Yersinia pestis

Yersinia pestis is a bacillus (a type of bacteria). It is the bacterium that causes bubonic plague, septicemic plague, and pneumonic plague.

These three forms of the plague have killed many people in epidemics throughout history. Historians and scientists believe they caused the Black Death. This pandemic killed one out of every three people in Europe between 1347 and 1353. 

 Discovery 
In 1894 a physician named Alexandre Yersin discovered the Y. pestis bacillus during an epidemic of the plague in Hong Kong. Yersin worked for the Pasteur Institute at the time.

The bacillus's name was changed several times:

 1894-1900: Bacterium pestis 
 1900-1923: Bacillus pestis
 1923-1970: Pasteurella pestis (named to honor Louis Pasteur)

Before 1970, scientists thought the bacillus belonged to the Pasteurella genus of bacteria. In 1970 they reclassified it as its own genus (Yersinia) and named it Yersinia pestis in Alexandre Yersin's honor.

Scientists have found three varieties of Y. pestis.

 The Black Death 
See the main article: The Black Death

Historians do not agree about Y. pestis's role in the Black Death. Many believe that Y. pestis was the bacterium that caused the Black Death. However, others say the Black Death spread much faster than Y. pestis could. 

Still, DNA from Y. pestis has been found in the teeth of some exhumed Black Death victims. For this reason, Y. pestis must have played a role in the epidemic, and it probably did too in other European plague epidemics.
 References 

 Other websites 

 Yersinia pestis . Virtual Museum of Bacteria.
 Genome information is available from the NIAID PathoSystems Resource Integration Center (PATRIC) 

Category:Gram-negative bacteria
Category:Plague