Plague is primarily caused by which bacterium?

Plague is primarily caused by the bacterium Yersinia pestis, which is well known for being the pathogen responsible for historical pandemics, including the Black Death in the 14th century. Yersinia pestis is primarily transmitted to humans through the bites of infected fleas that live on rodents, though it can also be transmitted through direct contact with infected animals or inhalation of respiratory droplets from infected individuals.

Understanding the nature of each of the other bacteria can help clarify why Yersinia pestis is distinctly associated with plague. Escherichia coli is commonly found in the intestines of humans and animals and is often associated with foodborne illnesses and urinary tract infections, but not plague. Mycobacterium tuberculosis is the causative agent of tuberculosis, a serious respiratory disease, while Bartonella henselae is responsible for cat scratch fever, a condition stemming from a bacterial infection usually passed through scratches or bites from cats. None of these organisms are related to the transmission or pathology associated with plague, making Yersinia pestis the correct and relevant answer in this context.