Which scientist first observed bacteria using a microscope?

Antonie van Leeuwenhoek was the first scientist to observe bacteria using a microscope. In the 1670s, the Dutch lensmaker examined water, dental material, and other samples with small, powerful single-lens microscopes that he designed and built himself.

In a 1676 letter to the Royal Society of London, Leeuwenhoek described tiny living organisms in water and called them “animalcules.” His observations included both bacteria and other microorganisms, which he did not yet classify as separate biological groups. He was also among the first people to observe protozoa, sperm cells, red blood cells, muscle fibers, and blood moving through capillaries.

Robert Hooke was an important earlier microscopist: his 1665 book Micrographia included famous drawings of cork and other structures. However, Hooke did not make the first accepted observations of bacteria. Robert Koch and Louis Pasteur came much later and established major advances in bacterial isolation, disease research, and germ theory.

Leeuwenhoek’s work earned him the title “Father of Microbiology,” although modern microbiology developed through the contributions of many later researchers.