4 Gram Positive Cocci (Infectious Bacterial Agents)

Question 1

Staphylococci

Answer 1

• Grape like clusters
• Normal flora
• Catalase positive
• S. Aureus secrete coagulase and appear yellow/gold on blood agar and produces Beta hemolysis

Question 2

S. aureus virulence factors

Answer 2

• Capsule/Protein A: resists phagocytosis
• Fibronectin binding protein (FnBP): adhesion
• Panton-Valentine leukocydin: neutrophil lysis (MRSA)
• Superantigen exotoxins: Toxic shock syndrome toxin (TSST-1); Exfoliating toxin (ET)

Question 3

Clinical Significance

Answer 3

• Localized skin infections
• Deep skin infections
• Septicemia
• Toxinosis: toxic shock syndrome
• Antibiotic resistance: MRSA, HA-MRSA, CA-MRSA

Question 4

This S. aureus toxin cause the lysis of PMNs (neutrophils)

Answer 4

Panton-Valentine leukocydin

Question 5

Coagulase negative Staphylococci

Answer 5

S. epidermidis - common cause of infections of catheters and heart valves

Question 6

Streptococci

Answer 6

• Gram positive (pairs/chains), nonmotile, catalase negative.
• S. pyogenes, S. agalactiae, S. pneumoniae, Enterococcus sp.

Question 7

Classification

Answer 7

• Hemolytic activity: alpha hemolysis (greenish hue); beta hemolysis (clear zone); upsilon hemolysis (no hemolysis)
• Lancefiled serology groupings: polysaccharides; beta hemolytic streps are in Groups A and B

Question 8

Group A Beta-hemolytic: S. pyogenes

Answer 8

• Gram (+) cocci
• Virulence factors: nonimmunogenic hyaluronic acid; M-protein cell wall (non-infectious w/out it); Pyrogenic exotoxins (superantigens) & C5a peptidase
• Clinical significance: acute pharyngitis (strep throat), GAS (w/or w/out necrosis), streptococcal toxic shock syndrome.

Question 9

Group B Beta-hemolytic: S. agalactiae

Answer 9

• Commonly found in vaginal tract
• Transmission from mother to newborn during birth
• LEADING CAUSE OF NEONATAL SEPTICEMIA AND MENENGITIS
• Prophylactic antibiotic treatment reduces S. agalactiae sepsis

Question 10

Streptococcus pneumoniae (Pneumococcus)

Answer 10

• Gram (+) diplococcus, alpha-hemolytic
• Virulence factors: Capsule; Pili; Autolysins; Pneumolysins
• Clinical significance: Most common cause of COMMUNITY ACQUIRED PNEUMONIAS

Question 11

Enterococci

Answer 11

• E. faecium and E. Fecalis
• Can be alpha, beta, gamma hemolytic
• Normal fecal flora
• Cause of nosocomial infections w/antibiotic resistance