pol·y·myx·in 
(pŏl′ē-mĭksĭn)
(pŏl′ē-mĭksĭn)n.
Any of various mainly toxic antibiotics derived from strains of the soil bacterium Bacillus polymyxa and used to treat various infections with gram-negative bacteria.
[New Latin polymyxa, specific epithet (POLY- + Greek muxa, slime) + -IN.]