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BOD > Respiratory Tract Pathogens > Flashcards

Respiratory Tract Pathogens Flashcards

1
Q

What causes diphtheria?

A

Gram-positive rod

Corynebacterium diphtheriae

Extracellular toxigenic bacterium

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2
Q

Where does the gene for diphtheria toxin come from?

A

Carried on bacteriophage and inserted into bacterial chromosome

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3
Q

What controls the diphtheria toxin gene?

A

Bacterial transcription factor DtxR

Represses gene expression when bound to iron

Transcription turned on in host where iron concentration is low

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4
Q

What part of the respiratory tract does diphtheria colonise?

A

The nasopharynx

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5
Q

What does the diphtheria toxin cause?

A
  1. Intense local inflammation
  2. Damage to mucosal cells
  3. Growth of bacteria in inflammatory exudate
  4. Formation of pseudomembrane - occludes airway
  5. Irregular heartbeat, coma, death
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6
Q

How does diphtheria toxin enter cells?

A

Receptor mediated endocytosis

B binds to heparin-binding epidermal growth factor

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7
Q

What is furin?

A

A host protease that nicks the A-B polypeptide, but the components remain attached by a disulphide bridge

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8
Q

How does diphtheria toxin A translocate into the cytosol?

A

Acidification of endosome by V-ATPase triggers B-dependent translocation of A across vesicle membrane into cytosol

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9
Q

What does Streptococcus pyogenes cause?

A

Pharyngitis

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10
Q

Where does S. pyogenes colonise?

A

Throat epithelium

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11
Q

What proteins does S. pyogenes produce?

A
  1. Surface M protein
  2. C5a peptidase
  3. Streptolysins O and S
  4. Pyogenic toxins
  5. Hyaluronidase
  6. Streptokinase
  7. DNAse
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12
Q

What causes strangles?

A

Streptococcus equi

Characterised by purulent nasal discharge and abscesses in lymph nodes in neck

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13
Q

What is bastard strangles?

A

Systemic strangles

Recovered horses are carrier state

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14
Q

Where does pneumonia colonise?

A

Nasopharynx

Migrates to lower respiratory tract

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15
Q

How does pneumonia resist removal by mucous and ciliated cells?

A
  1. Pneumolysin

2. Secretory IgA protease

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16
Q

How does pneumonia avoid phagocytosis by alveolar macrophages?

A
  1. Pneumolysin

2. Polysaccharide capsule

17
Q

Where does pertussis colonise?

A

Respiratory epithelium

18
Q

How does pertussis damage epithelial cells?

A
  1. Lipid A
  2. Pertussis toxin
  3. Adenylate cyclase that mimics host AC
19
Q

What causes pneumonic plague?

A

Yersinia pestis

20
Q

What symptoms does the plague cause?

A
  1. Haemorrhagic inflammation
  2. Spread to blood and lung
  3. Multi-organ failure
  4. Necrotic lesions
21
Q

What virulence factors does Y. pestis have?

A
  1. Antiphagocytic capsule
  2. Protein toxins - YopP and YopT
  3. LPS lipid A
22
Q

What makes the coat of M. tuberculosis impermeable?

A

Waxy acid-fast coat

Contains mycolic acid

Resistant to drying and disinfectants

23
Q

How does M. tuberculosis spread?

A

Spread by small droplets

Ingested by alveolar macrophages

Inhibits phagosome-lysosome fusion to prevent intracellular killing

Multiplies in macrophages

Crosses alveolar epithelium when macrophages lyse

Enters lymphatics and spread around body

24
Q

What protein facilitates dissemination of TB in body?

A

ESAT6

Pore-forming toxin

Interferes with macrophage signalling pathways

Down-regulates production of ROS

25
Q

What is the immune response to TB?

A

TH1 cells activate macrophages via IFNγ

TNFα secretion and production of NO

26
Q

What is the basis of the tuberculin skin test?

A

CD4+ T cell activity

27
Q

What does persisting TB infection cause?

A

Type IV granulomatous inflammation

Aggregates of activated macrophages, fibroblasts and lymphocytes wall off pathogen

Granulomas show ongoing necrosis, repair and inflammation

Concentrated release of lytic enzymes results in caseous necrosis (cheese-like) - aids spread (miliary TB)

BOD (8 decks)

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