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Year 2 EMS MoD > Normal microbiota > Flashcards

Normal microbiota Flashcards

1
Q

How many microbial cells does a normal human body contain?

A

10^14.

-10 times the number of human cells

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2
Q

Where in the body is the density of microorganisms greatest?

A

Oral cavities and colon (10^10).

-moist areas

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3
Q

What is normal flora?

A

Organisms found in/on the body that don’t cause disease.

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4
Q

What is symbiosis?

A

Two or more organisms co-existing in close physical association.
-e.g. human host and normal flora

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5
Q

What are the different types of symbiosis? (4)

A
  • Mutualism
  • Neutralism
  • Commensalism
  • Parasitism
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6
Q

What is mutualism?

A

Both organisms benefit from symbiosis.

-e.g. N-fixing bacteria

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7
Q

What is neutralism?

A

Neither organism derives benefit or harm.

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8
Q

What is commensalism?

A

One organism benefits, the other derives neither benefit nor harm.

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9
Q

What is parasitism?

A

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

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10
Q

What is the difference between sterile and non-sterile sites?

A

Non-sterile sites have normal flora, sterile sites have no normal flora.

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11
Q

What is a feature of non-sterile sites?

A

They are exposed to the environment (directly/indirectly).

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12
Q

When does the acquisition of normal flora begin?

A

At birth.

-sterility is maintained until birth

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13
Q

Give some examples of non-sterile sites.

A

Skin
Nasopharynx
GI tract
Vagina

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14
Q

What is the difference between the flora present in babies who are breast fed and bottle fed?

A

BREAST-FED; mainly bifidobacteria and lactobacillus.

BOTTLE-FED; more enterobacteriacea.

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15
Q

How is sterility maintained at sterile sites?

A
  • SURFACE CLEANING (open to environment)
  • BARRIERS that allow unidirectional flow (next to non-sterile sites)
  • PHYSICAL SEPARATION (cavities)
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16
Q

Give an example of a sterile site maintained by surface cleaning.

A

Lower respiratory tract.

  • cleaning by ciliated epithelium
  • bacteria removed by coughing/sneezing
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17
Q

Give an example of a sterile site maintained by barriers that allow unidirectional flow.

A
  • Upper genital tract (cervix)
  • Urinary tract (urethra)
  • Middle ear (auditory tube)
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18
Q

Give an example of a sterile site maintained by physical separation.

A
  • Plural cavity
  • Peritoneal cavity
  • Spinal cord and meninges
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19
Q

What are microenvironments?

A

Different sites within sites.

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20
Q

What is tissue tropism?

A

How well a particular organism grows in a particular habitat.

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21
Q

How does H. pylori survive in the stomach?

A

In releases ammonia to increase the pH.

22
Q

What sort of bacteria tend to colonise moist areas?

A

Gram -ve.

23
Q

Where are most bacteria located on the skin?

A

In sweat glands.

24
Q

What is a big difference between the environments of the skin and the gingival crevice (space between tooth and gum)?

A
  • Skin has variable temperature, and is an aerobic, dry and nutrient-poor environment
  • Gigival crevice has a constant temperature and is an anaerobic, moist and nutrient-rich environment
25
Q

What bacteria make up the skin flora? (3)

A
  • Staphylococcus epidermis
  • Staphylococcus aureus
  • Propionibacterium acnes
26
Q

What bacteria make up the mouth flora? (2)

A
  • Viridans/oral streptococci

- Anaerobes

27
Q

How are mouth flora beneficial?

A

Synthesise essential vitamins.

28
Q

What bacteria make up the nasopharyngeal flora?

A

NOSTRILS - S. aureus

PHARYNX - streptococcus pyogenes, haemophilus influenzae, Streptococcus pneumoniae, etc

29
Q

What bacteria make up vaginal flora pre-puberty?

A
  • Skin flora

- Lower GI flora (mainly E. coli)

30
Q

What bacteria make up vaginal flora post-puberty?

A
  • Lactobacillus spp
  • Skin flora
  • Some Candida albicans
31
Q

Why does the composition of vaginal flora change after puberty?

A

Glycogen is produced due to circulating oestrogens.

-Lactobacillus spp. ferment glycogen to maintain pH

32
Q

Why is a low pH in the vagina beneficial?

A

Prevents infection by opportunistic pathogens.

-e.g. C. albicans overgrowth

33
Q

What is an opportunistic infection?

A

An infection caused by pathogens that take advantage of a host with a weakened immune system or altered microbiota.

34
Q

What feature of the stomach helps to inhibits bacterial growth?

A

Low gastric pH.

35
Q

What organisms are found in the stomach and small intestine? (2)

A

Predominantly aerobic bacteria:
-Lactobacilli (acid-tolerant)
-H. pylori
Increase in numbers distally

36
Q

How did Barry Marshall prove that there is a link between H. pylori and stomach ulcers?

A

Drank cultures of H. pylori&raquo_space; stomach ulcer.

37
Q

How can H. pylori survive in very acidic environments?

A

Produces urease&raquo_space; convert urea to ammonia and CO2.

38
Q

What proportion of the population is H pylori present in?

A

30-50%.

39
Q

How many organisms are present in the large intestine?

A

10^10 organism/gram.

-400+ species

40
Q

What proportion of the species in the large intestine are anaerobes?

A

95-99%.

  • Clotridium spp
  • Bacteriodes spp.
41
Q

Which aerobic bacteria are present in the large intestine?

A

Enteric gram -ve bacilli.

-E coli, Enterobacter, etc

42
Q

What prevents overgrowth of pathogens in the large intestine?

A

Colonisation resistance by normal gut microflora.

43
Q

What are the main benefits of normal flora?

A
  • Synthesis of vitamins (e.g. K and B12 by enteric bacteria)
  • Colonisation resistance
  • Induction of cross-reactive antibodies
44
Q

What does E coli produce in the colon?

A

Vitamin K.

-essential for blood clotting, bone metabolism

45
Q

What are the main methods of colonisation resistance?

A
  • Environment manipulation (e.g. decrease pH)

- Antibacterial agents (e.g. FAs, bacteriocins)

46
Q

What is the main risk factor for C. difficile?

A

Antibiotic treatment.

  • disruption of normal flora&raquo_space; bacteria overgrowth
  • HCAI
47
Q

What are faecal transplants used to treat?

A

C. difficile.

  • increases the diversity of microfora
  • better recovery than just vancomycin
48
Q

How can normal flora lead to disease? (3)

A
  • Overgrowth
  • Translocation
  • Cross-infection
49
Q

How does translocation of normal flora lead to disease?

A

Presence at the wrong site.

-e.g. conjunctivitis; H. influenzae in eye

50
Q

Give an example of a disease caused by overgrowth of normal flora.

A

Vaginal thrush.

-often due to broad spectrum antibiotics

51
Q

Give an example of a disease caused by cross-infection of normal flora.

A

MRSA.

52
Q

What proportion of normal flora is culturable?

A

1%.

Year 2 EMS MoD (20 decks)

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