The present invention provides an isolated polypeptide (escapin), and fragments thereof, from the sea hare Aplysia californica that have antimicrobial action directed against fungi, yeast, bacteria, and cyanobacteria. Further, the present invention provides an isolated nucleic acid, and fragments thereof, that encode the polypeptide and fragments thereof. Also provided are primers for detecting the nucleic acids of the present invention. A method of inhibiting microbial growth and inhibiting biofilm formation on a surface is also provided.