Streptococcus Infections

Streptococcus is a genus of spherical gram-positive bacteria. In these bacteria, cellular division occurs along a single axis, thus they grow in chains or pairs. Certain Streptococcus[Page 450]species are responsible for many diseases, including the common streptococcal pharyngitis (“strep throat”), meningitis, bacterial pneumonia, endocarditis, erysipelas, and necrotizing fasciitis. However, many streptococcal species are nonpathogenic. Streptococci are also part of the normal commensal flora of the mouth, skin, intestine, and upper respiratory tract of humans.

Individual species of Streptococcus are classified based on their hemolytic properties. Alpha hemolysis is caused by a reduction of iron in hemoglobin, giving it a greenish color on blood agar. Beta-only hemolysis is complete rupture of red blood cells, giving distinct, wide, clear areas around bacterial colonies on blood agar.

Group A streptococcal ...