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Medical Sciences > MICROBIOME AND PATHOGENESIS > Flashcards

MICROBIOME AND PATHOGENESIS Flashcards

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USMLE® Step 1 flashcards
1
Q

Microbiota

A

An individuals microbes, vary between site and individuals

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2
Q

Normal flora

A

Microbiota

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3
Q

Microbiome

A

Microbes and aggregate of microbial genomes in the microbiota

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4
Q

Core microbiome

A

Commonly shared species at a specific site

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5
Q

Secondary microbiome

A

Species that contribute to diversity in an individual

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6
Q

Describe gut microbiota

A

Highest number of organisms in bodily niche

Seeded at birth - affected by child delivery option

Rapidly diversified

Typical adult profile within first few years of life

Common phyla include Firmicutes and Bacteroidetes

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7
Q

What are roles of the microbiome?

A

Digestion, producing vitamins and minerals

Protect against pathogens

Regulate immune system

Possibly contribute to mood and behaviour

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8
Q

Structure of a virus

A

Lack cytoplasm

Proteins synthesised on host ribosomes

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9
Q

Describe prokaryotes structure

A

Lack cytoskeleton

Shape determined by cell wall

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10
Q

Describe eukaryotes structure

A

Cytoskeleton
Complex internal structure
Arches like information processing
Bacteria like metabolism

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11
Q

Describe archaea structure

A

Ether linked membrane lipids

Unique metabolic features

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12
Q

Describe bacteria structure

A

Eater linked membrane lipids

Peptidoglycan cell wall

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13
Q

Describe the cell wall

A

Main load bearing structure

Resists osmotic pressure and determines cell shape

Peptidoglycan (Murien) - polysaccharide chains with peptide cross links

Signal to innate immune system of bacterial presence

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14
Q

Describe the gram positive bacteria cell wall

A

Thick cell wall made up of many layers of murein.

Several constituents (teichoic acids, lipoteichoic acids and protein) protrude from this layer

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15
Q

Describe the structure of the gram negative bacterial cell wall

A

Thin cell wall and outer membrane

Outer leaflet of the outer membrane is made up of lipopolysaccharide

Space between the 2 membranes is the periplasm.

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16
Q

Describe peptidoglycan structure

A

Alternating N-acetylglucosamine and N-acetyl-muramic acid

Peptide cross links attached to NAM residues

It is thick (20-25 layers) in gram positive bacteria

It is thin (1-3 layers) in gram negative bacteria

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17
Q

What is the peptidoglycan arrangement in gram positive bacteria?

A

It was previously assumed that it would be in multiple layers but now evidence exists that it is wound into cables which are wrapped around the cell

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18
Q

Describes the peptidoglycan arrangement in gram negative rods

A

Polysaccharide chains wrapped around the circumference of cell, peptide cross links parallel to cell axis

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19
Q

Describe the cell membrane

A

It is a phospholipid bilayer

It is the main permeability barrier

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20
Q

Describe capsules

A

Amorphous polysaccharide slime surrounding cell

Presence and composition strain - specific

Environment - prevents desiccation

In animal hosts : inhibits phagocytosis

Attachment to surfaces

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21
Q

Describe the structure and function of flagella

A

Generate thrust by rotation at 200-1000 rpm

Attached via hook and basal body containing motor proteins (driven by proton gradient) and switch proteins (control direction of rotation)

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22
Q

Describe pili and fimbriae

A

Protein spikes used to attach to surfaces

Type 1 fimbriae required for pathogenic Escherichia Coli strains to adhere to urethra to cause UTI

Sex Loki involved in DNA transfer in conjugation

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23
Q

What are the 4 basic viral forms

A

Icosahedral nucleocapsid

Enveloped icosahedron

Helical, non enveloped

Helical, enveloped

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24
Q

Describe the structures in a icosahedral nucleocapsid virus

A

Capsomeres (proteins)

Nucleic acid

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25
Q

Describe the structures in an enveloped icosahedron virus

A

Nucleic acid

Envelope consists of phospholipid and glycoproteins

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26
Q

Describe the structures of the helical non enveloped virus

A

Nucleic acid

Proteins

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27
Q

Describe the structures in the helical enveloped virus

A

Nucleic acid

Envelope: phospholipid and glycoprotein

28
Q

How are virus’ classified?

A

By the presence/absence of the envelope

By The type of nucleic acid present is the Baltimore classification

29
Q

What are the viral forms?

A

RNA viruses

DNA viruses

30
Q

Describe the viral lifecycle

A

Attachment and entry to host

Uncoating

Replication

Assembly and maturation

Released by budding

31
Q

What is commensalism?

A

One of the 2 organisms in a relationship benefits. The other doesn’t gain and isn’t harmed

32
Q

What is mutualism?

