Gramicidin

Gramicidin is a heterogeneous mixture of three antibiotic compounds, gramicidins A, B and C, making up 80%, 6%, and 14%, respectively, all of which are obtained from the soil bacterial species Bacillus brevis and called collectively gramicidin D. Gramicidin D contains linear pentadecapeptides, that is chains made up of 15 amino acids. This is in contrast to gramicidin S, which is a cyclic peptide chain.