Corrynebacterium diphteriae, also known as the Klebs-Löffler bacillus, belongs to the bacteria family Corynebacteriaceae, genus Corynebacterium. Corrynebacterium diphteriae is classified into four biotypes according to their colony morphology: C. d. mitis, C. d. gravis, C. d. intermedius, and C. d. belfanti. Corrynebacterium diphteriae can produce diphtheria toxin, which inactivates the elongation factor EF-2 to alter protein function in the host. This leads to a pharyngitis and 'pseudomembrane' in the throat. Corrynebacterium diphteriae infects the nasopharynx or skin and causes diphtheria, a common paradigm of the toxigenic infectious diseases.