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EMS - MoD > 11./12. Microorganisms in disease > Flashcards

11./12. Microorganisms in disease Flashcards

1
Q

What are the general stages in the chain of infection?

A
  • pathogenic organism
  • reservoir
  • exit
  • transmission
  • entry
  • susceptible host
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2
Q

What is virulence?

A

May be used interchangeably to describe pathogenicity

Virulence is sometimes defined as the degree to which a micro-organism is able to cause disease

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3
Q

Staphylococcus aureus and streptococcus viridans are both pathogenic. Which is more virulent?

A

Staph. aureus is more virulent than strep. viridans, as it causes disease much more readily

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4
Q

Briefly, what are the 4 main Koch’s postulates? (1890)

A
  • organism should be present in disease but not in health
  • organism should be isolated from diseased animal and grown in pure culture
  • organism should cause the same disease in a newly inoculated animal
  • organism should be re-isolated from the experimentally-infected animal
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5
Q

What are the main routes of transmission?

A
  • faecal-oral
  • blood-borne
  • respiratory
  • direct contact (hand-hand, mucous membranes)
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6
Q

What does LD50 mean?

A

Lethal dose

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7
Q

What does ID50 mean?

A

Infectious dose

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8
Q

What does infectivity mean?

A

The ability of a microorganism to become established on/in a host

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9
Q

Infectivity is the ability of a microorganism to become established in/on a host. How can this occur?

A
  • microbial ligand

- host cell surface receptor

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10
Q

Give some examples of ligand-receptor interactions

A
  • E. coli P fimbriae: glycolipids on human uroepithelial cells (tiny hair-like structures that express specific adhesins)
  • S. pyogenes protein-F: fibronectin1 (large multifunctional glycoprotein found in connective tissue, on cell surfaces, and in various body fluids)
  • influenza haemagglutinin: respiratory epithelial sialic acid receptors
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11
Q

What are virulence factors?

A

Components of microorganisms that result in harmful effects

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12
Q

Give some examples of virulence mechanisms

A
  • facilitation of adhesion
  • toxic effect(s)
  • tissue damage
  • interference with host defence mechanisms
  • facilitation of invasion
  • modulation of the host cytokine responses
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13
Q

What are virulence factors sometimes referred to as?

A
  • adhesins
  • aggressins
  • interferins
  • modulins
    etc
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14
Q

An endotoxin is a type of what?

A

Virulence factor

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15
Q

Are endotoxins release from the live or dead bacterial cell?

A

Endotoxins are released from damaged/dead cells

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16
Q

Where are endotoxins found?

A

They are a component of the gram-negative bacterial cell wall

  • E.coli and other gram-negative bacilli
  • Neisseria meningitidis
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17
Q

Which class of bacteria possess endotoxins?

A

Gram-negative bacteria

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18
Q

What is the active component of endotoxins?

A

Lipopolysaccharide (LPS)

the term LPS often used interchangeably with endotoxin

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19
Q

What do endotoxins do?

A

Binds to a number of host cell receptors

Induces a range of uncontrolled host responses

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20
Q

Strictly speaking, what is a lipopolysaccharide?

A

Any polysaccharide containing lipid

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21
Q

A host response to an endotoxin is SIRS - systemic inflammatory response syndrome. What is involved in this?

A
  • uncontrolled T-lymphocyte response
  • uncontrolled activation of the clotting cascade
  • uncontrolled activation of complement
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22
Q

One of the components of SIRS is uncontrolled T-lymphocyte response. What is involved in this?

A
  • cytokine release: TNF-a, y-interferon, interleukin-1
  • fever, rigors, hypotension, tachycardia, collapse
  • cardiac and/or renal failure
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23
Q

One of the components of SIRS is uncontrolled activation of the clotting cascade. What is involved in this?

A
  • disseminated intravascular coagulation (DIC)
  • depletion of clotting factors
  • bleeding tendency
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24
Q

SIRS (systemic inflammatory response syndrome) encompasses imprecise terms such as what?

A

Septic shock and endotoxic shock

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25
Q

What is Waterhouse-Friedrichsen syndrome?

A

An example of the catastrophic effects of endotoxin

Meningococcal infection results in bilateral adrenal haemorrhage and subsequent adrenal failure, largely due to endotoxin release from Neisseria meningitidis

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26
Q

Give a consequence of Neisseria meningitidis infection?

A

Endotoxin-mediated increase in vascular permeability causes loss of protein, fluid and plasma into the tissues, with pathological compensatory vasoconstriction

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27
Q

Exotoxins are types of what?

A

Virulence factors

28
Q

What are exotoxins? What are they produced by?

A

Proteins produced by living bacteria

29
Q

Do exotoxins have broad or specific effects?

A

Exotoxins usually have quite specific effect(s) on the host

30
Q

What is botulism caused by?

A

Exotoxins produced by clostridium botulinum (obligate anaerobe)

The toxins block the nerve impulse from getting to the muscles at the neuromuscular junction

31
Q

How is botulism caused?

A
  • ingestion of pre-formed toxin (contaminated food)
  • infection of dirty wounds (may be trivial wounds)
  • gastrointestinal colonisation (infants)
32
Q

What are the general symptoms of botulism?

A
  • double vision
  • drooping eyelids
  • sore throat
  • flaccid paralysis
  • respiratory failure
33
Q

What is the clinical presentation of botulism (in medical terms)? Hint:5 Ds

A
  • diplopia
  • dysphagia
  • dysarthria
  • dry mouth
  • death (from respiratory failure)
34
Q

At which sites do botulism toxins act?

