Why was the invention of the microscope important to microbiology?

The invention of the microscope was the foundational event that launched microbiology as a scientific discipline. Before its development, the existence of a vast, complex world of microorganisms remained entirely unknown to science.123

The importance of the microscope to the field includes:

• Direct Observation: It allowed early pioneers like Antonie van Leeuwenhoek to provide the first documented observations of bacteria and protozoa, which he famously termed "animalcules".14
• Refutation of Spontaneous Generation: By enabling the study of the life cycles of lower organisms, the microscope helped scientists disprove the doctrine of spontaneous generation, demonstrating that these creatures reproduced through regular biological processes.4
• Foundation for Modern Theory: The instrument was essential for the development of cell theory and the germ theory of disease, which identified microorganisms as the specific causes of many human illnesses.5
• Technological Evolution: Subsequent improvements in lens quality and the later invention of the electron microscope vastly increased resolving power, allowing researchers to study cellular structures, viruses, and molecular-level interactions.26