Clinical Microbiology(MLCM- 201)

Prof. Dr. Ebtisam.F. El Ghazzawi.

Medical Research Institute (MRI) Alexandria University

OUTCOMESBy the end of this lecture the Student should be able to understand Streptococci Types ,Shape Characteristics, pathology and Diagnosis.

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.

Streptococcus pyogenes Gram stain

Streptococcus pneumoniae Gram stain

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

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).

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 as group A

streptococci on stained smears.

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.

QuestionsComplete 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