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Yr 2 - EMS > Normal Microbiota > Flashcards

Normal Microbiota Flashcards

1
Q

Where is organism density the greatest?

A

In the oral cavities and colon

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2
Q

What are normal flora / normal microbiota?

A

Organisms found in a given location in a state of health

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3
Q

What is colonisation?

A

Establishment at a site in the body

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4
Q

What are microbiota?

A

All the organisms in a given community

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5
Q

What is microbiome?

A

All the genes present within the microbiota

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6
Q

What is symbiosis?

A

Two or more organisms co-exist in close physical association

E.g. Relationship between human ‘host’ and the normal flora often described as symbiotic.

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7
Q

Regarding symbiosis, what does ‘mutualism’ mean?

A

Both organisms benefit from symbiosis

E.g. Nitrogen fixing bacteria and legumes

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8
Q

Regarding symbiosis, what does ‘neutralism’ mean?

A

Neither organism derives benefit or harm

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9
Q

Regarding symbiosis, what does ‘commensalism’ mean?

A

One organism benefits, the other derives neither benefit nor harm

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10
Q

Regarding symbiosis, what does ‘parasitism’ mean?

A

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

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11
Q

Does normal flora exist in non-sterile sites? In sterile sites?

A

Non-sterile sites have normal flora

Sterile sites have no normal flora

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12
Q

What are the non-sterile sites of the human body?

A
  1. Skin
  2. Conjunctiva
  3. Nasopharynx
  4. Vagina
  5. GI tract
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13
Q

When does the acquisition of normal flora begin?

A

Until birth, sterility is maintained throughout. The acquisition of normal flora begins at birth

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14
Q

How can blood cultures/CSF/pleural fluid become potentially contaminated?

A

Obtained by passing a needle through the skin into the relevant ‘sterile’ site. Potential for contamination with skin organisms.

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15
Q

How can a sputum sample become potentially contaminated?

A

Obtained by expectoration of lower airways secretions (‘sterile site’) through the upper airway (‘non-sterile site’) – risk of contamination

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16
Q

How can a urine sample become potentially contaminated?

A

Obtained by passing urine from the bladder/upper urinary tract (‘sterile site’) via the terminal urethra (‘non-sterile site’).

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17
Q

How is risk of contamination in a urine sample reduced?

A

Risk of contamination reduced by collecting Mid Stream Urine (MSU) sample

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18
Q

How is sterility of the lower respiratory tract maintained?

A

Maintained by surface cleaning –> cilia

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19
Q

What are the 3 ways that sterility in the body can be maintained?

A
  1. Surface cleaning
  2. Barriers
  3. Physical separation creating closed cavities
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20
Q

How do barriers maintain sterility?

A

Allows uni-directional flow (adjacent to non-sterile sites)

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21
Q

What are examples of places where sterility is maintained by barriers?

A
  • Upper genital tract protected by cervix

- Urinary tract protected by urethra

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22
Q

What are examples of places where sterility is maintained by physical separation from non-sterile sites?

A

Pleural cavity, peritoneal cavity, spinal cord and meninges

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23
Q

What is tissue tropism?

A

A propensity for a particular organism to grow in a particular habitat

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24
Q

What physical variables influence where organisms will grow?

A 
Moisture
Temperature
pH
O2 availability
Nature of surface
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25
Q

What is a gingival (gum) crevice?

A

A narrow space between the free margin of the gingival (gum) epithelium and the adjacent enamel of a tooth

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26
Q

Describe the characteristics of a gingival crevice

A
  • Constant temperature
  • Moist
  • Few physical challenges (toothbrush)
  • Anaerobic environment
  • Bathed in nutrients
  • Mucosal surface components
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27
Q

What bacteria are commonly found in mouth flora?

A
  • Viridans / oral streptococci
28
Q

What is a common organism found in the nasopharyngeal flora?

A

S. aureus

29
Q

What pathogens can the pharynx support the growth of?

A
  • Streptococcus pyogenes (group A)
  • Haemophilus influenzae
  • Streptococcus pneumoniae
  • Neisseria meningitidis
  • S. aureus
30
Q

What happens if the respiratory tract epithelium becomes damaged?

A

These species can cause infections in the lower respiratory tract.
E.g. Bronchitis, pneumonia

31
Q

How does flora in vagina change?

A

Changes due to puberty

32
Q

Describe vaginal flora pre-puberty

A
  • Skin flora

- Lower GI flora (mainly E.coli)

33
Q

What causes a change to vaginal flora post-puberty?

A

Glycogen produced due to circulating oestrogens –> change of mucosal tract

34
Q

What bacteria does the presence of glycogen in vaginal flora post-puberty cause the colonisation of?

