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Gram Positive Cocci Flashcards

1
Q

Staph Aureus - Diagnostic Profile

A
  • Gram positive, coccus
  • Facultative anaerobe
  • Grape like clusters
  • Golden colonies on blood agar
  • Beta hemolytic
  • Catalase positive
  • Coagulase positive
  • Most virulent staphylococcus
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2
Q

Staph Aureus - Niche

A
  • Colonizes opening of nose
  • Facultative anaerobe
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3
Q

Staph Aureus - Determinants of Pathogenicity

A
  • TSST-1
    • Superantigen
    • Causes shock (even in absence of bacteria)
  • Staphylococcal Enterotoxins (A-E, G-I)
    • Bind Upper GI neurons => vomit in 2-5 hours, self limited food poisoning
    • Super antigen => Shock
    • Resistant to 30 min boiling and digestive enzymes
  • Exfoliatin
    • Disrupts intercellular junctions in skin
    • Causes Scalded Skin Syndrome
  • Alpha toxin (alpha hemolysin)
    • Pore forming toxin => lyses host cells
    • Responsible for B hemolysis
  • Panton-Valentine Leukocidin (PVL)
    • Pore forming toxin => host cell lysis
    • Assoicated with community acquired MRSA
    • Causes severe necrotic skin infections
    • PVL gene encoded by phage
  • Coagulase
    • Binds prothrombin & initiates fibrin polymerization
    • Causes clot formation
  • Protein A
    • Binds Fc portion of IgG and blocks complement binding
    • Prevents opsonization and phagocytosis
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4
Q

TSST-1

A

Toxic shock syndrome toxin 1

  • Staph aureus exotoxin
  • Superantigen
  • Causes shock
    • Even in absence of bacteremia e.g. wound packing or tampon
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5
Q

Staphylococcal Enterotoxins

A

Staphylococcal enterotoxins (A-E, G-I)

  • Bind Upper GI neurons => vomit in 2-5 hours, self limited food poisoning
  • Super antigen => Shock
  • Resistant to 30 min boiling and digestive enzymes
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6
Q

Exfoliatin

A

Exfoliatin

  • Staph Aureus exotoxin
  • Disrupts intercellular junctions in skin
  • Causes Scalded Skin Syndrome
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7
Q

Alpha toxin (alpha hemolysin)

A

Alpha toxin (alpha hemolysin)

  • Staph aureus exotoxin
  • Pore forming toxin => lyses host cells
  • Responsible for B hemolysis
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8
Q

Panton-Valentine Leukocidin (PVL)

A

Panton-Valentine Leukocidin (PVL)

  • Staph aureus exotoxin
  • Pore forming toxin => host cell lysis
  • Causes severe necrotic skin infections
  • Assoicated with community acquired MRSA
  • PVL gene encoded by phage
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9
Q

Coagulase

A

Coagulase

  • Staph aureus toxin
  • Binds prothrombin & initiates fibrin polymerization
  • Causes clot formation
  • Contributes to fibrin capsule surrounding many abscesses
    • Mechanical barrier to neutrophil entry
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10
Q

Protein A

A

Protein A

  • Staph aureus cell wall component
  • Binds Fc portion of IgG and blocks complement binding
  • Prevents opsonization and phagocytosis
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11
Q

Superantigen

A

Superantigen

  • Activates entire subsets of T cells => Cytokine overload
    • Binds MHCII
    • Links MHC II to whole classes of T-cell receptors with specific Vß domains
  • Cytokines cause fever, shock, and organ failure
    • E.g. IL-1B and TNF-A
  • Many bacterial toxins are superantigens
    • Staph aureus TSST-1
    • Staph aureus Enterotoxins (A-E,G-I)
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12
Q

Staph Aureus - Microbe Mediated Diseases

A
  • ASP EONS
  • Abcesses
    • Faciliated by coagulase
  • Septic Arthritis
    • # 1 cause in adults
  • Pneumonia
    • Patchy infiltrates on X-Ray
    • Secondary to viral infection
    • Staph aureus #1 cause of nosocomial pneumonia
  • Acute Endocarditis
    • Rapid onset
    • Common in IV drug users
    • Biofilm on valve (esp tricuspid)
    • Hard to eradicate => frequent death
    • Clinical signs (J’COH)
      • Janeway lesions
        • Lesions on soles and palms
      • Conjunctival hemorrhages
        • Tiny blood clots in eye white
      • Osler’s nodes
        • Painful swellings
      • Heart murmurs
  • Osteomyelitis
    • # 1 cause in adults
  • Nosocomial Infections
    • Frequent cause of nosocomial infections
    • # 1 cause of nosocomial pneumonia
    • Frequent cause of surgical wound infections
  • Skin & Soft Tissue Infections
    • S. aureus and Group A Strep leading cause
    • Folliculitis (Furuncle, Carbuncle)
    • Cellulitis
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13
Q

Staph aureus - Abcesses

A

ASPEONS

Faciliated by coagulase

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14
Q

Septic Arthritis

A

ASPEONS

Staph aureus is # cause in adults

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15
Q

Staph aureus - Pneumonia

A

Patchy infiltrates on X-Ray
Secondary to viral infection

Staph aureus #1 cause of nosocomial pneumonia

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16
Q

Acute Endocarditis

A

ASPEONS

  • Rapid onset
  • Common in IV drug users
  • Biofilm on valve (esp tricuspid)
  • Hard to eradicate => frequent death
  • Clinical signs (J’COH)
    • Janeway lesions
      • Lesions on soles and palms
    • Conjunctival hemorrhages
      • Tiny blood clots in eye white
    • Osler’s nodes
      • Painful swellings
    • Heart murmurs
17
Q

Osteomyelitis

A

Staph aureus is #1 cause in adults

18
Q

Staph aureus - Nosocomial Infections

A

ASPEONS

  • Staph areus frequent cause of nosocomial infections
  • # 1 cause of nosocomial pneumonia
  • Frequent cause of surgical wound infections
19
Q

Staph Aureus - Skin + Soft Tissue Infections

A

S. aureus and Group A Strep leading cause

Folliculitis (Furuncle, Carbuncle)
Cellulitis

FDN3 - Bacteria (1 decks)

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