Microbial Virulence

Question 1

What are ‘indigenous biota’?

Answer 1

Micro-organisms that lie on our body surfaces, both internal and external, and are mainly bacteria

Question 2

What are indigenous biota constantly in?

Answer 2

Dynamic reflux

Question 3

What do normal clearing systems provide?

Answer 3

A semi-sterile environment in the upper GI tract and lower respiratory tract

Question 4

What is the importance of the bodys clearing system?

Answer 4

Although normal microbiota have low pathogenic potential, any change can lead to mild to life threatening endogenous infection

Question 5

What is the principle reserve for our microbiota?

Answer 5

The GI tract

Question 6

What may breaches of the GI tract lead to?

Answer 6

Heavy soiling of normally sterile sites

Question 7

What does virulence refer to?

Answer 7

The relative capacity of a microbe to cause damage to a host

Question 8

What can the concept of virulence occupy?

Answer 8

The full spectrum of non-pathogenic to highly pathogenic, which can result in life-threatening conditions

Question 9

Is there variety in virulence between strains of pathogens?

Answer 9

Yes

Question 10

What causes variety in virulence between strains of pathogens?

Answer 10

Changes in virulence factor repertoire and mobile genomic content

Question 11

Give an example of a pathogen that has variety in virulence between its strains?

Answer 11

S Aureus

Question 12

What is a pathogen defined as?

Answer 12

A microbe capable of causing host cell damage

Question 13

What can pathogens be categorised into?

Answer 13

• Obligate pathogen
• Typical pathogen
• Opportunistic pathogen

Question 14

Where are obligate pathogens found?

Answer 14

Only in humans associated with disease

Question 15

Give an example of an obligate pathogen

Answer 15

Mycobacterium tuberculosis

Question 16

What is meant by a typical pathogen?

Answer 16

Can be present as part of the normal biota, yet frequently cause disease

Question 17

Give an example of a typical pathogen

Answer 17

H. Influenzae

Question 18

Where is an opportunistic pathogen seen?

Answer 18

Only in immunocompromised patients, breaches of normal defences, or congential defects

Question 19

Give an example of an opportunistic pathogen?

Answer 19

S. Epidermidis

Question 20

What are the two main ways in which an individual will encounter a pathogen?

Answer 20

• Endogenous
• Exogenous

Question 21

What happens in endogenous infections?

Answer 21

The normal microbiota can multiply and develop

Question 22

What are endogenous infections due to?

Answer 22

Disruption of normal defences

Question 23

What happens in exogenous infections?

Answer 23

Infecting bacteria have been acquired from an external source, and is not part of the natural microbiota

Question 24

Where can pathogens come from?

Answer 24

• Food
• Water
• Aerosols
• Blood
• Bodily fluid

Question 25

What does the natural surface defence mechanism provide?

Answer 25

A formidable barrier

Question 26

What can a break in the natural surface defence mechanism cause?

Answer 26

Pathogenic infection

Question 27

What are the main points of entry for bacteria?

Answer 27

* Ingestion * Inhalation * Sexual transmission * Vertical transmission * Vectors * Trauma

Question 28

How can many pathogens cause disease?

Answer 28

Through toxin-mediated release

Question 29

What do some pathogens require to cause disease?

Answer 29

Colonisation of the host

Question 30

What does colonisation of the host require?

Answer 30

* Resistance to the flushing mechanism * Compete with the normal microbiota for colonisation of the mucosa

Question 31

Give an example of a flushing mechanism of the body?

Answer 31

The muco-ciliary escalator

Question 32

What features might a pathogen have to help them successfully colonise a host?

Answer 32

* Pili * Fimbriae * Flagella

Question 33

What is the purpose of pili and fimbriae?

Answer 33

Bind to host cell

Question 34

What are flagella used for?

Answer 34

Aid bacterial mobility

Question 35

What are flagella vital for?

Answer 35

The early phase of infection, especially in the GI tract

Question 36

By what mechanisms can bacterial cells gain access to the host cell?

Answer 36

* Simple endocytosis * Using molecular syringe to secrete effector proteins into the cell to allow for its uptake * Degrading enzymes for connective tissue or neighbouring cells can be released, and the bacterial cells can stay in the tissue and multiply

Question 37

What happens once bacterial cells have gained access to the host cell?

Answer 37

Toxins can be released, or there is potential for spread of the organisms into the bloodstream to cause pathogenic effects systemically

Question 38

How can bacteria cause pathogenic effects systemically?

Answer 38

Bacteria can stay in the tissue and release toxins into the bloodstream

Question 39

How can bacteria cause damage?

Answer 39

* Wide range of degrading enzymes * Secrete cytolysins

Question 40

What degrading enzymes can be secreted by bacteria?

