Diphtheria bacteria. Coloured transmission electron micrograph (TEM) of Corynebacterium diphtheriae bacteria, cause of diphtheria. This section cuts through several bacterial cells. The nucleus (a spiral form) and cytoplasm are seen surrounded by a mucus cell wall (pink). C. diptheriae are rod-shaped bacilli bacteria which are usually found located in the human throat. Infection causes constriction in the throat passage, sore throat and fever. The bacteria release toxins into the blood that may damage the heart and nerves. Magnification: x24,