This document summarizes the contributions of several scientists who were pioneers in microbiology: - Antonie van Leeuwenhoek was the first to observe microbes under a microscope and determine their small size. - Louis Pasteur established the germ theory of disease and developed pasteurization and microbial fermentation. - Edward Jenner pioneered the concept of vaccines by creating the smallpox vaccine, the world's first vaccine. - Robert Koch identified the specific causative agents of tuberculosis, cholera, and anthrax and developed Koch's postulates to link microbes to diseases. - Ignaz Semmelweis demonstrated that hand washing reduced mortality, establishing the importance of hygiene in