen

Maintains pH at 3, preventing overgrowth of other species

Question 21

There is a link between H. pylori and which condition?

Answer 21

Gastric ulcer

Question 22

What inhibits bacterial growth in the stomach?

Answer 22

Low gastric pH

Question 23

The flora of the stomach and small intestine is predominantly aerobic or anaerobic bacteria?

Answer 23

AEROBIC

few or no anaerobes

Question 24

Which bacteria live in the stomach and small intestine?

Answer 24

• acid-tolerant lactobacilli

- helicobacter pylori

Question 25

The flora of the large intestine is predominantly aerobic or anaerobic?

Answer 25

95-99% ANaerobic

Question 26

Which anaerobic (95-99%) bacteria live in the large intestine?

Answer 26

- Bacteriodes spp. Clostridium spp. Bifidobacteria spp

Question 27

Which aerobic bacteria live in the large intestine?

Answer 27

Enteric gram-negative bacilli - escherichia coli - klebsiella spp. enterobacter spp. proteus spp. citrobacter spp.

Question 28

How many microorganisms are in the large intestine?

Answer 28

10 to power 9 - 10 to power 11 organisms/gram at least 400 species identified

Question 29

What are the benefits of having normal flora?

Answer 29

- synthesis and excretion of vitamins - colonisation resistance - induction of cross-reactive antibodies (may have a protective effect)

Question 30

Synthesis and excretion of vitamins is a benefit of having normal flora. Give examples

Answer 30

- vitamins K and B12 are secreted by enteric bacteria

Question 31

Colonisation resistance is a benefit of having normal flora. Give examples

Answer 31

- environmental manipulation eg. lowering pH | - antibacterial agents eg .colicins, bacteriocins, fatty acids, metabolic waste products

Question 32

What is the main risk factor for clostridium difficile infection?

Answer 32

Antibiotic treatment

Question 33

What are the symptoms of Clostridium difficile infection?

Answer 33

- diarrhoea | - pseudomembranous colitis

Question 34

What treatment has recently made a comeback to treat recurrent C. diff infection?

Answer 34

Faecal transplants

Question 35

What other diseases is it suggested that faecal transplants may be a possible treatment for?

Answer 35

- multiple sclerosis - chronic fatigue syndrome (ME) - idiopathic thrombotic purpura - ulcerative colitis - irritabel bowel syndrome - diabetes mellitus

Question 36

What are some examples of pathology of normal flora?

Answer 36

- overgrowth - translocation - cross-infection

Question 37

Translocation is a possible pathology of normal flora. What does this mean?

Answer 37

Presence at the wrong site - spread from one surface to another - inoculation into a normally sterile site

Question 38

Give an example of a condition that can be caused by overgrowth of normal flora?

Answer 38

Vaginal thrush eg. - treatment with broad spectrum antibiotics for sinusitis causing inhibition of colonisation resistance - vaginal itch with creamy vaginal discharge

Question 39

Give an example of a condition that can be caused by translocation (from one surface to another) of normal flora

Answer 39

Conjunctivitis eg. - red eyes and purulent conjunctival discharge following URTI with cough and runny nose - haemophilus influenzae grown from eye swabs

Question 40

Give an example of a condition that can be caused by translocation (inoculation into a normally sterile site) of normal flora

Answer 40

Intravascular catheter infection eg. - post bowel resection due to Chrohn's - spiking fevers - associated with intravenous drug use - blood culture grew coagulase-negative staphylococci - problem resolved immediately after central line removed

Question 41

Give an example of a condition that can be caused by cross-infection of normal flora

Answer 41

MRSA eg. - severe pancreatitis - develops pneumonia - MRSA grown from respiratory secretions - died despite appropriate antibiotics - MRSA isolated in nose swabs from 4 other patients

Question 42

Give a list of conditions caused by normal flora

Answer 42

- dental caries, periodontal disease, pharyngitis - abscesses - endocarditis - pneumonia - gastroenteritis, peritonitis - urogenital infections