antibiotic synthesized by the soil organism Streptomyces griseus. Streptomycin was discovered by American biochemists Selman Waksman (Waksman, Selman Abraham), Albert Schatz, and Elizabeth Bugie in 1943. The drug acts by interfering with the ability of a microorganism to synthesize certain vital proteins. It was the first antimicrobial agent developed after penicillin and the first antibiotic effective in treating tuberculosis. Because it was effective against a wide variety of diseases, streptomycin was used often, with the result that many initially sensitive microorganisms, including the bacterium that causes tuberculosis, became resistant to the antibiotic. It is used in combination with penicillin for treating infections of heart valves ( endocarditis) and with tetracyclines (tetracycline) in the treatment of plague, tularemia, and brucellosis.