Diphtheria

University of Oklahoma Study Abroad Microbiology in Arezzo, Italy[1]

Etiology/Bacteriology

Taxonomy

Description

Corynebacterium diphtheriae is a gram-positive, non-motile, aerobic, and rod-shaped bacterium that causes diphtheria. There are four main subspecies that have been recognized: C. diphtheriae mitis, C. diphtheriae intermedius, C. diphtheriae gravis, and C. diphtheriae belfanti. C. diphtheriae gravis has the fastest generation time out of the four, allowing it to impose its toxic effects sooner. They can all be characterized as toxigenic or non-toxigenic, or those causing diphtheria and those that don’t, respectively. Diphtheria is an upper respiratory tract infection initially resulting in a sore throat and mild fever, but can progress to other more serious symptoms if not treated [1]. It can also infect the skin when lesions are exposed to the bacteria. Even though there are thousands of reported cases each year, the threat of contracting or succumbing to this illness has dramatically decreased due to advancements in antibiotic treatment and development of vaccinations [2].

Pili

The pili found on the surface of C. diphtheriae are beneficial in the adherence to host cells. There are three distinct types of pili expressed including SpaA-, SpaD-, and SpaH- (Spa for sortase-mediated pilus assembly). They are all structurally similar, but have different functions. SpaA- specifically allows for the adherence to pharyngeal epithelial cells, while SpaD- and SpaH- display specificity for binding to lung and laryngeal epithelial cells. There are also two minor pili, SpaB and SpaC proteins, that only bind to pharyngeal cells. The presence of these various pili on C. diphtheriae help it to adhere to certain surfaces, which is necessary for colonization of the host [3].