Yersinia pestis is a bacterium in the family Enterobacteriaceae; it is the infectious agent of bubonic plague. It was discovered simultaneously by Shibasaburo Kitasato and Alexandre Yersin in 1894.
The bacillus was originally called Pasteurella pestis, and was renamed after Alexandre Yersin.
Yersinia pestis is related to Yersinia pseudotuberculosis and Yersinia enterocolitica.