Download Clinical Microbiology

Clinical Microbiology
(MLCM- 201)
Prof. Dr. Ebtisam.F. El Ghazzawi.
Medical Research Institute (MRI)
Alexandria University
OUTCOMES
By the end of this lecture the Student should be
able to understand Streptococci Types ,Shape
Characteristics, pathology and Diagnosis.
The
streptococci
catalase negative
are
gram-positive
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.
Streptococcus pyogenes
Gram stain
Streptococcus pneumoniae
Gram stain
One of the most important characteristics for
identification of streptococci is the type of
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
 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
hemolysis).
are nonhemolytic (gamma
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.
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
streptococci on stained smears.
as
group
A
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.
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.
Assignments
scarlet Fever ß-Hemolytic Streptococci.
Questions
Complete the following :-
The streptococci are gram-positive
……………negative ……………bacteria.
Beta-hemolysis is due to the production of
enzymes (hemolysins) called ……………….
Recommended Textbooks
Manual of Clinical Microbiology, Vols. 1 and 2:
Eighth Edition Patrick R. Murray