neomycin, broad spectrum antibiotic effective against both gram positive and gram negative bacteria (see Gram's stain). It interferes with protein synthesis in sensitive bacterial cells such as species of Proteus and Staphylococcus. Neomycin is mainly used topically in the treatment of skin and mucous membrane infections, wounds, and burns. Although it is also used systemically, it is highly toxic. Neomycin was first isolated in 1949 by the American microbiologist Selman Waksman from a strain of the bacterial species Streptomyces fradiae.