False-color scanning electron micrograph (SEM) showing a culture of Streptococci bacteria. Streptococcus is a genus of Gram-positive, non-motile, spherical bacteria that typically form chains. Although most are saprophytes (feed on dead and decaying matter), some are parasites of humans and animals. They also contribute as commensals to the normal, healthy flora of human respiratory, alimentary (gut) and female genital tracts. The pathogenic species include: S. pneumoniae causing pneumonia of the lungs and S.pyogenes which accounts for the high incidence of sore throats and tonsillitis in young children. Magnification unknown.