The present invention provides novel therapeutic antimicrobial peptides that are bactericides and have an inhibitory effect on biofilms produced by biofilm-forming bacteria and especially biofilm-forming staphyloccocal bacteria. The invention includes the nucleic acids encoding the polypeptides, methods of treating bacterial infections, medical devices or implants or prosthetics impregnated with, covered or coated in the polypeptides, and means of delivery of the peptide to the oral cavity.