Answer 40

* Proteases * DNAases * Collagenases * Lipases

Question 41

What is the effect of degrading enzymes secreted by bateria?

Answer 41

They cause tissue damage

Question 42

What do cytolysins do?

Answer 42

Damage the cytoplasmic membrane of the host cells, and cause cell death

Question 43

What are toxins?

Answer 43

Bacterial products that harm tissues or affect key biological events at local or distant sites, working in small concentrations

Question 44

What are the main types of toxins?

Answer 44

* Endotoxins * Exotoxins * Superantigens

Question 45

What are endotoxins also known as?

Answer 45

Lipopolysaccharides

Question 46

Where are endotoxins found?

Answer 46

In the outer membrane of Gram negative bacteria

Question 47

When can endotoxins be present in high levels?

Answer 47

During infection

Question 48

What do endotoxins do?

Answer 48

Promote inflammatory responses in individuals

Question 49

What is the result of the endotoxin promoted inflammatory response?

Answer 49

* Fever * Vasodilation

Question 50

What can endotoxins promote in very high concentrations?

Answer 50

Systemic inflammatory response syndrome (SIRS)

Question 51

What can endotoxins produce if left untreated?

Answer 51

* Septic shock * Fever * DIC * Multi-organ failure

Question 52

What are exotoxins?

Answer 52

Proteins produced by bacteria that disrupt the function or kill target cells

Question 53

How can exotoxins spread?

Answer 53

Systemically, *even if the bacteria producing them is only locally located*

Question 54

How do superantigens exert their effects?

Answer 54

By binding to T cell receptors and MHC class II, and mimicking the effects of antigen presentation

Question 55

What do the effects of superantigens produce?

Answer 55

An inflammatory response with SIRS like pathology

Question 56

What is a good example of a toxin mediated reponse?

Answer 56

The cholera toxin

Question 57

What is the cholera toxin composed of?

Answer 57

An A and 5 B subunits

Question 58

What do the B subunits of the cholera toxin do?

Answer 58

Activates GM1-ganglioside receptor on the intestinal cell

Question 59

What does the activation of the GM1-ganglioside receptor on the intestinal cell wall allow?

Answer 59

Endocytosis of the toxin

Question 60

What happens when the cholera toxin has been endocytosed?

Answer 60

It is cleaved

Question 61

What does the A subunit of the cholera toxin do?

Answer 61

Activate adenylyl cylase

Question 62

What is the result of the cholera toxin activating adenylyl cylase?

Answer 62

It causes an increase in cAMP, which stimulates the efflux of ions and thus the efflux of water

Question 63

What is the result of the efflux of water caused by the cholera toxin?

Answer 63

* Severe dehydration * Electrolyte imbalance

Question 64

What can the inflammatory response to a virus do?

Answer 64

Produce collateral tissue damage

Question 65

What is the collateral tissue damage caused by the inflammatory response to viruses mediated by?

Answer 65

* Neutrophils * Macrophages * Complement

Question 66

What can result from swelling caused by viruses?

Answer 66

Compromised tissue perfusion

Question 67

Why can viruses lead to an autoimmune response?

Answer 67

Due to mimicy of pathogen and tissue

Question 68

Give an example of where a virus leads to an autoimmune response

Answer 68

Rheumatic fever with S. Pyogenes

Question 69

How do viruses cause pathology?

Answer 69

* Direct viral cytopathogenesis * Viral immunopathogenesis

Question 70

What do viruses cause in direct viral cytopathogenesis?

Answer 70

* DNA damage * Alteration of the membrane structure * Direct cellular cytotoxicity of cellular components

Question 71

What develops from viral immunopathogenesis?

Answer 71

* Flu-like symptoms * Delayed hypersensitivity responses * Immune complex diseases develop

Question 72

What is the outcome of an infection dependent on?

Answer 72

* The virulence of the infecting pathogen * Age * Nutritional status * General health * Vaccination history * Genetic background * Site of infection * Number of invading pathogens

Question 73

By what mechanisms can the pathogen evade the host immune response?

Answer 73

* Polysaccharide capsules to prevent phagocytosis * Sheltering in protected zones * Producing enzymes to block chemotaxis * Blocking of opsonisation * Mimicry of antigens

Question 74

Give an example of a protected zone that a pathogen can shelter in?

Answer 74

Abscesses

Question 75

How can many pathogens persist?

Answer 75

As intacellular pathogens

Question 76

What must intracellular pathogens evade?

Answer 76

* Phagolysosomal fusion * Lysosomal enzymes * Many other mechanisms

Question 77

What must a pathogen do in order to spread and survive?

Answer 77

Move on to the next host directly, enter the environment, or via a vector

Question 78

What can a pathogens new environment serve as?

Answer 78

A reservoir for future amplification