Cationic elastin-like polypeptides (CELP) are thermally responsive polypeptides that undergo an inverse temperature phase transition, and the recombinant CELP fusion proteins may be purified by inverse transition cycling (ITC). To obtain high-purity antimicrobial peptide cecropin AD (CAD), CELP was placed at the N-terminus of CAD and the expression vector pET28a-CELP-CAD was constructed. The expression vector was then transformed into Escherichia coli BL21 (DE3) to express the recombinant protein. After three rounds of ITC, enterokinase digestion and another hot spin, 1.2 mg recombinant CAD was purified from 100 ml culture medium. The antimicrobial test indicated that the high-purity CAD had strong antimicrobial activity against E. coli and Staphylococcus aureus. (C) 2012 Published by Elsevier Inc.