Beta-hemolysis of Group A streptococci (S.pyogenes) on agar plate with sheep blood

beta hemolysis, beta-hemolytic colonies on agar plate

Beta and gamma-hemolysis on sheep blood agar. Beta-hemolytic streptococci of Group A (Streptococcus pyogenes) are surrounded by zones of complete hemolysis (beta-hemolysis). Cultivation 48 hours in an aerobic atmosphere, 37°C.

Group A Streptococcus (S.pyogenes) is a bacterium often found in the throat and on the skin. People may carry group A streptococci in the throat or on the skin and have no symptoms of illness. Most GAS infections are relatively mild illnesses such as "strep throat", or impetigo. Occasionally these bacteria can cause severe and even life-threatening diseases.

Infection with GAS can result in a range of symptoms:

  • No illness
  • Mild illness (strep throat or a skin infection such as impetigo)
  • Severe illness (necrotizing faciitis, streptococcal toxic shock syndrome)
Severe, sometimes life-threatening, GAS disease may occur when bacteria get into parts of the body where bacteria usually are not found, such as the blood, muscle, or the lungs. These infections are termed "invasive GAS disease." Two of the most severe, but least common, forms of invasive GAS disease are necrotizing fasciitis and streptococcal toxic shock syndrome (STSS). Necrotizing fasciitis (occasionally described by the media as "the flesh-eating bacteria") destroys muscles, fat, and skin tissue. Streptococcal toxic shock syndrome, causes blood pressure to drop rapidly and organs (e.g., kidney, liver, lungs) to fail. STSS is not the same as the "toxic shock syndrome" frequently associated with tampon usage.