Pasteur and the germ theory of disease
shown that microorganisms turned wine into vinegar,
by heating the wine you could kill the microorganisms that caused this,
he showed that if microorganisms were passed for one organism (in silkworms) to another then so was the disease.
Lister and the development of antiseptics and Flem
introduced carbolic acid disinfectant during operations to prevent infection, chemicals were also used to kill microorganisms on instruments and skin.
Noticed that a mould (penicillium) killed another bacteria
Later Floey and Chain succeeded in extracting the antibiotic penicillin from the mould