Hint: (a)He was a French biologist, microbiologist, and chemist. Today, he is often regarded as one of the fathers of germ theory.
(b)He was a French biologist, microbiologist, and chemist. He is also known for the discovery of fermentation.
(c)He was a Scottish physician and microbiologist. He is also known for the discoveries of the enzyme lysozyme.
(d)He was an English physician and scientist. He is often called "the father of immunology", and his work is claimed to have "saved more lives than the work of the other human".
(a)Louis Pasteur discovered the process of fermentation within the Yeast cells in 1857. Fermentation is the procedure of the transformation of sugar into alcohol. Yeasts convert sugar into alcohol during fermentation.
(b)Louis Pasteur proposed the Germ Theory of Disease in 1860-64. The germ theory of disease is currently the accepted scientific theory for several diseases. It states that microorganisms referred to as pathogens or "germs" can cause disease. These small organisms, too small to visualize without magnification, invade humans, other animals, and other living hosts. Their growth and reproduction inside an individual’s hosts can cause disease.
(c)Alexander Fleming discovered penicillin in 1928. This discovery led the way to the introduction of antibiotics that significantly reduced the number of deaths from infection.
(d)Edward Jenner developed a smallpox vaccine in 1796. He was the first successful vaccine to be developed. He observed that milkmaids who previously had caught cowpox didn't catch smallpox and showed that inoculated vaccines protected against the inoculated smallpox virus.
Note: "Germ" may ask not just a bacterium but to any sort of microorganism or maybe non-living pathogens which will cause disease, like protists, fungi, viruses, prions, or viroids. In the final decades of the 19th century, Koch conclusively established that a selected germ could cause a specific disease.