Noun | 1. | gramicidin - an antibiotic produced by a soil bacterium; used chiefly as an antiseptic in treating local infections produced by Gram-positive bacteria antibiotic, antibiotic drug - a chemical substance derivable from a mold or bacterium that can kill microorganisms and cure bacterial infections; "when antibiotics were first discovered they were called wonder drugs" antiseptic - a substance that destroys micro-organisms that carry disease without harming body tissues |