Streptomycin is an antibiotic. At the time it was developed, it was as great a breakthrough as penicillin had been because it killed a wider range of bacteria than did it's predecessor. It was the first antibiotic that was effective against tuberculosis. It is also effective against plague.
Streptomycin was first isolated in 1943. Ironically, the chemical was isolated from a type of bacteria. It was given its first clinical trials from 1946-1947. These clinical trials were the first to be carried out under modern double-blind procedures with a control group and showed that the drug was effective against tuberculosis, although it did have some toxicity. It also showed the start of bacterial antibiotic resistance.
Streptomycin works by preventing the bacteria from synthesizing proteins. It does not have the same effect on the ability of humans to create proteins, and therefore is not generally toxic at therapeutic doses. It also means streptomycin will work against bacteria that don't have a cell wall and is appropriate as a broad-spectrum antibiotic when the exact infection is not known.