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Miscellaneous > MCB Lecture 49 Pathogenesis I > Flashcards

MCB Lecture 49 Pathogenesis I Flashcards

0
Q

How may virulence be quantified?

A

By quantifying the amount of pathogen required to elicit death in the host.

LD50: the dose at which half of the population will die

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1
Q

What do Koch’s postulates describe?

List them

A

Koch’s postulates describe the requirements to confirm that a bacterium (or microorganism) is responsible for a disease.

  1. The bacterium must be found in every individual with the disease
  2. The bacteria must be localised to the lesion
  3. The bacteria must be able to be cultured outside the host for several generations
  4. Other organisms must be able to be infected by this culture
  5. The bacteria must elicit a specific immune response
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2
Q

What is LD50

A

The dose at which half of the population will die

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3
Q

What is the first stage of infection?

A

Adhesion to the host epithelial tissue

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4
Q

Compare the distribution of commensals with bacteria that are going to invade a host

A

Commensals are more loosely associated with host tissue, whereas invading bacteria are closely adhered to the tissue

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5
Q

How do bacteria adhere to the host cells?

A

Gram negative Bacteria with pilli have specific proteins on the end of their pilli.
These attach to specific oligosaccharides on the outside of the host’s cells.

  1. Fimbriae
  2. Non-fimbriae adhesins
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6
Q

Describe how it is possible for certain bacteria to infect specific tissues

A

The proteins on the outside of cells are tissue specific, that is different tissues have different oligosaccharides.

Thus, certain bacteria will have the correct pilli proteins to bind to the different tissues

Eg. Streptococcus have the correct pilli proteins to adhere to the tissue in the back of the throat

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7
Q

What is the evidence for fimbriae associated adhesion?

A
  1. When fimbriae were removed from the bacteria, the infection did not occur
  2. Hosts can generate antibodies to fimbriae, preventing infection
    Immunity may be active or passive
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8
Q

Describe the case of ETEC in piglets

A

ETEC is a bacterium that causes an infection that causes diarrhoea in piglets.
The bacterium colonise in the gut

The mother pigs are vaccinated by giving them the bacterial fimbriae. The mothers develop antibodies to the fimbriae

The baby piglets receive the antibodies in the milk.
The antibodies kill the bacteria when they get into the gut

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9
Q

Once adhered to the host, what must bacteria do?

A

Penetrate

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10
Q

How do bacteria get into the epithelial cells

Give an example

A

Invasins

Eg. Yersinia
Invasins are molecules on the surface of the bacterium that bind to epithelial cells, and bring about endocytosis of the bacterium.

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11
Q

What is are the two mechanisms used by bacteria to survive once inside the body?

A
  1. Pyogenic bacteria: Preventing the macrophages or other phagocytes from eating them
  2. Intracellular parasites: avoid killing once in the phagocyte
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12
Q

Which molecules are released by bacteria to prevent phagocytosis?

A

Leukocidins

Anti-inflammatory molecules: inflammatory and immune cells are not brought to the site of infection

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13
Q

Explain how capsules prevent phagocytosis

A

Capsules provide:

  • Electrostatic repulsion
  • Hide the underlying features
  • Resemble host

They can prevent binding of antibodies and thus opsonisation in some cases

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14
Q

What are the three pathways for opsonisation of a bacterium?

A
  1. Non-specific: macrophage takes up bacterium at random
  2. Classical pathway: antibody (IgM) and complement (C3b) binds to the capsule
  3. Antibody (IgG) and C3b binds to bacterium. Phagocyte expresses FcRecpetor and C3bR
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15
Q

To what do invasions bind, allowing the entry of the bacterium?

A

Integrins on the host cell

16
Q

What do pyogenic bacteria do?

A

They avoid phagocytosis

17
Q

What is the classification of the diphtheria bacterium?

A

Gram positive rod

18
Q

Does bacterial DNA or RNA activate a PRR?

A

DNA

It is viral RNA that acts as a PAMP

19
Q

What are the features of Bacillus anthracis?

A

Gram + rod
Slime layer
Spore forming

20
Q

What are the features of clostridium tetani?

A 
G+ rod
Anaerobic
Exotoxin: tetanospasmin
Spore forming
Vaccine: uses toxin lids
Found in soil or gastrointestinal tract
21
Q

What are the features of E. coli?

A 
G- rod
Serotyped with O and H antigen
Highly variable genome
ETEC: Enterotoxin disrupts permeability of gut -> diarrhoea
Fimbriae attachment
22
Q

What are the features of C. Diphtheriae?

A

G+ rod
Exotoxin: diphtheria toxin that disrupts host protein synthesis
Vaccine uses toxinoids

23
Q

Describe the type of vaccine for bacteria that produce exotoxins

A

Vaccine uses toxinoids

24
Q

What are the features of staphylococcus aureus?

A 
G+ coccus
Common commensal
Respiratory infection
Food poisoning
Exotoxin causes TSS (it's a superantigen)
25
Q

What are the features of staphylococcus pyrogens?

A

G+ coccus

Exotoxin is a superantigen producing TSS

26
Q

What are the features of Klebisiella?

A

Capsulated

27
Q

How does the host overcome capsules to prevent infection?

A

Once encapsulated bacteria are within the body, it is too late. They can’t be phagocytosed unless we have antibodies

Immunity can only be gotten by

  • passive immunity: transfusion of capsule antibodies
  • active: vaccinate the individual with capsule protein to stimulate the production of capsule antibodies
28
Q

Which vaccine uses bacterial capsule proteins to give immunity?

A

Streptococcus pneumoniae

29
Q

What are the features of Yersinia pestis?

A

G- rod

Invasin on outer cell membrane that causes pathogen-mediated endocytosis

30
Q

What are the features of mycobacterium tuberculosis?

A

Acid fast
Intracellular pathogen: survives inside alveolar macrophages
Bacillus
Hardy
Highly aerobic
PAMP is lipoarabinomannam, unique to its cell wall

31
Q

What are the features of vibrio cholerae?

A

G- rod
Exotoxin is cholera toxin
Fimbriae adhesion in the gut

32
Q

What are the features of streptococcus pneumoniae?

A

G+ coccus
Encapsulated
Vaccine contains capsule protein

33
Q

What are the features of salmonella

A

G- rod
Intracellular pathogen: escapes from the phagosome
Enterobacteria: enters by contaminated food

34
Q

How do extracellular pathogen evade phagocytosis?

A
  • secrete Leukocidins
  • secrete anti-inflammatory toxins and enzymes
  • capsules
  • secrete pus (pyogenic bacteria)
35
Q

Give some examples of toxin mediated disease

A 
Staphylococcal food poisoning
Staphylococcal toxic shock syndrome
Botulism
Tetanus
Diphtheria
36
Q

What causes botulism?

A

Botulinum toxin

It is an exotoxin produced by Clostridium botulinum

37
Q

What is the manifestation of botulinum?

A

Paralysis

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