A bacterium with a rounded or spherical shape. Cocci may be true spheres (e.g. staphylococci), helmet-shaped (e.g. pneumococci), or kidney-shaped (e.g. Neisseriae). They may occur alone, in pairs, or in groups. If found in pairs they are called diplococci, threes are a triad, etc. Other group types include: tetracoccus (groups of four), streptococcus (chains), sarcina (cubes of eight), and staphylococcus (irregular clusters). Diseases caused by cocci include pneumonia, tonsillitis, bacterial heart disease, meningitis, septicemia (blood poisoning), and various skin diseases.
