head picture
PYR test
microscope picture gram positive cocci in chains

Streptococcus pyogenes

PYR test

Unlike other beta-hemolytic streptococci isolated from human clinical specimens S.pyogenes produces an enzyme pyrrolidonyl aminopeptidase (PYR). Beta-hemolytic strains of enterococci might be confused with S.pyogenes (rare, enterococci are typically non-hemolytic or alpha-hemolytic, see here).

Microscopy:
Spherical or ovoid cells in chains of short to medium length (4-10 cells).
 

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