A
  • Lactobacillus spp. Lactobacillus acidophilus
  • Skin flora
  • A few C. albicans
35
Q

What is function of Lactobacillus spp. Lactobacillus acidophilus?

A
  • Ferment glycogen

- Help maintain low pH of about 3 to prevent overgrowth of other species

36
Q

What is purpose of low pH kept by vaginal flora?

A

Prevents overgrowth of other species (preventing infection)

37
Q

What is purpose of low pH of stomach?

A

Inhibits bacterial growth

38
Q

What bacteria are found in the stomach?

A

Predominantly aerobic bacteria:

  • acid-tolerant Lactobacilli
  • Helicobacter pylori
39
Q

What can Helicobacter pylori cause?

A

Stomach ulcers/acute gastritis

40
Q

How can Helicobacter pylori survive the highly acidic nature of the stomach?

A

H. pylori secretes an enzyme called urease, which converts the chemical urea to ammonia. The production of ammonia around H. pylori neutralises the acidity of the stomach, making it more hospitable for the bacterium

41
Q

What bacteria is found in the large intestine?

A
  • 95-99% anaerobes

- Aerobic bacteria

42
Q

What type of anaerobes are found in the large intestine?

A

Bacteroides spp., Clostridium spp. Bifidobacteria spp

43
Q

What type of aerobic bacteria are found in the large intestine?

A

Enteric Gram-negative bacilli (e.g. E. coli)

44
Q

How does normal flora benefit metabolism?

A

Synthesis of secondary metabolites/vitamins

E.g:

  • Vitamins K and B12 secreted by enteric bacteria
  • Fermenting unused energy substrates (SCFA)
45
Q

How does normal flora benefit colonisation resistance?

A

Environmental resistance

E.g:

  • Low pH
  • Antibacterial agents (e.g. fatty acids, colicins)
46
Q

How does normal flora benefit the immune system?

A

Induction of cross-reactive antibodies (may have a protective effect)

47
Q

What does oral microbiota produce?

A

Nitric Oxide

48
Q

What is the benefit of oral microbiota producing nitric oxide?

A

Essential for vascular health

49
Q

What product can negatively affect nitric oxide produced by oral microbiota?

A

Mouthwash

50
Q

What are 3 examples of intestinal short chain fatty acids?

A
  1. Acetate
  2. Butyrate
  3. Propionate
51
Q

How do intestinal short chain fatty acids benefit the gut?

A
  • Helps to inhibit enteropathogens
  • Provides energy to epithelial cells / colonocytes
  • Promotes mucin production.
  • Affects gut hormone production – modulates appetite
52
Q

What is a diverse range of microbiota related to?

A

Health (poor diversity may be linked to obesity)

53
Q

What is ‘clostridium difficile’ infection? What is the main risk factor?

A

Hospital acquired infection

Main risk factor is antibiotic treatment

54
Q

How can antibiotic treatment lead to ‘clostridium difficile’ infection?

A

Perturbation of normal colonic microflora allows C. difficile overgrowth

Leads to toxin production which interacts with mucosal surface of large intestine

Causes diarrhoea and Pseudomembranous colitis

55
Q

How is microbiota of the gut affected in Crohn’s disease?

A

Patients with IBD have a strongly diminished diversity of the gut microbiota

56
Q

What may infant antibiotic use increase your risk of?

A

Adult obesity

57
Q

What is a faecal transplant?

A

The transfer of stool from a healthy donor into the gastrointestinal tract for the purpose of treating recurrent C. difficile colitis.

58
Q

What is overgrowth of normal flora?

A

Excessive growth at normal site

E.g. vaginal thrush

59
Q

What is translocation of normal flora?

A

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

60
Q

How can broad spectrum antibiotics affect normal flora?

A

Can lead to inhibition of colonisation resistance

Can often lead to candida infections

61
Q

How can translocation of normal flora lead to conjunctivitis?

A

Haemophilus influenzae (following URTI with cough and runny nose) being translocated to the eyes (e.g. after rubbing eyes)

62
Q

How can an intravascular catheter lead to translocation of normal flora?

A

Coagulase-negative staphylococci usually found on skin can colonise the central line and cause infection

63
Q

What is MRSA?

A

Meticillin-resistant S. aureus (MRSA).

This is a type of bacteria that is resistant to several antibiotics.

64
Q

Other clinical conditions caused by normal flora:

A
  • Abscesses
  • Pneumonia
  • Gastroenteritis, peritonitis
  • Endocarditis
  • Urogenital infections
  • Dental caries, peridontal disease, pharyngitis
65
Q

Why are clinical conditions caused by normal flora difficult to determine?

A

Opportunity for sample contamination high

Organism may be present benignly

Yr 2 - EMS (60 decks)

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