How did Antonie van Leeuwenhoek’s microscope observations help begin microbiology?

Antonie van Leeuwenhoek is credited with effectively beginning the discipline of microbiology through his pioneering use of high-quality, single-lens microscopes in the 1670s.12

By hand-grinding lenses capable of high magnification, Leeuwenhoek was the first to observe and describe bacteria and protozoa, which he famously termed "animalcules". His meticulous observations of these microorganisms—found in sources ranging from rainwater to the human mouth—provided the first empirical evidence of a microscopic world previously unknown to science.13

Furthermore, Leeuwenhoek’s studies of the life cycles of various lower animals, such as fleas, ants, and weevils, provided critical evidence that refuted the long-held doctrine of spontaneous generation. By demonstrating that these organisms reproduced through regular biological processes rather than emerging from nonliving matter, he laid the foundational groundwork for bacteriology and protozoology, ultimately challenging the scientific paradigms of his time.413