(Science: bacteria, organism) A genus of bacteria that are gram-positive cocci, often occurring in chains of varying length. Some pathogenic species produce exotoxins. In man, streptococcal species are responsible for numerous infections such as scarlet fever, tonsillitis, erysipelas (skin infection), endocarditis, rheumatic fever, glomerulonephritis, impetigo, pneumonia, meningitis, pharyngitis, lymphadenitis and wound infections. Streptococcus pneumoniae is the main culprit in lobar and bronchopneumonia.
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. Haemolytic streptococci (viridans streptococci) produce limited haemolysis on blood agar, include streptococcus mutans, streptococcus salivarius and streptococcus pneumoniae. Beta haemolytic streptococci, of which streptococcus 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. Alpha streptococci are nonhaemolytic (e.g. Streptococcus faecalis).