Staphylococcus and Streptococcus Part 2

Question 1

What are the S. aureus enzymes?

Answer 1

1. Coagulase: Converts fibrinogen to fibrin; Makes clots
2. Catalase
3. Staphylokinase/Fibrinolysin: Dissolves clots (spreading factor)
4. Hyaluronidase: Hydrolyzes CT (Spreading factor, carbon source)
5. Penicillinase (Beta-lactamase)
6. DNAse, proteases, lipases

Question 2

What is S. aureus’ resevoir?

Answer 2

Human anterior nasopharynx, skin; Normal microbiota. Usually in hair follicles and sweat glands. Transmission by direct contact or aerosol

Question 3

How does S. aureus attach to surfaces?

Answer 3

Fibronectin, collagen, elastin binding proteins; Receptors for sialoprotein and laminin.

Question 4

Describe a S. aureus infection clinically.

Answer 4

Pyogenic, acute, aggressive and locally destructive; Presents with biols, folliculitis. impetigo, TSS, SSS and food poisoning.

Question 5

Describe TSS

Answer 5

No bacteremia, systemic toxin release; Presents with fever, rash and hypotension

Question 6

Describe SSS

Answer 6

Large cutaneous blisters, complete dequamation of epithelium; Recovery following antibody production

Question 7

Describe Staphylococcal food poisoning.

Answer 7

Ingestion of organism is not necessary; Rapid onset with vomiting, diarrhea, nausea but no fever.

Question 8

What are the systemic infections of S. aureus?

Answer 8

Osteomyelitis, septic arthritis, endocarditis, pneumonia, and empyema.

Question 9

How is virulence regulated in S.aureus?

Answer 9

Expression is controlled by cell density; Rna poly 3

Question 10

How does S. aureus evade the host immune system?

Answer 10

1. Leukocidins and hemolysins kill phagocytic cells.
2. Protein A blocks antibody function and titrates complement.
3. Catalase
4. Staphyloxanthin: carotenoid pigment protects against ROS

Question 11

How is S. aureus diagnosed?

Answer 11

Organism is cultured and identified; yellow on mannitol fermenter, catalase and coagulase positive.

Question 12

How is S. aureus treated?

Answer 12

Vancomycin; Most strains are now penicillin resistant. mecA encodes a PBP2’ to penicillin and other beta-lactams.

Question 13

Describe S. pyogenes.

Answer 13

Gram+, strictly fermentative, catalase negative; Common cause of pharyngitis and tonsillitis

Question 14

How are Streptococci classified?

Answer 14

1. Antigenic differences
2. Hemolysis pattern: alpha is partial lysis, beta is complete lysis of rbcs, and gamma is non-hemolytic
3. Biochemical/Physiological differences

Question 15

What are the 3 types of disease sS. pyogenes causes?

Answer 15

1. Direct invasion:pharyngitis, skin or wound infections.
2. Toxin mediated: TSS, scarlet fever, fascitis.
3. Delayed immunologic reaction: Rheumatic fever, glomerulonephritis.

Question 16

What are the surface antigens on S. pyogenes?

Answer 16

Hyaluronic acid capsule, lipoteichoic acid, and M protein.

Question 17

What role does M protein play?

Answer 17

Forms protective coat of fibrin and fibrinogen, degrades C3b, binds IgM

Question 18

What toxins does S. pyogenes have?

Answer 18

1. Streptolysin: oxygen liable, pore forming cytolysin for rbcs, wbcs.
2. Extracellular enzymes: Streptokinases (fibrinolysin), hyaluronidase, C5a peptidase, DNAses

Question 19

What is S. pyogenes resevoir?

Answer 19

Human nasopharynx; Transmission by direct contact or aerosol. Attachment initially by lipotechoic acids via fibronectin.

Question 20

What happens if S. pyogenes releases erythrogenic toxin?

Answer 20

Scarlet fever; Usually a couple days after pharyngitis symptoms. Can get sequelae due to delayed immune reaction; Glomerulonephritis, rheumatic fever.

Question 21

What are some S. pyogenes diseases?

Answer 21

Impetigo, Erysipelas, necrotizing fascitis, TSS, rheumatic fever

Question 22

Describe Necrotizing fascitis.

Answer 22

Deep subcutaneous infection, destruction of fat and muscle; Starts like cellulitis but gets worse.

Question 23

How is S. pyogenes TSS different from S. aureus?

Answer 23

S. pyogenes TSS is systemic; Production of pyrogenic exotoxin.

Question 24

How is rheumatic fever caused?

Answer 24

Antibody to bacteria cross reacts with heart tissue; Type 2 hypersensitivity. Chronic and progressive damage. Usually following strep throat, not skin infection.