Corynebacterium diphtheriae

Corynebacterium diphtheriae

Organism

Corynebacterium diphtheriae is an irregular staining, pleomorphic, bacillus.
Although they stain gram-positively with short chains in "V," "Y," or "Chinese letter" configuration, they do not have a typical gram-positive cell wall. Their cell wall contains arabinose, galactose, diaminopimelic acid, and short chain mycolic acids
A nonmotile, facultative anaerobe (def).

Habitat

Humans are the only known reservoir; carried in the oropharynx (def) or on the skin.

Source

Spread person to person by contact with respiratory droplets or skin lesions.

Epidemiology

Worldwide in unvaccinated hosts or asymptomatic carriers.
Very rare in developed countries where children are routinely vaccinated against diphtheria.

Clinical Disease

Respiratory diphtheria develops after a 2-6 day incubation period. Symptoms include malaise, pharyngitis, and low-grade fever. A thick pseudomembrane composed of bacteria, plasma cells (def), lymphocytes (def), fibrin, and dead cells develops and covers the tonsils, uvula (def), and palate (def); may extend down to the larynx or up into the nasopharynx. Complications in severe disease include breathing obstruction, cardiac arrhythmia (def), coma, and death.
Cutaneous anthrax appears as a papule (def) that develops into a chronic, nonhealing ulcer (def) occasionally covered by a grayish membrane.

Pathogenicity

Corynebacterium diphtheriae produses diphtheria exotoxin. This toxin interferes with host cell protein synthesis by catalyzing the ADP-ribosylation of host cell elongation factor 2 (EF-2), necessary in order for tRNA to insert new amino acids into the growing protein chain. This results in cell death. Cells of the heart, nerve tissue, and kidneys have receptors for this exotoxin.

Treatment

The disease is prevented by active immunization (def) with diphtheria toxoid (def), the "D" portion of the DTP vaccine, stimulates the body to make neutralizing antibodies against the binding component of the diphtheria exotoxin. Once the antibody binds to the exotoxin, the toxin can no longer bind to the receptors on the host cell membrane.
The disease can also be treated or prevented by passive immunization (def) with diphtheria immune globulin (def) to neutralize the diphtheria toxin.
Treatment with penicillins or erythromycin (see antibiotic table) can be used to elimate the Corynebacterium diphtheriae from the body.

*Drugs may change with time.

For a more detailed article on Corynebacterium diphtheriae, see Corynebacterium Infections , by Lynda A Frassetto, MD, Associate Clinical Professor, Department of Internal Medicine, University of California at San Francisco School of Medicine; and Lynda A Frassetto, MD, is a member of the following medical societies: American College of Physicians, and American Society of Nephrology.