Download - Streptococcus
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Streptococcus Gram+ cocciIn chains
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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
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Pneumococcus
Viridans
Group A Strep
Group D Strep
S. pneumoniae: pneumonia, ear infection, sinusitis,
most common cause of bacterial meningitis
S. mitis: found on surface of inner cheek, can cause endocarditis
S. Pyogenes: skin and throat infections, necrotizing fasciitis,scarlet fever, toxic shock syndrome,
post infection- rheumatic fever, glomerulonephritis
S. Faecalis: Enterococcus as of 1984Commensal inhabiting GI tractFound in probiotic foodsFound in root canal treated teethCan cause endocarditisVRE – Vancomycin Resistant EnterococcusLife threatening nosocomial infections
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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.
Blood Agar
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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
Three Categories of Hemolysis
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Hemolysis Aids in Classification
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Pneumococcus
Viridans
Group A Strep
Group D Strep
S. pneumoniae Alpha hemolytic
S. mitisAlpha hemolytic
S. pyogenesBeta hemolytic
S. faecalisAlpha / Gamma hemolytic
Further testing facilitates distinguishing among organisms and provides supporting evidence
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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)
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Bacitracin Test Results Positive Result for Bacitracin
Sensitivity
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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)
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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
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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.
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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
Optochin Sensitivity Test
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Pneumococcus
Viridans
Group A Strep
Group D Strep
S. pneumoniae Alpha hemolyticOptochin sensitive
S. mitisAlpha hemolyticOptochin resistant
S. pyogenesBeta hemolyticBacitracin sensitive
S. faecalisAlpha / Gamma hemolytic+ Bile Esculin Test+ SF