bac·i·tra·cin 
(b
ăs
′ĭ-tr
ās
ĭn)
n. A polypeptide antibiotic obtained from a strain of a bacterium (Bacillus subtilis) and used as a topical ointment in the treatment of certain bacterial infections, especially those caused by cocci.
[BACI(LLUS) + Trac(y I), laboratory designation of the strain of bacterium producing it (apparently from misspelling of the name of Margaret Treacy (1936?-1994), American child from whose tissue the strain was first isolated) + -IN.]