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Pathogen Page

Corynebacterium diphtheriae

I. General Information

1. NCBI Taxonomy ID:

2. Disease:

Diphtheria

3. Introduction

Corynebacterium diphtheriae is an aerobic Gram-positive bacterium that causes diphtheria in humans. Respiratory diphtheria is an upper respiratory tract illness characterized by a sore throat with low-grade fever and an adherent membrane of the tonsils, pharynx, or nose. Neck swelling is usually present in severe disease. Cutaneous diphtheria presents as infected skin lesions which lack a characteristic appearance (CDC: Diphtheria).

4. Microbial Pathogenesis

Diptheria as a disease presents itself in two forms: respiratory and cutaneous. Cutaneous diphtheria can be caused by both the toxigenic and the nontoxigenic strains of C. diphtheriae. Cutaneous diphtheria presents as nondescript sores or shallow ulcers on the skin, and is usually mild and treatable. Only 1-2% of cutaneous cases become toxigenic. Respiratory diphtheria is caused by C. diphtheriae bacteria adhering to and colonizing the tonsils, nasal cavity, and throat. Mechanisms of adherence are unknown, but recent research suggests that proteins SpaB and SpaC found on two minor pili play an important role in specifically binding to pharyngeal cells. A visible, leathery pseudomembrane forms over the surface of the cells, especially the tonsils and throat. A lesion develops and plasma from injured epithelial cells leaks into the lesion, producing a fibrin network infused with C. diphtheriae. Symptoms present themselves 2-5 days after infection with C. diphtheriae. Initially, symptoms include a sore throat and low fever. More severe symptoms include inflammation of the neck and difficulty breathing or asphyxiation (MicrobeWiki: C. diphtheriae).

5. Host Ranges and Animal Models

C. diphtheriae is only found in the mouth, throat, nose, skin, bodily secretions, and wounds of infected persons. Animals do not easily contract Diphtheria from human beings, and naturally have immunity (MicrobeWiki: C. diphtheriae).

6. Host Protective Immunity

Acquired immunity to diphtheria is due primarily to toxin-neutralizing antibody (antitoxin). Passive immunity in utero is acquired transplacentally and can last at most 1 or 2 years after birth. In areas where diphtheria is endemic and mass immunization is not practiced, most young children are highly susceptible to infection. Probably, active immunity can be produced by a mild or inapparent infection in infants who retain some maternal immunity, and in adults infected with strains of low virulence (inapparent infections) (Textbook of Bacteriology).

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