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Louis Pasteur, a French chemist and microbiologist, was one of the most important founders of medical microbiology. He was born on 27th December in 1822, in France. Pasteur's contributions to science , technology and medicine are nearly without precedent. He poineered the study of molecular asymmetry; discovered that microorganism cause fermentation and disease; originated the process of pasteurisation: saved the beer, wine and silk industries in France; and developed vaccines against anthrax and rabies.

Pasteur's academic positions were numerous, and his scientific accomplishments earned him France's highest decoration, the Legion of Honour, as well as election to the Academie des Sciences and many other distinctions. The theoretical implications and practical importance of Pasteur's work were immense. Pasteur once said,  "There are no such things as pure and applied science; there are only science and the application of science. "Thus, once he established the theoretical basis of a given process, he investigated ways to further develop industrial applications. However, Pasteur did not have enough time to explore all the practical aspects of his numerous theories. One of the most important theoretical implications of his later research, which emerged form his attenuation procedure for vaccines, is the concept that virulence is not a constant attribute but a variable property - a property that can be lost and later recovered.