Defensins are polypeptides which possess potent antibacterial activity against a broad range of bacteria. The human genome encodes ten α-defensin genes. The polypeptides contain 28 to 42 amino acids, including six conserved cysteine residues involved in intrachain disulfide bonds. Another characteristic is a high density of cationic charge, creating an amphiphilic molecule. The mechanism for killing microbes involves initial electrostatic interactions of the cationic groups with negatively charged phospholipids in the microbial membrane, followed by disruption of the bacterial membrane and cell death.