From the Super Mario Wiki
Louis Pasteur was a French scientist who pioneered research and techniques that paved the way for modern immunology and vaccinations. He, alongside his assistants (notably Pierre Paul Emile Roux), managed to create a rabies vaccine. Alongside his work with vaccines, he also devised a method of heating milk and wine in a way that eliminated dangerous microorganisms without harming the taste, a process that was dubbed "pasteurization" in honor of him, as well as analysed silkworms to see how they were destroying silk products.
Mario's Time Machine
According to Mario's Time Machine, before Louis Pasteur could finalize the rabies vaccine in 1885 in Paris, Bowser steals a Flask containing part of the vaccine after traveling back in time, and Mario later meets him to return the Flask after traveling back in time himself. However, Mario first talks to various people within Paris, as he does not know that the Flask belongs to Louis. If Mario attempts to visit him beforehand, Louis tells him to leave, as he needs to use the rabies vaccine on a diseased boy, but he is unable to find it. All of them talk at length about the backstory and experiments of Louis, including a waiter who was a student in Louis' classes and Pierre Paul Emile Roux. Eventually, Pierre tells him to return the Flask to Louis, and after definitely confirming it, Mario visits him in his lab and gives it to him. Louis excitedly tells Mario that he can now complete the vaccine and save the boy's life, and profusely thanks Mario. Louis assures Mario that the boy is going to be fine, and proclaims that the names of Pasteur and Mario are going to be famous.