In 3500 BC the Sumerian doctors would give patients beer soup mixed with snakeskins and turtle shells.
Babylonian doctors would heal the eyes by using an ointment made of frog bile and sour milk.
The Greeks used many herbs to heal ailments.
All of these "natural" treatments contained some sort of antibiotic.
Louis Pasteur was one of the first recognized physicians who observed that bacteria could be used to kill other bacteria.
In 1929 Sir Alexander Fleming, a Scottish bacteriologist, went on a vaction and left a petri dish of staphylococci bacteria uncovered. When he returned, he noticed that there was mold growing on it. Upon further examination, he saw that the area around the mold had no bacteria growing. He named the mold Penicillium, and the chemical produced by the mold was named penicillin, which is the first substance recognized as an antibiotic.
Almost immediately after penicillin was introduced, resistance in certain strains of staphylococci was noticed.
In 1935, Domagk discovers synthetic antimicrobial chemicals (sulfonamides).
During World War II, because of need for antibiotic agents, penicillin was isolated and further tested by injection into animals. It was found to be extremely useful in curing infections, and to have extremely low toxicity to the animals. Because of these findings, use of penicillin greatly increased. This also spurred a search of other chemical agents of similar use.
In the late 1940's through the early 1950's, streptomycin, chloramphenicol, and tetracycline were discovered and introduced as antibiotics.
In 1953, during a Shigella outbreak in Japan, a certain strain of dysentery bacillus was found to be resistant to chloramphenicol, tetracycline, streptomycin, and the sulfanilamides.
By the 1950's it was apparant that tuberculosis bacteria was rapidly developing resistance to streptomycin, which had commonly been used to treat it.