Staphs and Streps
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Transcript Staphs and Streps
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
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