A

Both partners in a relationship gain

33
Q

What is parasitism?

A

Where one organism in the relationship gains at the expense of the other

34
Q

What is a pathogen?

A

Organisms or infectious agents which cause disease

35
Q

Pathogenesis

A

The mechanism by which a disease is produced

36
Q

Pathogenicity

A

Ability of an organism to cause disease

37
Q

Virulence

A

The relative ability of a pathogen to cause disease

38
Q

Infection

A

Invasion of microorganisms into a host

39
Q

Infectivity

A

The ability of a microbe to enter, survive in and multiply in a susceptible host

40
Q

Infectious disease

A

When infection leads to host damage and injury

41
Q

Epidemic

A

Unusually high number of cases at a particular time

E.g. plague

42
Q

Endemic

A

Always present

E.g. gonorrhoea

43
Q

Pandemic

A

Worldwide

E.g. influenza

44
Q

Acute

A

Quick

E.g. measles

45
Q

Chronic

A

Slow

E.g. tuberculosis

46
Q

Specific

A

E.g. smallpox

47
Q

Non-specific

A

E.g. wound infection

48
Q

What is the chain of infection

A

Characteristics of the organism (pathogen)

Portal of entry

Reservoir

Portal of Exit

Mode of transmission

Characteristics of the host

49
Q

What are characteristics of the organism (pathogen)?

A 
Type 
Ability to invade host 
Virulence 
Degree to which it causes disease 
Number of organisms
50
Q

What are possible portals of entry

A 
Eyes
Mucous membranes 
Respiratory tract 
Placenta 
Breaks in host barriers
51
Q

What are possible reservoirs?

A

Humans
Animals
Environmental surfaces

52
Q

What are possible portals of exit?

A 
Respiratory tract 
Genitourinary tract 
Gastrointestinal tract 
Skin/mucosal surfaces
Placenta 
Blood
53
Q

What are possible modes of transmission?

A

Direct contact
Droplets
Vectors
Airborne

54
Q

What are possible characteristics of the host?

A

Lack of effective resistance
Changes in host defences
Tissues destruction

55
Q

What are possible sources of infection?

A

Endogenous:
- from the host itself

Exogenous:

  • from people (cases, carriers)
  • from animals (zoonoses) e.g. plague from rabies
  • from the environment e.g. legionella from water, tetanus from soil
56
Q

What are the possible routes of spreading infection through horizontal transmission?

A

To other people:

  • airborne e.g. influenza, colds, TB
  • faecal-oral e.g. food poisoning, typhoid
  • sexual contact e.g. gonorrhoea, HIV
  • vectors e.g. mosquitos carry malaria
  • animals e.g. rabies

Indirect transmission:
-fomites

57
Q

What are the possible ways of spreading infection through vertical transmission?

A

Mother to child e.g. HIV, rubella

58
Q

What are possible virulence factors?

A 
Adhesins 
Bacterial toxins - exotoxins and endotoxins 
Invasiveness
Cell damage 
Avoid immune response
59
Q

Describe exotoxins

A

May be the principal cause of disease

Proteins produced by gram positive and gram negative bacteria

Many consist of a number of subunits

Secreted into the extracellular space

Differing modes of action - cytotoxic, enterotoxic, neurotoxic

60
Q

Describe clostridium and clostridial neurotoxins

A

Anaerobic, spore forming organisms

Ubiquitous in the environment

Very potent molecules

Affect peripheral nervous system

Clostridium botulinum causes botulism. It produces one of seven toxins - A B C D E F G (BoNT/A and so on)

Clostridium tetani causes tetanus (lockjaw). It produces one toxin - TeNT

61
Q

Describe tetanus

A

Can be neonatal and maternal

Results from wound infection

Causes muscle rigidity and spasm

62
Q

Describe botulism

A

Caused by food poisoning - ingestion of pre formed toxin
Caused by wounds - introduction of spores
Infant botulism can occur

Causes descending flaccid paralysis
In babies it results in a failure to feed

63
Q

Describe the structure of a neurotoxin

A

It is a tripartite toxin - it has 3 parts:

The protease which is the active subunit
The translocation unit
The binding domain

64
Q

How does botulism result in flaccid paralysis?

A

The BoNTs act at the neuromuscular junction

65
Q

How does tetanus cause muscle spasms and then paralysis?

A

TeNT enters at the neuromuscular junction and is transported to the spinal cord where it acts within inhibitory interneurons

66
Q

What are possible toxin modifications?

A

Chimera - results in binding to different target cells
Delivery vehicle - causes inactivated protease. Carry drugs or other molecules into cells
Non paralytic - enters central neurone

Medical Sciences (9 decks)

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