Which German scientist identified the diphtheria bacillus in 1884?

Which German scientist identified the diphtheria bacillus in 1884? Friedrich Loeffler did.

Working with Robert Koch’s laboratory and building on Edwin Klebs’s earlier observation, Loeffler investigated the microorganism associated with diphtheria. In 1884, he described the organism now called Corynebacterium diphtheriae, showed where it occurred in infected patients, cultivated it, and reproduced diphtheria-like disease in susceptible animals.

The wording matters because Klebs identified the bacillus microscopically in 1883, whereas Loeffler’s 1884 work provided a fuller bacteriological demonstration. For that reason, the organism was historically called the Klebs–Loeffler bacillus. Loeffler also proposed that the bacterium produced a poisonous substance, an insight later confirmed when Emil Roux and Alexandre Yersin demonstrated diphtheria toxin in 1888.

A common mix-up is attributing the entire discovery to Robert Koch, who was Loeffler’s influential colleague and mentor. Loeffler’s research helped establish the bacterial cause of diphtheria and ultimately supported the development of antitoxin therapy.