This document discusses the identification of Streptococcus bacteria from clinical specimens. It describes the characteristics of streptococci as gram-positive cocci that can appear in chains or pairs and are usually encapsulated. Sources of streptococcal specimens include the respiratory, gastrointestinal, and genitourinary tracts and skin. Identification methods mentioned include examining hemolysis on blood agar, gram stains showing streptococci in chains, optochin susceptibility testing for S. pneumoniae, bacitracin testing and rapid identification tests for S. pyogenes, and serological testing of antistreptolysin O titers.

1. Streptococcus
Lab 3
Prepared by
Samira Fattah
Assis. Lec.
College of health sciences-HMU

2. Characters of streptococci
• Gram positive cocci
• Chain or pair
• Usually capsulated
• Catalase negative(staphylococci are catalase positive)

4. Sources of the specimen
• Respiratory tract(RT)
• Gastrointestinal tract(GIT)
• Genitourinary tract(GUT)
• Skin

5. Hemolysis on Blood Agar
Hemolysis on BA
– -hemolysis
Partial hemolysis
Green discoloration around colonies
e.g. S. pneumoniae & S. viridans
– -hemolysis
Complete hemolysis
Clear zone of hemolysis around colonies
e.g. Lancefield Group A & B (S. pyogenes & S. agalactiae)
– -hemolysis
No hemolysis
e.g. Group D (Enterococcus sp.)

6. Streptococcus in chains (Gram stain)

7. Lab Identification of
Streptococcus pneumoniae
• Commonly referred to as pneumococcus
• Formerly Diplococcus pneumoniae

8. 8
Streptococcus pneumoniae (diplococcus). Fluorescent stain

9. Streptococcus pneumoniae
Diagnostic Laboratory Tests
• Optochin susceptability test

12. Lab Identification of
S. pyogenes (Group A)
•Catalase Negative: Differentiates from Staphylococcus
•Bacitracin test
•Rapid Identification Tests

14. •Rapid Identification Tests:
•Based on extraction of Group A carbohydrate directly from throat swabs.
ELISA, Coagglutination, Fluorescent Antibody

15. Post-infectious diagnosis (serology)
• Antistreptolysin O titer (ASOT):
latex agglutination test. A titer of 200 IU/ml or more is
significant.

17. API 20 Strep test