Pathogenicity of streptococci

Pathogenicity of streptococci

1. Streptococci are gram positive bacteria that grow in pairs or chains. They are classified on the basis of their pattern of hemolysis on blood agar.
• α (partial or green hemolysis)
• β (complete or clear hemolysis)
• γ (no hemolysis, rarely pathogenic)

2. β hemolytic str. are grouped by carbohydrate antigens:-
• Streptococcus pyogenes causes pharyngitis, scarlet fever, impetigo, rheumatic fever, toxic shock syndrome and glomerulonepheritis.
• Streptococcus agalactiae colonizes the female genital tract and causes chorioamnionitis in pregnancy as well as neonatal sepsis and meningitis.

3. α hemolytic str. Include:-
• S. pneumonia, a common cause of adult community acquired pneumonia and meningitis.
• Str. Mutants/viridans-group str. , a normal component of oral flora can cause dental caries and endocarditis

4. Streptococcal infections are characterized by diffuse interstitial neutrophilic infiltrates with minimal host tissue destruction.


Str.- streptococcus/streptococci


Tiana Alexander
2006MO33