A

At the neuromuscular junction

35
Q

What causes tetanus?

A

The toxin released by clostridium tetani (obligate anaerobe)

36
Q

How is tetanus caused?

A
  • infection of dirty wounds (may be trivial wounds)
  • toxin production
  • death caused by respiratory paralysis
37
Q

What is the tetanus toxin caused?

A

Tetanospasmin

38
Q

What are the effects of tetanospasmin (the tetanus toxin)?

A
  • produced on germination of spores
  • binds to nerve synapses
  • inhibits release of inhibitory neurotransmitters (eg. gamma-amino butyric acid) in the central nervous system
39
Q

Ultimately, how is death caused in tetanus?

A

Death is caused by respiratory paralysis

40
Q

What does obligate anaerobe mean?

A

Means they are poisoned by oxygen

41
Q

What are the main symptoms of tetanus?

A
  • jaw stiffness (lockjaw)
  • muscle spasms
  • fever
  • sweating
  • tachycardia

Developing into muscle rigidity and respiratory failure

42
Q

As well as botulism and tetanus, give some other exotoxin-mediated infections

A
  • cholera (vibrio cholerae)
  • diphtheria (corynebacterium diphtheriae)
  • clostridium difficile infection (causing diarrhoea and colitis)
  • E. coli O157 haemorrhagic colitis (verotoxin)
  • staphylococcal scalded skin syndrome (Staph. aureus)
  • whooping cough/pertussis (bordetella pertussis)
  • scarlet fever (strep. pyogenes)
  • scalded-skin syndrome (staph. aureus epidermolysin)
43
Q

What do streptococcus pyogenes virulence factors do?

A

They promote connective tissue breakdown and invasion

44
Q

Give some streptococcus pyogenes syndromes

A
  • streptococcal sore throat
  • erysipelas
  • necrotising fasciitis
  • scarlet fever
45
Q

What are the streptococcus pyogenes virulence factors?

A
  • hyaluronidase and streptokinase
  • C5a peptidase
  • streptolysins -O and -H
  • erythrogenic toxin (phage-encoded)
  • toxic shock syndrome toxin
46
Q

Hyaluronidase and streptokinase are virulence factors of S. pyogenes. What do they do?

A

Break down connective tissue components - facilitate tissue invasion

47
Q

C5a peptidase is a virulence factor of S. pyogenes. What does it do?

A

Inactivates complement component C5a

48
Q

Streptolysins -O and -H are virulence factors of S. pyogenes. What do they do?

A

Lyse red and white blood cells and platelets

49
Q

Erythrogenic toxin (phage-encoded) is a virulence factor of S. pyogenes. What does it do?

A

Causes the rash of scarlet fever

50
Q

Toxic shock syndrome toxin is a virulence factor of S. pyogenes. What does it do?

A

Streptococcal toxic shock syndrome is superficially similar to a syndrome of endotoxin release

51
Q

What is responsible for the rash in scarlet fever?

A

The erythrogenic toxin (phage-encoded) produced by S. pyogenes

52
Q

In what ways do pathogens evade the immune system?

A
  • inhibition of phagocytosis

- intracellular pathogens

53
Q

How does S. pyogenes inhibit phagocytosis?

A

M-protein binds fibrinogen and masks bacterial surface, blocking complement binding and opsonisation

54
Q

How does S. pneumoniae inhibit phagocytosis?

A

Polysaccharide capsule inhibits opsonisation and therefore phagocytosis

55
Q

Give some intracellular pathogens (helps immune evasion)

A
  • myobacterium tuberculosis
  • salmonella typhi
  • listeria monocytogenes
56
Q

What are the 2/3 components that viruses consist of?

A
  • genome (RNA or DNA)
  • capsid (protein)
  • (envelope - lipid bilayer)
57
Q

Viruses are incapable of what?

A

Independent existence

58
Q

What do viruses use to satisfy the requirements of growth and replication?

A

Host mechanisms

59
Q

What are the stages in the generic virus life cycle?

A
  1. adsorption
  2. penetration
  3. uncoating
  4. synthesis
  5. assembly
  6. release
60
Q

Adsorption is the first stage in the virus life cycle. What is this?

A

Interaction between host receptor molecule and virus ligand (determines host-specificity of the virus)

61
Q

Penetration is the second stage in the virus life cycle. What is this?

A

Receptor-mediated endocytosis or, in some enveloped viruses, membrane fusion

62
Q

Uncoating is the third stage in the virus life cycle. What is this?

A

Nucleic acid is liberated from the phagosome (if endocytosed) and/or capsid by complex enzymatic and/or receptor-mediated processes

63
Q

Synthesis is the fourth stage in the virus life cycle. What is this?

A

Nucleic acid and protein synthesis are mediated by host and/or viral enzymes. These take place in nucleus or cytoplasm, depending on the specific virus

64
Q

Assembly is the fifth stage in the virus life cycle. What is this?

A

Assembly of virus components is mediated by host and/or viral enzymes

65
Q

Release is the sixth stage in the virus life cycle. What is this?

A

Complete virus particles are released by budding off host cell membrane or disintegration of host cell

66
Q

What is endocytosis?

A

A form of active transport in which a cell transports molecules into the cell by engulfing them in an energy-using process

EMS - MoD (17 decks)

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