An isolated peptide including an amino acid sequence of formula (II): ##STR00001## wherein Xaa is Ser-Phe-Gly-Leu, Xab is Arg-Leu-Arg-Arg-Gly-Phe, Xac is Ala-Xac2-Gly-Arg, Xad is Arg-Phe-Pro-Ser-Ile-Pro-Ile-Gly-Arg, Xae is Ser-Arg-Phe-Val-Gln, and Xaf is Arg-Arg-Val-Trp, Xac2 is histidine or arginine, Ca1, Ca2, Ca3, Ca4, Ca5 and Ca6 are sulfur containing amino acids, wherein each of Ca1-Ca5, Ca2-Ca4 and Ca3-Ca6 are linked together by a sulfur bridge, and wherein the amino acid sequence has antimicrobial activity.