Streptococci

Streptococci are gram-positive cocci. They may be divided into alpha and beta haemolytic types

Alpha haemolytic streptococci (partial haemolysis)

The most important alpha haemolytic Streptococcus is Streptococcus pneumoniae (pneumococcus). Pneumococcus is a common cause of pneumonia, meningitis and otitis media. Another clinical example is Streptococcus viridans

Beta haemolytic streptococci (complete haemolysis)

These can be subdivided into groups A-H. Only groups A, B & D are important in humans.

Group A

• most important organism is Streptococcus pyogenes
• responsible for erysipelas, impetigo, cellulitis, type 2 necrotizing fasciitis and pharyngitis/tonsillitis
• immunological reactions can cause rheumatic fever or post-streptococcal glomerulonephritis
• erythrogenic toxins cause scarlet fever

Group B

• Streptococcus agalactiae may lead to neonatal meningitis and septicaemia

Group D

• Enterococcus

Group B streptococcus bacteria. Credit: NIAID

Group A strep (Strep. pyogenes)

Toxins produced: