Lecture 2 - Bacterial Pathogenesis Flashcards Preview

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Flashcards in Lecture 2 - Bacterial Pathogenesis Deck (63):
1

Differentiate between pathogens, opportunistic pathogens and normal flora

Pathogens: inherently cause disease

Opportunistic pathogens: only cause disease when given the chance (when host is immunosupressed, antacids etc.)

Normal flora: bacteria that are present in the gut under normal circumstances and do not cause adverse effects

2

Describe how a bacterium can be normal flora, opportunistic infection as well as a pathogen

Staphylococcus aureus
It is normally found on the skin - doesn't cause disease.
However, when an individual is immunosupressed, it may cause disease

Toxin production in food can cause intoxication

3

What is a 'virulent organism'?

This is an organism that is likely to cause disease

4

What is an 'avirulent organism'?

This is an organism that won't cause disease under normal circumstances (eg. normal physiology)

5

What are virulence determinants?
Give some examples

Characteristics that make an organism virulent
eg.
Pilli
Toxins
Capsules
Exzymes
Siderophores

6

What are some 'opportunities' for commensals to cause disease?

Immuno compromised individual
Antacids taken
Pathogen is moved (site specific)

7

Why are commensals important?

They contribute to:
- immune system
- metabolism

8

When does an infection go from asymptomatic to symptomatic?

After replication, when there is damage to host dissue

9

What is the generalised process of bacterial replication?

Colonisation
Penetration
Replication
Damage to host
Disease
Dissemination
Immunity

10

Describe how colonisation occurs

What are the two types of colonisation

Attachment:
• surface molecule (binding molecule / adhesin) + host receptor

Fimbrial / non - fimbrial

11

Why are epithelial cells said to be polarised?

Different ends of the cell have different expression of receptors

12

Why is polarisation of epithelial cells important?

Bacteria may need to damage epithelium to gain access to receptors

13

What are the two functions of fimbriae?

• Adhesion
• Conjugation

14

What is the structure of fimbriae?

Hollow protein tube
Adhesin on the tip

15

Which part of a pilus binds to the host cells receptor?

The adhesin on the tip

16

How do we know fimbriae are involved in colonisation?

• Can be used as antigen in vaccines for immunity

• Infection blocked by antibodies to fimbriae

17

How does a Urinary tract infection arise?

Bacteria from the rectum 'ascend' to cause an infection in the bladder

18

Who is more commonly affected by UTIs?
Why?

Women
Shorter urethra

19

Which bacterium is responsible for UTIs?

Uropathogenic E. coli

20

How do uropathogenic E. coli cause disease?

1. 'P' fimbrial attachment to bladder epithelium
2. Bacteria internalised
3. Replicate to high levels

21

What is non-fimbrial adhesion?

This is when bacteria adhere to the host cell with molecules present on their cell wall
• glycocalyces (slime layer, capsule)
• teichoic acids

22

Give an example of non-fimbrial adhesion

Staphylococcus aureus adheres using Teichoic acids of the cell wall to the fibronectin and collagen of the host

Teichoic acid -- Fibronectin

23

What are the two forms of glycocalyx?
How may they be differentiated?

Slime layer
Capsule

Slime layer can be washed away?

24

What is the function of glycocalyx?

- Evasion of host defences by masking antigens
- Adhesion

25

What is a biofilm?

Any group of microorganisms in which cells stick to each other on a surface

26

Is penetration required for disease?

No,
some pathogens are extracellular

27

Describe how bacteria penetrate cells

RME: receptor mediated endocytosis
• Invasins

Invasin or molecule on bacteria binds to a receptor on the host cell --> taken up into the cell

28

How do bacteria spread between cells?

When bacteria penetrate a cell, they can alter the features of the cell, such an cellular junctions

Tight junctions become more leaky --> bacteria can spread more easily

29

How does Pseudomonas cause disease, considering that it lacks the ability to invade

It can only invade when there is damage to the epithelium - such as in burns victims

30

Where are the different locations where bacterial replication can occur?

