21 Jan

Streptococci

Streptococci differ from the staphylococci in two main ways: they occur in chains instead of clusters and they lack the enzyme catalase, which degrades hydrogen peroxide to form water and oxygen.  Streptococci oftentimes cause mixed infections with staphylococci , but they independently cause diseases such as pneumonia, meningitis, endocarditis, pharyngitis, crysipelas, and glomerulonephritis.  Streptococci are found in the human pharynx and mouth where they occur on the surfaces of the teeth, tongue, cheek, throat, and in saliva.  They can also be found on the skin.  The streptococci of the greatest medical importance to humans are S. pyrogenes, S. agalactiae, and S. pneumoniae.  In 1919 J.H. Brown proposed a way to classify streptococci.  His method was based on the ability of the organism to cause lysis of red blood cells when grown on blood agar.