Learned that microbes are living and caused disease. Also learned that killing the microbes helped to stop that disease.

Robert Koch identified specific bacteria causing diseases such as tuberculosis and anthrax, but he is not primarily credited with the broader principle that killing microbes stops disease spread.

Edward Jenner pioneered vaccination against smallpox in 1796 but did not establish germ theory or the general concept that destroying microbes halts disease.

Louis Pasteur developed the germ theory of disease, proving that living microorganisms cause illness. His pasteurization experiments demonstrated that applying heat to kill microbes prevents spoilage and disease, directly linking microbial destruction to disease prevention.