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302- SBM > Infection 3: Bacterial pathogenesis > Flashcards

Infection 3: Bacterial pathogenesis Flashcards

1
Q

Describe the bacterial envelope structure of gram positive bacteria

A

Thick peptidoglycans layer

Lipoteichoic and teichoic acid

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2
Q

Describe the bacterial envelope structure of gram negative bacteria

A

Outer membrane

  • Lipopolysaccharide
  • Proteins and pores

Thin peptidoglycans

Inner membrane

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3
Q

Name a bacterial organism that is an aerobe

A

S. aureus

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4
Q

Name a bacterial organism that is an anaerobe

A

Clostridium Spp

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5
Q

Is E.coli an anaerobe or aerobe?

A

both

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6
Q

How can we classify Streptocci?

A

α haemolytic ‘viridans’ streptococci

β haemolytic streptococci

γ (non)- haemolytic streptococci

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7
Q

α haemolytic ‘viridans’ streptococci

A

These cause partial haemolysis of blood agar and a greenish colour

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8
Q

β haemolytic streptococci

A

These cause complete haemolysis making the blood agar translucent

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9
Q

Gram positive cocci

A 
Staphylococci
S. aureus
Coagulase negative staphylococci
Streptococci
Group A streptococcus (S. pyogenes)
Group B
Group C and G
Group D = enterococcus
S. pneumoniae
Viridans type streptococci
Peptococcus / Peptostreptococcus
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10
Q

Gram negative cocci

A

Neisseria
N. meningitidis
N. gonorrhoea
Moraxella (Branhamella) catarrhalis

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11
Q

Gram positive rods (bacilli)

A 
Bacillus e.g.  B. cerus and B. anthracis
Corynebacterium
Propionibacterium
Listeria monocytogenes
Clostridium e.g. C. difficile
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12
Q

Gram negative rods

A 
Haemophilus influenzae
Enterobacteriaciae
Salmonella & Shigella
Eschericia coli
Klebsiella and Enterobacter
Proteus
Pseudomonas e.g P. aeruginosa
Bacteroides e.g. B. fragilis
Campylobacter and Helicobacter
Vibrio cholerae
Bordetella pertussis
Legionella
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13
Q

What is the significance of s aureus?

A

positive coagulase test would indicate the presence of S. aureus.

Coagulase normally stimulates clotting
Role in immune evasion
Not expressed by less virulent ‘coagulase negative’ staphs

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14
Q

In the context of s aureus, what are adhesins? Give an example

A

surface proteins which bind host proteins

S aureus can colonize host to initiate infection by adhering to components of the extracellular matrix.

Adherence is mediated by surface protein adhesins

E.g Protein A
- binds Fc portion of IgG

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15
Q

Name the toxins produced the strains of staph aureus

A

Cytotoxins

  • Pore forming toxins, lyse host cells
  • Panton-valentine leukocidin (PVL) – lyses polymorphs

Exfoliative toxins

  • Proteases
  • Target epidermal structural proteins

Enterotoxins (superantigens)
- Stimulate massive T cell activation ?immune evasion

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16
Q

Name 2 exotoxins produced by strains of Staphylococcus aureus

A

TSST-1 or Exfoliative toxin 1

17
Q

What syndrome of infection is TSST-1 associated with?

A

Toxic shock

Superangtigen exotoxins

Mechanism- stimulate massive T cell activation

a. Rash
b. Renal failure
c. Septic shock
d. Multiorgan failure
e. Skin desquamation on recovery

18
Q

What syndrome of infection is Exfoliative toxin 1 associated with?

A

Scalded skin syndrome

Mechanism:
Serine proteases - specific for desmoglein I (epidermal structural proteins)

19
Q

Name a cytotoxin produced by strains of staph aureus.

A

Panton-valentine leukocidin (PVL) –

Mechanism- lyses polymorphs
Pore forming toxins, lyse host cells

20
Q

Outline the mechanism by which s aureus causes food poisoning

A

Toxin mediated

specifically enterotoxins/ s aureus superantigens

21
Q

Give an example of a Coagulase Negative Staphylococci

A

S epidermis

Staining is same as s.aurerus
Don’t make coagulase
Less virulent

22
Q

Describe the virulence of S. epidermidis

A
  • lives on the skin
  • frequently contaminates blood culture
  • Also a pathogen
  • Central venous line infection
    Endocarditis (prosthetic valve)
    Orthopaedic surgical infections
    Foreign material in a ‘sterile’ place
    grafts, implants etc
23
Q

What is the accurate name of s pyogenes?

A

group A strep and is a beta haemolytic strep

24
Q

Outline the spectrum of disease caused by s pyogenes

A

Superficial infections

  • Pharyngitis
  • Cellulitis

Deep infections

  • Severe soft tissue infection
  • myositis
  • necrotising fasciitis

Autoimmune sequelae (v. rare in UK)

  • Rheumatic fever – a major cause of heart disease
  • glomerulonephritis
25
Q

Outline the virulence factor for s pyogenes

A

M protein

  • A major antigenic determinant of S. pyogenes
    Immunity is type specific.
  • A major virulence factor
    Binds serum factor H – regulator of complement activation
  • Prevents opsonisation
    Involved in pathogenicity
  • Has an alpha-helical ‘coiled-coil’ protein
  • Molecular mimickry
26
Q

Explain the term molecular mimicry in the context of post infective autoimmune disease and give an example and organism.

A
  • structural similarity of microbial antigenic determinants and host proteins resulting in cross reactivity of antibody and T cell responses to microbial antigens with self antigens

Example is Rheumatic fever

S pyogenes

27
Q

Describe the virulence mechanisms of E coli

A
  1. Adhesins eg pili
  2. Capsule
  3. Siderophores
28
Q

Major diseases caused by E coli

A

UTI
Enteric
Meningitis (Neonatal, elderly, immunocompromised)

29
Q

Virulence mechanism of E. coli

  • Adhesins
A
  1. Adhesins eg pili
    ( E. coli adhesins are fimbrial, fibrillar and nonfimbrial.)
    Colonization of host tissues mediated by adhesins
30
Q

Virulence mechanism of E. coli

  • Capsule
A
  1. Capsule- Protects from complement mediated responses
    Important early in life (lack of antibody)
    a/w particular disease manifestations e.g. K1 capsular serotype and neonatal meningitis
    Mechanism? Adhesin interactions with blood brain barrier
31
Q

Virulence mechanism of E. coli

  • Sideropores
A
  1. Siderophores- Enterobactin
    Powerful iron chelators
    Essential for survival in tissues (very low free Fe3+ environment)
32
Q

Virulence mechanism of E. coli

  • Toxins
A
  • Endotoxin (= …………………….)
  • Exotoxins
  • Cytolysins (like Gram positive streptolysins)
  • Enterotoxins very different from staphylococcal enterotoxins - cause fluid leak in the GI tract
  • Verotoxins
    Disrupt ribosomal protein synthesis
    Verotoxin producing strains cause haemorrhagic diarrhoea
    Enterohaemorrhagic E. coli (EHEC) e.g. O157:H7
    Associated with haemolytic uraemic syndrome (HUS)

302- SBM (27 decks)

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