Tyrothricin is a large cyclic polypeptide antibiotic isolated from Brevibacillus brevis in 1939. The name Tyrothricin is derived from Tyrothrix, a name first used by Duclaux to designate sporulating aerobic bacteria. Tyrothricin is composed of a mixture of tyrocidine and gramicidin, which are short polypeptides with antimicrobial activity. The complex is a mixture comprised of 60% Tyrocidine and 40% gramicidins. Tyrocidine is composed of non-ribosomally produced cationic cyclic decapeptides (the six predominant tyrocidines are TrcA/A1, TrcB/B1, TrcC/C1) and adopts a β-sheet structure with both L and D amino acids. Gramicidins adopt similar B-sheet structures, and are neutral linear, with valine-Gramicidin A often the major component. Tyrothricin is soluble in alcohol and insoluble in water.