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 Some streptococci have been lumped in to other groups by areas they tend to colonize. Viridans Streptococcus and Enterococcus

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

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.

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

Hemolysis Aids in Classification

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

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)

Bacitracin Test Results Positive Result for Bacitracin Sensitivity

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)

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

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.

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

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