- Streptococcus
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Genus of Gram positive cocci that grow in chains. Some species ( Strep. pyogenes in particular) are responsible for important diseases in humans (pharyngitis, scarlet fever, rheumatic fever) : Strep. pneumoniae is the main culprit in lobar- and broncho-pneumonia. Streptococci have anti-phagocytic components (hyaluronic acid-rich capsule and M-protein), and release various toxins (streptolysins O and S, erythrogenic toxin) and enzymes (streptokinase, streptodornase, hyaluronidase, and proteinase). a -haemolytic streptococci (viridans streptococci) produce limited haemolysis on blood agar; include S. mutans, S. salivarius, S. pneumoniae. b -haemolytic streptococci, of which S. pyogenes is the only species, though there are many serotypes, produce a broad zone of almost complete haemolysis on blood agar as a result of streptolysin O and S release. g -streptococci are non-haemolytic (eg. S. faecalis ).
Dictionary of molecular biology. 2004.