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Clinical Microbiology(MLCM- 201)
Prof. Dr. Ebtisam.F. El Ghazzawi.
Medical Research Institute (MRI) Alexandria University
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OUTCOMESBy the end of this lecture the Student should be able to understand Streptococci Types ,Shape Characteristics, pathology and Diagnosis.
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The streptococci are gram-positive catalase negative
spherical bacteria that characteristically form pairs or
chains during growth.
They are widely distributed in nature.
Some are members of the normal human flora, others
are associated with important human diseases.
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Streptococcus pyogenes Gram stain
Streptococcus pneumoniae Gram stain
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One of the most important characteristics for One of the most important characteristics for
identification of streptococci is the type of identification of streptococci is the type of
hemolysis:hemolysis:
Alpha-hemolytic streptococci form a green zone
around their colonies as a result of incomplete
lysis of red blood cells in the agar.
Alpha hemolysis and beta hemolysis on blood agar
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Beta-hemolytic streptococci form a clear zone around
their colonies because complete lysis of the red cells
occurs. Beta-hemolysis is due to the production of
enzymes (hemolysins) called Streptolysin O and
Streptolysin S.
Some streptococci are nonhemolytic (gamma hemolysis).
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Sheptococci cause a wide variety of infections.
Strept. Pyogenes (group A streptococci) is a
leading bacterial cause of pharyngitis and
cellulitis.
It is an important cause of impetigo, streptococcal
toxic shock syndrome, rheumatic fever and acute
glomerulonephritis.
Viridans group streptococci are the most common
cause of endocarditis.
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a. Specimens: specimens to be obtained depend
upon the nature of the streptococcal infection. A
throat swab, pus or blood is obtained for culture.
Serum is obtained for antibody determinates.
b. Smears: smears from pus often show single cocci
or pairs rather than definite chains. Smears of
throat swabs are rarely contributory, because
viridians streptococci are always present and
have the same appearance as group A
streptococci on stained smears.
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c. Culture: streptococci are cultured on blood
agar. Incubation in 10% CO2 often speeds
hemolysis. The degree and kind of hemolysis
(and colonial appearance) may help place an
organism in a definite group. Streptococci
belonging to group A may be presumptively
identified by inhibition of growth by Bacitracin.
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d. Antigen detection tests: Several commercial kits
are available for rapid detection of group A
streptococcal antigen from throat swabs. These
kits use enzymatic or chemical methods to extract
the antigen from the swab, then use EIA or
agglutination tests to demonstrate the presence of
the antigen.
e. Serologic tests: A rise in the titer of antibodies to
many group A streptococci antigen can be
estimated. Of these antibodies the antistreptolysin
O (ASO) particularly in respiratory disease can be
estimated.
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Assignments
scarlet Fever ß-Hemolytic Streptococci.
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QuestionsComplete the following-:
The streptococci are gram-positive ……………negative ……………bacteria.
Beta-hemolysis is due to the production of enzymes (hemolysins) called.………………
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Recommended Textbooks
Manual of Clinical Microbiology, Vols. 1 and 2: Eighth Edition Patrick R. Murray
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