The present invention relates to a chimeric nucleotide sequence encoding peptides with antimicrobial activity, to be expressed on plants as bioreactors, plant cell or transformed plant material and E. coli, where plants and bacteria were used for scale-up production of antimicrobial peptide and that produces the peptide sequence derived from nucleotide sequence SEQ ID No. 1, SEQ ID No. 6 and SEQ ID No. 12. It includes a method for obtaining the amino acids sequence SEQ ID No. 9 derived from a chimeric nucleotide sequence which encodes to antimicrobial peptides, wherein said amino acids sequence is derived from the synthetic DNA sequence SEQ ID No. 1, obtained from a back-translation of the amino acid sequence of the peptide Ap-S of Argopecten purpuratus scallop.