Diphtheria bacterium. Coloured transmission electron micrograph of Corynebacterium diphtheriae bacterium in the human throat. This Gram-positive rod-shaped bacterium, sectioned through, causes diphtheria. Here, it is seen adhering to the surface of an epithelial cell (lower frame) of the throat. C. diphtheria is generally located in the throat, but may affect other mucous membranes and the skin. The throat passage may be constricted, impeding normal breathing. The multiplying bacteria release toxins into the bloodstream that damage the heart and nerves. Treatment is with antitoxin & penicillin. Vaccination is available. Magnification: x36,000 at 6x4.5cm size.