Which bacterium caused the Black Death pandemic of the 14th century?

Yersinia pestis caused the Black Death pandemic of the 14th century.

The pandemic reached Europe in 1347 and spread widely during the following years, killing tens of millions of people across Europe, Asia and North Africa. Yersinia pestis is a bacterium that can circulate among rodents and be transmitted by infected fleas. It can cause bubonic plague, in which swollen lymph nodes called buboes are characteristic, as well as septicemic and pneumonic forms.

The Black Death was not a single brief outbreak but part of the second plague pandemic, which continued in recurring waves for centuries. One well-known early outbreak occurred at Caffa in Crimea, and trade routes helped carry the disease across regions. Modern genetic research has identified Yersinia pestis DNA in medieval victims, supporting historical and archaeological evidence.

Plague still exists in some parts of the world, but antibiotics can treat it when diagnosis and treatment occur promptly. The disease is not the same as cholera or tuberculosis, which are caused by different bacteria and spread through different principal routes.