Strep throat, the most common form of Streptococcus pyogenes! I bet you've had it at least once.

Blood agar plate of Streptococcus pyogenes, by Dr. William Schwan, University of Wisconsin-La Crosse.

When you go in to see the doctor and they take a throat culture, they put the contents of the swab on a blood agar plate, just like the one above.  The appearance of this plate is from a special technique, streak plate method, which is used to isolate colonies of bacteria.  At the end of the blue arrow, you can see a colony of the Streptococcus pyogenes.  The white circular area around the bacteria is the beta hemolysis.  Beta hemolysis is seen as a complete clearing of the blood agar medium around the colonies.  The white area around the colony is the clearing from the Streptococcus pyogenes.   

Habitat:

• Pharynx

• Rectum

• Skin

Diseases:

• Acute endocarditis: an inflammation of the inner layer of the heart, the endocardium

• Cellulitis: an inflammation of the connective tissue underlying the skin

• Conjunctivitis: an inflammation of the conjunctiva (the outermost layer of the eye and the inner surface of the eyelids)

• Erysipelas: skin infection, resulting in inflammation and characteristically extending into underlying fat tissue

• Fasciitis: an inflammation of the fascia (specialized connective tissue layer which surrounds muscles, bones, and joints, providing support, protection and giving structure to the body)

• Glomerulonephritis: inflammation of the glomeruli

• Impetigo: a superficial skin infection

• Otitis media: an inflammation of the middle ear (the space behind the ear drum)

• Pharyngitis: a painful inflammation of the pharynx, and is colloquially referred to as a sore throat

• Pneumonia: an illness of the lungs and respiratory system in which the alveoli (microscopic air-filled sacs of the lung responsible for absorbing oxygen from the atmosphere become inflamed and flooded with fluid

• Rheumatic fever: an inflammatory disease which may develop after a Group A streptococcal infection (such as strep throat or scarlet fever) and can involve the heart, joints, skin, and brain

• Septicemia

• Wound infections (like necrotizing fasciitis)

This bacteria causes a ton of problems!

Streptococcus pyogenes is solely a pathogen of humans and is carried asymptomatically usually in the throat by 20-25% of the population (Hart 88).  It is spread person to person by respiratory droplets or by physical contact.  Penicillin is used as the treatment and unfortunately there is no vaccine available.  Fortunately, Streptococcus pyogenes is very sensitive to penicillin and have not become resistant or formed any antibiotic resistant mutants (O'Leary 103-104).  

Streptococcus pyogenes is one of the most common pathogens of soft tissue infections (Hawkey and Lewis 147-148).  The most frequent upper respiratory tract disease is a type of pharyngitis called strep throat, which is caused by Streptococcus pyogenes (Sankaran 234).  With repeated attacks of streptococcal sore throat a person can experience an increase in damage to their heart valves.

Information on this page is from Starr, Mortimer P (The Prokaryotes), Hart, Tony (Microterrors), O'Leary, William (Practical Handbook of Microbiology), Hawkey, Peter, Deirdre Lewis (Medical Bacteriology), and Sankaran, Neeraja (Microbes and People).