This invention concerns novel antibiotic peptide and peptide derivates, especially for use in medicine. Further, the invention relates to compositions and methods for killing microbes, like bacteria or fungus, and methods to treat microbial infections. The invention further relates to a method for drug screening analysis. The peptides and peptide derivates have the general formula Sub1-X1 N X2 X3 P V Y I P X4 X5 R P P H P-Sub2 (SEQ ID NO:169) wherein X1 is a neutral or positively charged moiety, X2 is a polar or positively charged moiety, X3 is a positively charged moiety, X4 is a polar or positively charged moiety, X5 is a proline or a proline derivate, Sub1 being the free or modified N-terminus, and Sub2 being the free or modified C-terminus. The peptides or peptide derivates according to the invention possess at least one of the following advantages compared to the natural occurring apidaecin peptides: (i) an increased half-live in mammalian serum due to a higher protease resistance and (ii) an increased antimicrobial activity against one or several bacterial strains, especially human pathogens, or fungus or other microbial infections (iii) show an enlarged spectrum of antimicrobial activity, (iv) do induce less resistance in microbes and (v) are not toxic to human cells including erythrocytes.
