Diphtheria bacteria. Coloured transmission electron micrograph (TEM) of Corynebacterium diphtheriae bacteria, cause of diphtheria. The bacteria are club-shaped, Gram-positive, non- motile rods. They have a spiral nuclear region (red and orange in centre of bacteria) contained within cytoplasm (white speckled). Surrounding each cell is a mucus cell wall (red outlines). Diphtheria is caused by a potent exotoxin released from the bacterium. Symptoms include sore throat, fever and breathing difficulties. Exotoxin damage to the heart and nerves can occur. Treatment includes antitoxins, antibiotics and complete rest. Magnification x30,000 at 6x4.5cm size.