Gramicidin S (Gramicidin soviet) is a cationic cyclic peptide antibiotic. Gramicidin S is active against Gram-negative and Gram-positive bacteria by perturbing integrity of the bacterial membranes. Gramicidin S also inhibits cytochrome bd quinol oxidase.
References:
[1]. Mogi T, et al. Gramicidin S and polymyxins: the revival of cationic cyclic peptide antibiotics. Cell Mol Life Sci. 2009 Dec;66(23):3821-6.