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Back to Bacteria Index
Streptococcus
Streptococci are gram positive cocci arranged in chains. They are
widely distributed in nature, some are commensals in the body.
Classification
Streptococci are heterogenous group and are classified according to
their O2 requirements into obligate anaerobes (peptostreptococci) and
facultative anaerobes.
Facultative anaerobes can survive in the presence of O2. They are
subdivided according to their action on red cells in blood agar into:
Beta hemolytic streptococci produce complete hemolysis and a clear
zone around the colonies e.g. streptococcus pyogenes.
Alpha hemolytic streptococci produce partial hemolysis with a zone
of greenish discoloration e.g. streptococcus viridans.
Non-hemolytic or gamma streptococci which cause no hemolysis or
change in RBCs e.g. streptococcus faecalis (enterococci).
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