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
2
Q
Staph Aureus - Niche
A
- Colonizes opening of nose
- Facultative anaerobe
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
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
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
6
Q
Exfoliatin
A
Exfoliatin
- Staph Aureus exotoxin
- Disrupts intercellular junctions in skin
- Causes Scalded Skin Syndrome
7
Q
Alpha toxin (alpha hemolysin)
A
Alpha toxin (alpha hemolysin)
- Staph aureus exotoxin
- Pore forming toxin => lyses host cells
- Responsible for B hemolysis
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
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
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
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)
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
- Janeway lesions
- 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
13
Q
Staph aureus - Abcesses
A
ASPEONS
Faciliated by coagulase
14
Q
Septic Arthritis
A
ASPEONS
Staph aureus is # cause in adults
15
Q
Staph aureus - Pneumonia
A
Patchy infiltrates on X-Ray
Secondary to viral infection
Staph aureus #1 cause of nosocomial pneumonia
