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MoD > L13 - Normal microbiota > Flashcards

L13 - Normal microbiota Flashcards

1
Q

What does symbiosis mean?

A

Two or more organisms co-exist in close physical association

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2
Q

What are the 4 types of symbiosis?

A
  • mutualism
  • neutralism
  • commensalism
  • parasitism
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3
Q

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

A

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

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4
Q

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

A

Neither organism derives benefit nor harm

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5
Q

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

A

One organism benefits, the other derives neither benefit nor harm

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6
Q

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

A

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

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7
Q

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

A

The host derives harm

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

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8
Q

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

A
  1. by surface cleaning
  2. by barriers
  3. by physical separation
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9
Q

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

A

Lower respiratory tract (cilia in lungs etc)

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10
Q

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

A
  • upper genital tract (cervix)
  • urinary tract (urethra)
  • middle ear (eustachian tube)
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11
Q

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

A
  • pleural cavity
  • peritoneal cavity
  • spinal cord and meninges
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12
Q

What is tissue tropism?

A

Propensity for a particular organism to grow in a particular habitat

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13
Q

Which bacteria live on the skin? (skin flora)

A
  • coagulase-negative staphylococci (staphylococcus epidermis)
  • staphylococcus aureus (esp. in nasal carriers)
  • propionibacterium species (propionibacterium acnes)
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14
Q

Which bacteria live in the mouth? (mouth flora)

A
  • viridans/oral streptococci
  • anaerobes
  • many others
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15
Q

Which bacteria live in the nostrils?

A
  • skin flora

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

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16
Q

Which bacteria live in the pharynx?

A

Respiratory and other pathogens

  • strep. pyogenes (group A)
  • haemophilus influenzae
  • strep. pneumoniae
  • neisseria meningitidis
  • staph. aureus
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17
Q

Which bacteria live in the vagina pre-puberty?

A
  • skin flora

- lower GI flora (mainly E. coli)

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18
Q

What causes the change in vagina flora post-puberty?

A

Glycogen produced due to circulating oestrogens

  • Lactobacillus acidophilus
    ferments glycogen resulting in very acidic pH killing normal flora
19
Q

Which bacteria live in the vagina post-puberty?

A
  • lactobacillus spp. Lactobacillus acidophilus
  • skin flora
  • a few C. albicans
20
Q

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

A

Ferments glycogen

Maintains pH at 3, preventing overgrowth of other species

21
Q

There is an association between H. pylori and which conditions?

A

duodenal and gastric ulceration

22
Q

What inhibits bacterial growth in the stomach?

A

Low gastric pH due to hydrochloric acid

23
Q

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

A

AEROBIC

few or no anaerobes

24
Q

Which bacteria live in the stomach and small intestine?

A
  • acid-tolerant lactobacilli

- helicobacter pylori

25
Q

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

A

95-99% ANaerobic

26
Q

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

A
  • Bacteriodes spp. Clostridium spp. Bifidobacteria spp
27
Q

Which aerobic bacteria live in the large intestine?

A

Enteric gram-negative bacilli

  • escherichia coli
  • klebsiella spp. enterobacter spp. proteus spp. citrobacter spp.
28
Q

How many microorganisms are in the large intestine?

A

10 to power 9 - 10 to power 11 organisms/gram

at least 400 species identified

29
Q

What are the benefits of having normal flora?

A
  • metabolism
  • colonisation resistance
  • induction of cross-reactive antibodies (may have a protective effect)
30
Q

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

A
  • vitamins K and B12 are secreted by enteric bacteria
31
Q

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

A
  • environmental manipulation eg. lowering pH

- antibacterial agents eg .colicins, bacteriocins, fatty acids, metabolic waste products

32
Q

What is the main risk factor for clostridium difficile infection?

A

Antibiotic treatment

33
Q

What are the symptoms of Clostridium difficile infection?

A
  • diarrhoea

- pseudomembranous colitis

34
Q

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

A

Faecal transplants

35
Q

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

A
  • multiple sclerosis
  • chronic fatigue syndrome (ME)
  • idiopathic thrombotic purpura
  • ulcerative colitis
  • irritabel bowel syndrome
  • diabetes mellitus
36
Q

When does normal flora become problematic?

A
  • overgrowth
  • translocation
  • cross-infection
37
Q

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

A

Presence at the wrong site

  • spread from one surface to another
  • inoculation into a normally sterile site
38
Q

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

A

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

39
Q

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

A

Conjunctivitis

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

40
Q

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

A

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

41
Q

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

A

MRSA

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

42
Q

Give a list of conditions caused by normal flora

A
  • dental caries, periodontal disease, pharyngitis
  • abscesses
  • endocarditis
  • pneumonia
  • gastroenteritis, peritonitis
  • urogenital infections
43
Q

what is the most common aerobic bacteria in the large intestine?

A

Escherichia coli

44
Q

do healthier people have a less or more diverse range of flora?

A

more diverse

MoD (19 decks)

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