n. (1940) [ Bacillus + Margaret Tracy, (a child whose tissues contained Bacillus subtilis) + -in. RHUD. ] a polypeptide antibacterial antibiotic of known chemical structure effective against several types of Gram-positive organisms, and usually used topically for superficial local infection. It is produced by Bacillus subtilis and Bacillus licheniformis, and as produced commercially is composed of several closely related substances. The predominant component, Bacitracin A, has a formula C60H103N17O16S, and contains D-ornithine, D-phenylalanine and D-glutamine residues as well as the L-isomers of leucine, isoleucine, histidine, asparagine and aspartic acid. [ MI11 ] [ WordNet 1.5 ]