The diphtheria bacterium: illness comes from a toxin that only some strains produce. Explore its illustrative 3D model, human context, and sources.
CDC describes diphtheria as any illness caused by a toxin produced by some strains of C. diphtheriae, and toxin production depends on a bacteriophage carrying the tox gene. Respiratory diphtheria is the most serious form, where a thick grey pseudomembrane of dead tissue can build up in the nose and throat; skin infection is a separate presentation. People can carry the organism without becoming ill and still pass it on. Throat illness resembling diphtheria was described in antiquity, long before the bacterium was observed in 1883.
Disease potential depends on whether a strain carries the toxin gene, so carriage of C. diphtheriae is not automatically diphtheria. CDC reports that about 1 in 10 people with respiratory diphtheria die even with treatment, and up to half without it; WHO gives around 30% fatality for unvaccinated people without proper treatment. Vaccination status, treatment access and strain toxigenicity all matter.
Original schematic 3D phenotype. PHAC describes pleomorphic, aerobic, non-spore-forming, slightly club-shaped Gram-positive bacilli that occur as single cells, in pairs, in V forms, in palisades or in clusters, and are non-motile. No capsule, flagella or endospore is assigned. Colours, dimensions, layer thicknesses and displayed arrangements are diagram choices, not a measured individual cell. Independent scientific review remains pending.
Source check: 2026-09-19. Educational content; independent scientific review remains pending.