Novel doublet molecules of cecropin A from Drosophila melanogaster were designed and constructed combining the regular (CEC_dir) with the inverted (CEC_ret) coding sequence of the standard CEC A1 gene resulting in the following configurations: CEC_dir-CEC_retand CEC_ret-CEC_dir. These two recombinant molecules were generated using a three-primer driven PCR reaction yielding composite single functional aminoacidic molecules with the coding sequences of CEC_dir linked in frame with the coding sequence of CEC_ret and vice versa. In order to obtain these constructions, a retropeptide DNA-coding sequence was chemically synthesized to match the expected polarity of the newly generated CEC_ret sequence. Both doublet antimicrobial peptides (drAMPs) were cloned in the T7 promoter driven expression plasmid pET27b+ and expressed in E. coli BL21 without any fusion protein. Only the former recombinant peptide was expressed and purified from cell extracts and its specific activity against two different bacteria showed to be higher than those displayed by their monomer parental counterparts.