Royalty free and rights managed images of Streptococcus bacteria. Streptococcus is a genus of coccus (spherical) Gram-positive bacteria. These bacteria generally grow in chains or pairs because cell division in these bacteria occurs along one axis. There are over 50 species of Streptococcus bacteria, some of which cause disease in humans. Images include bacterial cultures in petri dishes, illustrations and diagrams, as well as light micrographs, scanning electron micrographs (SEMs), and transmission electron micrographs (TEMs).