Corynebacterium diphtheriae

Dirty white pseudomembrane classically seen in diphtheria 2013-07-06 11-07

Corynebacterium diphtheriae is a species of bacteria that is pathogenic to humans and is the causative agent of diphtheria, a serious infectious disease primarily affecting the mucous membranes of the respiratory tract. The organism is named after the Greek word for leather, diphthera, referring to the characteristic appearance of the pseudomembrane that forms in the throat of those infected. This bacterium is part of the genus Corynebacterium, which encompasses a range of species, some of which are harmless, while others can cause disease.

Characteristics

Corynebacterium diphtheriae is a Gram-positive, non-motile, club-shaped bacterium. It is also known to form irregular or palisade arrangements during growth. The bacteria produce a potent toxin when infected by a specific bacteriophage that carries the toxin-encoding gene. This diphtheria toxin is responsible for the symptoms associated with diphtheria, such as sore throat, fever, and swollen glands, and can lead to more severe complications like myocarditis or neuropathy if left untreated.

Pathogenesis

The pathogenicity of Corynebacterium diphtheriae is largely attributed to its ability to produce the diphtheria toxin. This toxin inhibits protein synthesis in the host cells by inactivating elongation factor-2 (EF-2), leading to cell death. The severity of the disease is directly proportional to the amount of toxin produced. Transmission of diphtheria occurs through respiratory droplets from coughs or sneezes of an infected person or carrier. Upon entering the host, the bacteria adhere to the epithelial cells of the upper respiratory tract, where they begin to produce the toxin.

Clinical Manifestations

Diphtheria is characterized by the formation of a thick, gray pseudomembrane on the tonsils, pharynx, or nasal cavity, difficulty breathing, and a sore throat. Without timely treatment, the toxin can spread through the bloodstream to other organs, leading to potentially fatal complications. Vaccination has significantly reduced the incidence of diphtheria worldwide.

Prevention and Treatment

The primary method of prevention is vaccination with the diphtheria toxoid, which is often combined with tetanus and pertussis vaccines (DTP). Treatment of diphtheria involves the administration of diphtheria antitoxin to neutralize the toxin, along with antibiotics such as penicillin or erythromycin to eradicate the bacterial infection.

Epidemiology

The introduction of widespread vaccination campaigns has dramatically decreased the incidence of diphtheria in many parts of the world. However, outbreaks can still occur, particularly in areas where vaccination coverage is incomplete or in populations with decreased vaccine-induced immunity.

History

Diphtheria was a major cause of illness and death in children until the late 19th and early 20th centuries when the diphtheria toxin was discovered, and effective treatment and vaccination strategies were developed. The bacterium was first described by Edwin Klebs in 1883, and Friedrich Loeffler subsequently identified the organism as the causative agent of diphtheria in 1884.