Streptococcus Gram+ cocciIn 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

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

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

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

Hemolysis Aids in Classification

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

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.

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