– Gramicidin (Gramicidine) is an antimicrobial peptide. Gramicidin dimers form ion channel-like pores in the cell membranes and organelles of bacterial and animal cells, allowing inorganic monovalent ions, such as potassium and sodium ions, to pass freely through the pores by diffusion, disrupting the important ionic gradient between membranes and thus killing the cells by various actions. Gramicidin is effective against Gram-positive bacteria such as Bacillus subtilis and Staphylococcus aureus, but is not as effective against Gram-negative bacteria such as Escherichia coli.