1. Streptococcus
Gram+ cocci
In chains

2. Streptococci Gram positive cocci in chains
Lancefield groups (A-S), classification system based on serology against bacterial antigens
We will use group A and D Streptococcus in lab
Some streptococci have been lumped in to other groups by areas they tend to colonize.
Viridans Streptococcus and Enterococcus

3. Pneumococcus
S. pneumoniae: pneumonia, ear infection, sinusitis,
most common cause of bacterial meningitis
Viridans
S. mitis: found on surface of inner cheek,
can cause endocarditis
Group A Strep
S. Pyogenes: skin and throat infections,
necrotizing fasciitis,
scarlet fever, toxic shock syndrome,
post infection- rheumatic fever, glomerulonephritis
S. Faecalis: Enterococcus as of 1984
Commensal inhabiting GI tract
Found in probiotic foods
Found in root canal treated teeth
Can cause endocarditis
VRE – Vancomycin Resistant Enterococcus
Life threatening nosocomial infections
Group D Strep

4. Blood Agar
Blood agar, an enriched media, used for the cultivation of fastidious organisms
Serves as a differential media used to detect the presence of organisms that produce hemolysins that destroy red blood cells.
Allows differentiation of organisms via differential hemolysis.

5. Three Categories of Hemolysis
alpha hemolysis—incomplete hemolysis; oxidizes the iron in hemoglobin producing a “greenish” discoloration on blood plates
beta hemolysis—complete destruction of red blood cells; results in clearing around growth
gamma hemolysis—no hemolysis; results in no change in the media
Beta Alpha Gamma

6. Hemolysis Aids in Classification

7. Pneumococcus Viridans Group A Strep Group D Strep
S. pneumoniae
Alpha hemolytic
Viridans
S. mitis
Alpha hemolytic
Group A Strep
S. pyogenes
Beta hemolytic
Further testing facilitates distinguishing among organisms and provides supporting evidence
Group D Strep
S. faecalis
Alpha / Gamma hemolytic

8. Bacitracin Test
Used to identify Group A, beta hemolytic Streptococci (S. pyogenes)
Bacitracin (antibiotic) inhibits bacterial cell wall synthesis
A zone of inhibition surrounding the disc indicates a Group A Strep (positive test result)

9. Bacitracin Test Results
Positive Result for Bacitracin Sensitivity

10. Bile Esculin Test Identification of Group D Streptococci
S. faecalis a.k.a E. faecalis
Medium contains bile, esculin and iron salts
In the presence of bile, Group D organisms hydrolyze esculin which reacts with the iron salts to form a brownish-black discoloration of the medium (positive result)

11. Bile Esculin Test Identification of Group D Streptococci
S. faecalis a.k.a E. faecalis
A brownish-black discoloration indicates a positive result
Tube 1 positive
Tube 2 negative

12. SF Broth (S. Faecalis Broth)
Another test used to identify
Group D Streptococci
Broth contains 6.5% NaCl (selective), glucose (differential) and a pH indicator
Group D Enterococci ferment the glucose; causing pH to drop and the pH indicator changes from purple to a “yellowish” color.

13. Optochin Sensitivity Test
Used to differentiate S. pneumoniae from other alpha hemolytic streptococci
S. pneumoniae is the only streptococcus susceptible to
small concentrations of the
antibiotic optochin (P disk)
A zone of inhibition indicates a positive result
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14. Pneumococcus
S. pneumoniae
Alpha hemolytic
Optochin sensitive
Viridans
S. mitis
Alpha hemolytic
Optochin resistant
Group A Strep
S. pyogenes
Beta hemolytic
Bacitracin sensitive
Group D Strep
S. faecalis
Alpha / Gamma hemolytic
+ Bile Esculin Test
+ SF