Streptococcus Pyogenes

Question 1

1) classification

Answer 1

Family: streptococcaceae
Genus: streptococcus
Species: pyogenes

Beta hemolytic streptococcus- group A

Consist of 1 species with 40 antigenic types

5 - 15% of normal individual habour it in their respiratory tract without symptoms

Question 2

2) morphology

Answer 2

• gram positive cocci
• arranged in chain
• some strains are capsulated

Question 3

3) growth characteristics

Answer 3

• facultative anaerobes

- non-fastidious

Question 4

4) antigenic structure

Answer 4

-Most S.pyogenes contain A antigens
-Most produce capsule composed of hyaluronic acid
-Cell wall consist of:
Protein (R,T,M antigens)
Peptidoglycan
Carbohydrate (group specific)
-Pili (composed of M protein)
Covered with lipoteichnoic acid

Question 5

5) virulence factors

Answer 5

Toxins
Pyogenic exotoxin:

• causes streptococcal toxic shock syndrome
• scarlet fever

Hemolysins:
-streptolysin O (O2 labile)
Pathogenic
Stimulate production of ASO

• streptolysin S (O2 stable)
  Nonpathogenic
  Doesn’t produce antibodies
  Responsible for RBC hemolysis

Enzymes

Hyaluronidase
Deoxyribonuclease
Streptokinase (fibronolysis)

Question 6

6) disease

Answer 6

Local infections:

• streptococcal sore throat
• scarlet fever pyoderma (rash and fever)

Invasive infections:
Erysipelas
Puerperal fever
Sepsis

Fulminant infections and streptococcal toxic shock syndrome

Poststreptococcal (nonsupurative) diseases:

Acute glomerulonephritis
Rheumatic fever- is the most dangerous

Damages heart muscle and valves

Question 7

7) microbiological diagnosis

Answer 7

BAP: small colonies surrounded by large beta hemolytic zone

Specific tests:
Catalase negative
Bacitracin : susceptible
CAMP test: negative

Serological rest:
Determination of ASO (antisteptolysin O antibodies)

Question 8

8) treatment and prevention

Answer 8

• all are susceptible to penicillin G

- for allergic patients, macrolides such as erythromycin or clindamycin