Final answer:
The bacterial pathogen causing plague is Yersinia pestis, responsible for historic pandemics and current cases treatable with antibiotics.
Step-by-step explanation:
The bacterial pathogen that causes plague is Yersinia pestis. This gram-negative bacillus is known for causing the zoonotic infection known as the plague, which includes forms such as bubonic plague, pneumonic plague, and septicemic plague. Historically significant, Y. pestis caused pandemics with high mortality rates, most notably the pandemic in the 14th century. In modern times, there are about 1,000 to 3,000 cases of these types of plagues each year, primarily bubonic and pneumonic, which are now effectively treated with antibiotics.