Streptococcus
Gram+ cocci
In chains
Streptococci
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



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
S. pneumoniae: pneumonia, ear infection, sinusitis,
most common cause of bacterial
meningitis
Pneumococcus
S. mitis: found on surface of inner cheek,
can cause endocarditis
Viridans
S. Pyogenes: skin and throat infections,
necrotizing fasciitis,
Group A Strep
scarlet fever, toxic shock syndrome,
post infection- rheumatic fever, glomerulonephritis
S. Faecalis:
Group D Strep
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
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
S. pneumoniae
Pneumococcus
Viridans
Alpha hemolytic
S. mitis
Alpha hemolytic
S. pyogenes
Group A Strep
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
S. pneumoniae
Pneumococcus
Viridans
Alpha hemolytic
Optochin sensitive
S. mitis
Alpha hemolytic
Optochin resistant
S. pyogenes
Group A Strep
Beta hemolytic
Bacitracin sensitive
S. faecalis
Group D Strep
Alpha / Gamma hemolytic
+ Bile Esculin Test
+ SF