Yersinia pestis is infamous for causing the devastating disease plague that has been affecting people for at least 5,000 years. Yersinia pestis is a type of disease-causing bacteria that causes all three forms of plague; bubonic, septicemic, and pneumonic.
Bubonic plague is widely known as the disease behind the devastating "Black Death" of the European Middle Ages that killed up to 60 percent of the European population, according to CDC. The name of the bacteria comes from doctor and bacteriologist Alexandre Yersin, who discovered that Y. pestis causes plague in the mid-1890s while studying a plague epidemic in Hong Kong. When a flea feeds on an infected rodent, such as a rat, it swallows Y. pestis. The bacteria then populates in the gut of the flea and produces an enzyme that clots the blood the flea ingests, preventing the blood from moving past the flea's esophagus. Fleas are incapable to fully ingest blood, so every time it tries to feed on an animal, it ends up regurgitating the blood thus newly infecting the host with Y. pestis.
I find it interesting that the mechanisms by which Y. pestis specifically cause primary pneumonic plague, a respiratory form of disease. It's also a very old disease and even though it's not a major concern in today's society, it always has the chance to evolve and impact us.