Introduction
Streptococcus is a genus of gram-positive coccus (plural cocci), or spherical bacteria in the phylum Firmicutes. Cell division occurs along a single axis, so as they grow they tend to form pairs or chains that may appear bent or twisted. (it can divide along multiple axes, thereby generating irregular grape-like clusters of cells.) When alpha hemolysis is present, the agar under the colony will appear dark and greenish due to the conversion of hemoglobin to green biliverdin. In addition to strep throat, some certain species are responsible for many cases of pink eye, meningitis, bacterial pneumonia, endocarditis, erysipelas, and necrotizing fasciitis (the 'flesh-eating' bacterial infections). Many such invasive infections are of considerable public health importance; for example, worldwide, pneumococcal disease causes over 800 000 deaths in children under 5 years of age annually. However, sereval species are not pathogenic, and form part of the commensal human microbiota of the mouth, skin, intestine, and upper respiratory tract.