A variety of gram-positive bacterium (see GRAM'S STAIN; BACTERIA) which under the microscope resembles a string of beads. Some are PATHOGENIC (cause disease), including haemolytic types, so called because they can be seen in a culture of blood AGAR to destroy red blood. This offers a method of classifying the varying streptococcal strains. Alpha-haemolytic streptococci are usually associated with bacterial ENDOCARDITIS. SCARLET FEVER is caused by a β-haemolytic 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. It may spread rapidly, related to the ability of S. pyogenes to produce toxic substances called exotoxins. Many streptococci can be treated with PENICILLIN but increasing resistance has meant that other antibiotics may be needed.