1. On cells (extracellularly)

2. Intracellularly
• endosome
• cytoplasm

31

What are the pros and cons of the different locations of intracellular bacterial replication?

Endosome:
pro: more protection from molecules in the cytosol
con: less nutrients

and vice versa

32

True of false: penetration and replication are essential for infectious disease?

False
Only replication is essential

Bacteria can cause disease extracellularly

33

Describe the features of the bacterial growth curve

Lag phase:
Log phase: exponential growth of bacteria, diving by binary fission
Plateau: stable numbers
Decline: due to competition for resources and quroum sensing

34

True or false?
There can be many different species of bacteria in a biofilm

True
Normally not just one species

35

What do biofilms contain?

Bacteria
Glycocalyces
Metabolites

These hold the bacteria together

36

What controls the formation of a biofilm?

Quorum sensing

37

What is quorum sensing?

Recognition of bacteria within a colony by chemical signals released by neighbouring bacteria

38

What happens when there are sufficient numbers of bacteria?

A quorum

The signal takes effect

39

What are the two types of signal in quorum sensing?

Generic
Specific

40

What are biofilms normally associated with?

Chronic infection

41

What sort of genes do signals from quroum sensing regulate?

Replication
Biofilm production
Virulence determinants

42

What happens to metabolic activity in a biofilm?

Reduced metabolic activity, because the bacteria can rely on their neighbours and become more efficient

43

Why are microfilms bad?

- Increased expression of virulence determinants
- Protection form host defences
- Greater opportunity for gene transfer

44

When does an infection pass from subclinical to disease?

Subclinical: numbers below the threshold
Disease: numbers above a certain threshold

45

How may physical barriers be subverted by bacteria?

Trauma
Surgury

46

How may the complement system by avoided by bacteria?

Enzymes that destroy C'

47

How do bacteria evade phagocytes?

- Capsules
- Escape phagosome
- Survive in phagosome
- Kill phagocytes

48

How do bacteria evade Ab?

Enzymatic destruction

49

How do bacteria evade APCs?

Down regulate MHC expression to reduce the efficiency of APCs

50

What are the three ways that bacteria can cause damage to the host?

Endotoxin
Exotoxin
Immunopathology

51

In general, how does exotoxin work?

1. Produced by bacteria
2. Gets into host cell (B subunit)
3. Cytotonic, cytotoxinc (A subunit)

52

When is endotoxin primarily produced?

When cells die

53

What is the structure of endotoxin?

Polysaccharide
Lipid A

54

What is the effect of LPS?

• Activates the alternate complement pathway
• Binds and activates macrophages and neutrophils by PRRs

55

Describe how bacteria disseminate

Give some examples

1. They produce compounds that break down:
• intercellular matrices
• cells

For example:
• Hyaluronidase
• collagenases
• elastases

2. Use host physiology
• blood
• nervous system

56

Describe how bacteria can use the host's physiology to disseminate

Neuronal transport

Blood circulation
• intra / extracellular

57

Why is infection a race? Who are the competitors?

It is a race:
Pathogen vs. Host's immune system

Immune system wins: recovery
Pathogen wins: loss of function, death
Pathogen partially wins: chronic infection, latency

58

How can we affect the outcome of 'The Race'?

• Maintain physical barriers
• Maintain innate IR
• Maintain adaptive IR
• Reduce virulence of organism
• Reduce n° of organisms

59

What are some features of normal flora?

• mutualistic relationship with host (don't cause disease)
• cause disease if moved to another area
• occupy the niche to prevent pathogens colonising
• contribute to immune system and metabolism
• Can be transient / stable

60

TRUE / FALSE:
In Biofilms there is increased:
• metabolic activity
• expression of virulence determinants
• replication
• gene transfer
• protection from host and antibiotics

• metabolic activity FALSE
• expression of virulence determinants TRUE
• replication TRUE
• gene transfer TRUE
• protection TRUE

61

How do bacteria kill phagocytes?

Leucocidins

62

Draw a typical AB5 exotoxin

Slide 26

63

When is endotoxin mainly produced?

When G- bacteria die