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Infection > Streptococcus > Flashcards

Streptococcus Flashcards

1
Q

streptococi characteristics

A

(especially pyogenes)

  • Gram positive
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2
Q

how do you classify streptocci

A

haemolysis

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3
Q

explain haemolysis

A

Use agar with blood (horse or sheep)- with RBC.

  • Iron is a requirement for many bacteria, therefore haemolysis to get iron
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4
Q

partial haemolysis

A

alpha haemolysis

e.g. viridans (green) streptococcus

(live in the mouth)

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5
Q

complete haemolysis

A

beta haemolysis

  • streptocccus pyogenes
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6
Q

no haemolysis

A

gamma non-hamolysis

e.g. enterococcus faecalis

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7
Q

streptococcus classification schemes

A
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8
Q

streptococcus pyogenes virulence factors

A
  • hyaluornic acid capsule
  • M protein
  • Adhesins
  • Streptolysins O and S
  • DNAases A, B, C and D
  • Hyaluronidase
  • streptokinase
  • streptooccal pyrogenic exotoxins
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9
Q

Hyaluronic acid capsule

A
  • Inhibits phagocytosis by neutrophils and macrophages
  • Poor immunogen because of similarity to human connective tissue hyaluronate
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10
Q

M protein

A
    • Resistance to phagocytosis by inhibiting activation of alternative complement pathway on bacterial cell surface
      • >150 antigenically different serotypes as a consequence of nucleotide variants of the M gene
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11
Q

Adhesins (Lipoteichoic acid, M protein, fibronectin binding proteins)

A

Adherence is first step in colonisation/ infection

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12
Q

Streptolysins O and S

A

Lysis of erythrocytes, neutrophils, platelets

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13
Q

DNAases A, B, C and D

A

Degradation of DNA

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14
Q
A
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15
Q

Hyaluronidase

A

Degradation of hyaluronic acid in connective tissue

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16
Q

Streptokinase

A

Dissolution of clots through conversion of plasminogen to plasmin

17
Q

Streptococcal pyrogenic exotoxins

A

Cleaves Ig G bound to group A steep

18
Q

Streptococcus pyogenes M protein

A

If you stain bacteria correctly you can see fuzzy layerà M proteins

19
Q

Streptococcal pharyngitis (tonsillitis)

A
  • Causative organism: streptococcus pyogenes
  • Most common at 5-15 years
  • Droplet spread
  • Association with overcrowding
  • Untreated patients develop M protein specific antibodies
20
Q

clinical features of streptococcal pharyngitis

A
  • Abrupt onset of sore threat
  • Malaise, fever, headache
  • Lymphoid hyperplasia
  • Tonsillopharyngeal exudates
  • Throat swab –> Group A strep
21
Q

Complications of streptococcal pharyngitis

A

scarlet fever

suppurative complications

acute rheumatic fever

acute post-streptococcal glomerulonephritis

22
Q

Scarlet fever

A
  • Due to infection with streptococcal pyrogenic exotoxin strain of S. Pyogenes
  • Local or haematogenous spread
  • High fever, sepsis, arthritis, jaundice
  • 1800s epidemic with 20% mortality
23
Q

Suppurative complications

A
  • Peritonsillar cellulitis/abscess (contiguous)
  • Retropharyngeal abscess
  • Mastoiditis, sinusitis, otitis media
  • Meningitis, brain abscess (haematogenous spread)
24
Q
A
25
Q

Acute rheumatic fever

A
  • Inflammation of the heart, joints, CNS
  • Follow on from pharyngitis
    • No bacteria anymore (no point using antibiotics)
  • Rheumatogenic M types
  • Mechanisms (possible)
    • Auto-immune
    • Serum sickness
    • Binding of M protein to collagen
    • ASO, ASS induced tissue injury
26
Q

Acute post-streptococcal glomerulonephritis

A
  • Acute inflammation of renal glomerulus
  • M type specific but not same as ARF M types
  • Antigen-antibody complexes in glomerulus
27
Q

Streptococcus pyogenes skin infections

A

impetigo

erysipelas

cellulitis

necrotising fasciitis

28
Q

impetigo

A
  • Childhood infection (2-5 years)
  • Initial skin colonisation followed by intradermal inoculation
  • No ARF but impetigo is most common cause of glomerulonephritis
  • Flucloxacillin
29
Q
A
30
Q

Erysipelas

A
  • Dermis infection with lymphatic involvement
  • Face, lower limbs
  • Facial lesions frequently preceded by pharyngitis
  • Lower limb infection usually secondary to invasion of skin via trauma, skin disease or local fungal infection
31
Q

Cellulitis

A
  • Skin and subcutaneous tissue infection
  • Impaired lymphatic drainage and illicit injecting drug use important risk factor
32
Q

Necrotising fasciitis (may require surgery)

A
  • Infection of deeper subcutaneous tissue and fascia
  • Rapid, extensive necrosis
  • Usually secondary to skin break
  • Severe pain, even before gross clinical changes
  • High fever, fulminant course, high mortality (20-70%)
33
Q

normal skin vs necrotising fascitis

A
34
Q

Streptococcal toxic shock syndrome

*

A
  • Deep tissue infection with strep pyogenes
  • And
  • Bacteraemia
  • And
  • Vascular collapse
  • And
  • Organ failure
35
Q

Deep tissue infection with strep pyogenes- from health to death in hours

A
  1. Entry of group A strep into deeper tissue sand bloodstream
  2. Streptococcal pyrogenic exotoxins stimulate T cells through binding to MHC class II APC and V-B region of T cell receptor inducing:
    1. Monocyte cytokines (TNF-alpha, IL-1B, IL-6) and lymphokines (TNF-B, IL-2, IFN-Y)
    2. M-protein fibrinogen complex formation

Infection (36 decks)

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