Antonie van Leeuwenhoek was a Dutch microbiologist who is considered the father of microbiology. He was the first person to observe and describe bacteria under the microscope in the 17th century. At the time, he did not have a complete understanding of the nature of these microorganisms and did not know that they were responsible for many diseases.
Van Leeuwenhoek referred to these tiny organisms as "animalcules" or "little animals" because of their movement. Later on, the French scientist, Louis Pasteur, suggested the term "microbe" for bacteria and other microscopic organisms. The word "bacteria" is derived from the Greek word "bakterion," meaning "small rod."
It is not clear why van Leeuwenhoek chose the name "bacteria" to describe these microorganisms. It may be that he used the term because he observed that many of these microorganisms were rod-shaped under the microscope. Additionally, he may have used the term to distinguish bacteria from other microorganisms he observed, such as fungi and protozoa.