Yersinia pestis

[pĕstĭs]
n.
  1. A bacterium that causes plague and is transmitted from rats to humans by the rat flea Xenopsylla cheopis.Pasteurella pestis
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.