Amanda CM Saúde,1 Alicia S Ombredane,1 Osmar N Silva,1 João ARG Barbosa,1,2 Susana E Moreno,3 Ana Claudia Guerra Araujo,4 Rosana Falcão,4 Luciano P Silva,4 Simoni C Dias,1 Octávio L Franco1,3 1Programa de Pós Graduação em Ciências Genômicas e Biotecnologia, Centro de Análises Proteômicas e Bioquímicas, Universidade Católica de Brasília, Brasília, FD, Brazil; 2Laboratório de Biofísica-Departamento de Biologia Celular-IB, Universidade de Brasília – UNB, DF, Brazil; 3Universidade Católica Dom Bosco – UCDB, Campo Grande, MS, Brazil; 4Empresa Brasileira de Pesquisa Agropecuária – EMBRAPA – Recursos Genéticos e Biotecnologia, Brasília, DF, Brazil Abstract: Controlling human pathogenic bacteria is a worldwide problem due to increasing bacterial resistance. This has prompted a number of studies investigating peptides isolated from marine animals as a possible alternative for control of human pathogen infections. Clavanins are antimicrobial peptides isolated from the marine tunicate Styela clava, showing 23 amino acid residues in length, cationic properties, and also high bactericidal activity. In spite of clear benefits from the use of peptides, currently 95% of peptide properties have limited pharmaceutical applicability, such as low solubility and short half-life in the circulatory system. Here, nanobiotechnology was used to encapsulate clavanin A in order to develop nanoantibiotics against bacterial sepsis. Clavanin was nanostructured using EUDRAGIT® L 100-55 and RS 30 D solution (3:1 w:w). Atomic force, scanning electron microscopy and dynamic light scattering showed nanoparticles ranging from 120 to 372 nm in diameter, with a zeta potential of -7.16 mV and a polydispersity index of 0.123. Encapsulation rate of 98% was assessed by reversed-phase chromatography. In vitro bioassays showed that the nanostructured clavanin was partially able to control development of Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Furthermore, nanostructures did not show hemolytic activity. In vivo sepsis bioassays were performed using C57BL6 mice strain inoculated with a polymicrobial suspension. Assays led to 100% survival rate under sub-lethal sepsis assays and 40% under lethal sepsis assays in the presence of nanoformulated clavanin A until the seventh day of the experiment. Data here reported indicated that nanostructured clavanin A form shows improved antimicrobial activity and has the potential to be used to treat polymicrobial infections. Keywords: peptides, antimicrobial, nanoparticles, nanobiotechnology