Streptococcus Health Dictionary

Streptococcus is a variety of gram-positive bacterium (see GRAM’S STAIN; BACTERIA) which under the microscope has much the appearance of a string of beads. Most species are saprophytic (see SAPROPHYTE); a few are PATHOGENIC and these include haemolytic types which can destroy red blood cells in a culture of blood agar. This o?ers a method of classifying the varying streptococcal strains. Alphahaeomolytic streptococci are usually associated with bacterial ENDOCARDITIS. SCARLET FEVER is caused by a ?-haeomolytic streptococcus called S. pyogenes. S. pneumoniae, also called PNEUMOCOCCUS, causes respiratory-tract infections, including PNEUMONIA. S. pyogenes may on its own, or with other bacteria, cause severe NECROTISING FASCIITIS or CELLULITIS in which oedema and death of subcutaneous tissues occur. The infection can spread very rapidly and, unless urgently treated with ANTIBIOTICS and sometimes surgery, death may quickly result. This spread is related to the ability of S. pyogenes to produce toxic substances called exotoxins. Although drug-resistant forms are occurring, streptococcal infections usually respond to treatment with antibiotics.

n. a genus of Gram-positive nonmotile spherical bacteria occurring in chains. Most species are saprophytes; some are pathogenic. Many pathogenic species are haemolytic, i.e. they have the ability to destroy red blood cells in blood agar. This provides a useful basis for classifying the many different strains. Strains of S. pyogenes (the ?-haemolytic streptococci) are associated with many infections, including *scarlet fever, and produce many *exotoxins. Strains of the ?-haemolytic streptococci are associated with bacterial *endocarditis. The species S. pneumoniae (formerly Diplococcus pneumoniae) – the pneumococcus – is associated with serious diseases, including pneumonia, pneumococcal *meningitis, and septicaemia; it is also a common bacterial cause of ear infections (see also pneumococcal vaccine). It occurs in pairs, surrounded by a capsule (see quellung reaction). S. mutans has been shown to cause dental caries. See also Lancefield classification; streptokinase. —streptococcal adj.