Streptococcus pyogenes (group A β-hemolytic Streptococcus) is a bacteria that is the most common bacterial cause of a sore throat (pharyngitis).  Streptococcus pyogenes infection can lead to scarlet fever or, if not treated, rheumatic fever.  Strep pharyngitis is uncommon in children under 2 years old.  Pharyngitis is spread from person-to-person and is most common in the Winter and Spring when children spend more time indoors with other potentialy-infected children.

Diseases

• Strep throat (pharyngitis)
• Otitis media
• Sinusitis
• Mastoiditis
• Meningitis
• Bacterial skin infections
• Scarlet fever (caused by a toxin produced by Streptococcus pyogenes)
• Rheumatic fever (caused by a late immune response to Streptococcus pyogenes)
• Acute glomerulonephritis - kidney inflammation (caused by a late immune response to Streptococcus pyogenes)

Habitat and Transmission

• Found on the skin and inside the nose, mouth and throat in small numbers
• Produces disease when it gains access to the blood and tissues
• Spread from person to person in respiratory secretions

Weapons and Defenses

• M protein - a protein on the outside of the bacteria that interferes with phagocytosis (destruction by white blood cells).  There are around 80 known strains of Streptococcus pyogenes, each with it's own M protein and serotype. 
• Pili - allow attachment of the bacteria to human mucous membranes (such as the inside of the throat).
• Streptokinase - an enzyme that dissolves blood clots
• DNase - breaks down human DNA.  Antibody to this component can be used for diagnosis of infection (nti-DNase B titer).
• Hyaluronidase - breaks down connective tissue, allowing spread of the bacteria in skin infections
• Erythrogenic toxin - causes the rash of scarlet fever
• Streptolysin O - breaks down red blood cells.  Antibody to this component can be used for diagnosis of infection (ASO titer).
• Streptolysin S - breaks down red blood cells
• Pyrogenic endotoxin A - causes inflammation
• Exotoxin B - causes tissue destruction.  Found in strains that cause necrotizing fascititis. 

Weaknesses

• Infection with Streptococcus pyogenes leads to the production of antibodies against the specific serotype (based in part on the M protein).  This leads to immunity and protection against re-infection with that serotype.  Unfortunately, there are approximately 80 known serotypes, so re-infection is possible with a different strain.
• Streptococcus pyogenes is sensitive to antibiotics such as penicillin, amoxicillin, erythromycin or azithromycin.
  

  

Photo - Note the inflammation of the oropharynx and petechiae, or small red spots on the soft palate caused by Strep Throat.CDC/Dr. Heinz F. Eichenwald. 1958. Used with permission.

Photo 2 - A photomicrograph of Streptococcus spp. bacteria using Gram stain technique. CDC. 1970. Used with permission.

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