What instrument made the discovery of bacteria?

The discovery of bacteria was made possible by the microscope, specifically the simple microscope designed by Antonie van Leeuwenhoek in the late 17th century. Leeuwenhoek was the first to observe and describe single-celled organisms, which he called "animalcules," using his handcrafted microscopes. His observations laid the foundation for microbiology and the understanding of microscopic life.