Streptococci are chain forming cocci which are gram positive with shape extending from ovoid to spherical. They are mainly facultative anerobes. Most of pathogenic streptococci in human belong to the β hemolytic cluster and can be classified into Lancefield groups A, B,C, and G.
Others are α (e.g. Streptococcus pneumoniae) and γ hemolytic streptococci.