The invention relates to a molecule comprising at least the amino acid sequence K X K X1 X2 X K G X wherein X is any amino acid residue X1, and X2 is K or R and wherein said molecule have a length of from about 10 to about 100 amino acid residues or an analogue thereof The invention also relates to compositions comprising said molecule and use of the molecule and/or composition of the invention to combat microorganisms, such as bacteria, viruses, fungi, including yeast, and parasites.