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STREPTOCOCCI
The genus Streptococci
consists of chain forming Gram-positive cocci that facultative anaerobes
and some species are strict anaerobes (peptostreptococci). They grow on
blod agar and usually give better haemolytic reaction when incubated
anaerobically. Streptococci are catalase negative and this may
help to distinguish them from staphylococci.
CLASSIFICATION OF
STREPTOCOCCI
I. Beta-Haemolytic Streptococci (Facultative Anaerobes):
These are strains that produce soluble haemolysin, and have definite zone of clearing around colonies on blood agar (compelete disruption of erythrocytes, i.e. β-haemolysis).
II. Non-Beta-Haemolytic Streptococci (Facultative Anaerobes):
e.g. Viridans streptococci and Streptococcus pneumonia. They do not produce soluble haemolysin, they cause partial clearing and often green colouration, i.e. incompelete lysis of RBCs (α-haemolysis). Other are non-haemolytic, produce no obvious change on blood agar.
III. Peptostreptococci (Strict Anaeroes):
They grow under anaerobic conditions and produce variable haemolysis. They are members of the normal flora of the gut and female genital tract. They often participate in mixed anaerobic infections in the abdomen, pelvis, lung or brain. |
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STREPTOCOCCI
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