Possess granules (metachromatic granules) near the poles that give the rod a beaded appearance It tends to lie in parallel (pallisades) or at acute angles to one another in stained smears, forming V,L , W shapes, so called Chinese-character arrangement It has four four biotypes named as gravis, mitis, intermedius and balfanti based on growth characteristics and severity of disease produced Pathogenesis and clinical features: Found in nature in the respiratory tract, in wounds, or on the skin of infected person or normal carriers Spread by droplets or by direct contact The organism colonize the mucus membrane or skin abrasions and toxigenic C.diphteriae start producing exotoxin, possessing two components,fragment A and B. Fragment B transpots fragment A into the cell and fragment A inhibit polypeptide chain elongation by inactivating the elongation factor EF-2, required for translocation of polypeptidyl-tRNA from the acceptor to the donor site on the eukaryotic ribosome, leading to abrupt arrest of protein synthesis and result in cell necrosis and neurotoxic effect. Diphteria toxin causes respiratory tract epithelial destruction tesulting in formation of necrotic epithelium with pseudomembrane formation over the tonsils, pharynx, and larynx. Distant toxic damage includes parenchymal degeneration and necrosis in heart muscle, liver, kidney, adrenal glands and peripheral and cranial nerves. Wound/skin diphteria occurs chiefly in the tropics and forms membrane-covered wound that fails to heal. Systemic effect is negligible.