Streptococcus sp. bacteria. Coloured scanning electron micrograph (SEM) of Streptococcus sp. bacteria. These cells were cultured from a sample taken from a patient with a throat infection. Streptococcus sp. bacteria are spherical, Gram- positive cells. Many live as parasites in the respiratory and digestive systems of humans and animals, where they may cause disease. Magnification: x40,000 at 35mm size.