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.
Fig. 1 Corynebacterium diphtheriae
Diphtheria is an infection of upper respiratory tract. Its symptoms include sore throat, fever, and malaise. A thick, gray-green fibrin membrane, the 'pseudomembrane', can be found at the site where infection occurs. The form of this 'pseudomembrane' can be considered as a combined effects of bacterial growth, toxin production, host immune response, and the necrosis of underlying tissue. In the field of clinic, diphtheria can be classified into two types: nasopharyngeal and cutaneous. Symptoms of the pharyngeal diphtheria vary from pharyngitis to hypoxia because of airway obstruction by the 'pseudomembrane'. In a case of cutaneous diphtheria, the 'pseudomembrane' is gray-brown and it covers the skin lesions. Systemic complications that are life-threatening may occur as a result of the action of diphtheria toxin on peripheral motor the myocardium and neurons, such as loss of motor function and congestive heart failure.
Corrynebacterium diphteriae is a Gram-positive, nonmotile, club-shaped, noncapsulated bacillus. The genome of Corrynebacterium diphteriae contains a single circular chromosome with the size of 2.5 Mbp, without any plasmids. Strains of Corrynebacterium diphteriae growing in tissue, or some older cultures in vitro, contains some thin spots in the cell wall that may lead to a decolorization during the Gram stain. Thus, it may result in a Gram-variable reaction. The bacterium spreads by droplets, secretions, or direct contact. Most strains of Corrynebacterium diphteriae require pantothenic acids and nicotinic for growth; some also require biotin, thiamine, or pimelic acid. Corrynebacterium diphteriae is sensitive to the majority of antibiotics, such as the penicillins, cephalosporins, ampicillin, quinolones, tetracyclines, chloramphenicol, cefuroxime, and trimethoprim.
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