The Collaborative International Dictionary of English v.0.48:

bacitracin \bacitracin\ 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.

   Note: 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]

WordNet (r) 3.0 (2006):

bacitracin
    n 1: a polypeptide antibiotic of known chemical structure
         effective against several types of Gram-positive organisms;
         usually applied locally