Novel doublet molecules of cecropin A from Drosophila melanogaster were designed and constructed combining the regular (CECdir) with the inverted (CECret) coding sequence of the standard CEC A1 gene resulting in the following configurations: CECdir-CECret and CECret-CECdir. These two recombinant molecules were generated using a three-primer driven PCR reaction yielding composite single functional aminoacidic molecules with the coding sequences of CECdir linked in frame with the coding sequence of CECret 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 CECret 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.