Streptococcus pyogenes
Kate Leeper

Streptococcus pyogenes is a spherical gram-positive bacterium and is classified as Group A streptococcus. Streptococcus pyogenes grow in long chains. The metabolism of S. pyogenes is fermentative; the organism is a catalase-negative facultative anaerobe, and requires enriched medium containing blood in order to grow. Group A streptococci usually are beta-hemolytic and also usually have a capsule composed of hyaluronic acid. Beta-hemolytic streptococci produce a toxin that forms a clear zone of hemolysis on blood agar, demonstrating its ability to destroy red blood cells. The hemolysis is accredited to toxins formed by Group A streptococci called streptolysins.  Streptolysins can destroy red blood cells and also the white blood cells accountable for fighting off bacteria and disease, among other body cells.

Streptococcus pyogenes is one of the most commonly occurring pathogens of humans. Approximately 5-15% of normal individuals harbor the bacterium, most commonly in the respiratory tract, without any signs of disease.  S. pyogenes can infect when defenses are compromised. When the bacteria are introduced or transmitted to vulnerable tissues, a variety of suppurative infections can occur. This bacterium is highly sensitive to the antibiotic penicillin. If the streptococcus is not treated with penicillin, failure to attain sufficient tissue levels in the pharynx could arise. Some strains of S. pyogenes have developed resistance, including clindamycin, macrolides, and tetracyclines.

S. pyogenes causes many different types of human diseases, varying from simple skin infections to deadly diseases. Most infections start in the skin or the throat. Mild infections can include pharyngitis (strep throat), and skin infections like impetigo. Cellulitis and Erysipelas can also occur, spreading to deep layers of the skin. One potentially deadly condition from Streptococcus pyogenes is necrotizing fasciitis, caused by the invasion and multiplication in the fascia. Necrotizing fasciitis requires surgery. Some strains of Streptococcus pyogenes are related to the release of bacterial toxins. This can lead to scarlet fever or life-threatening streptococcal toxic shock syndrome. S. pyogenes also causes rheumatic fever.

Streptococcus pyogenes also can cause post-infections “non- pyogenic” diseases. These are autoimmune mediated complications following a small percentage of infections, including acute poststreptococcal glomerulonephritis and rheumatic fever. Both of these conditions appear many weeks after the initial infection.  Acute glomerulonephritis can follow a skin infection or strep throat, and is the inflammation of the renal glomerulus. Rheumatic fever presents inflammation of joints and possibly heart inflammation following strep throat.

S. pyogenes is actually linked to OCD, obsessive-compulsive disorder and tic disorders in children. This, however, is still under consideration and is not proven yet.


Microbial Life


*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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