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Streptococcus

Streptococcus. Gram+ cocci In chains. 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

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Streptococcus

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  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 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 Page 166

  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

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