BACKGROUND The inappropriate use of antibiotics has led to the accelerated growth of resistance to antibiotics. The search for new therapeutic strategies (i.e., antimicrobial peptides-AMPs) has thus become a pressing need. OBJECTIVE Characterising and evaluating Sarconesiopsis magellanica larval fat body-derived AMPs. METHODS Fat body extracts were analysed by reversed-phase high-performance liquid chromatography (RP-HPLC); mass spectrometry was used for characterising the primary structure of the AMPs so found. ProtParam (Expasy) was used for analysing the AMPs’ physico-chemical properties. Synthetic AMPs’ antibacterial activity was evaluated. FINDINGS Four new AMPs were obtained and called sarconesin III, IV, V and VI. Sarconesin III had an α-helix structure and sarconesins IV, V and VI had linear formations. Oligomer prediction highlighted peptide-peptide interactions, suggesting that sarconesins III, V and VI could form self-aggregations when in contact with the microbial membrane. AMPs synthesised from their native molecules’ sequences had potent activity against Gram-positive bacteria and, to a lesser extent, against Gram-negative and drug-resistant bacteria. Sarconesin VI was the most efficient AMP. None of the four synthetic AMPs had a cytotoxic effect. MAIN CONCLUSIONS S. magellanica larval fat body-derived antimicrobial peptides are an important source of AMPs and could be used in different antimicrobial therapies and overcoming bacterial resistance.

Objetivo: Evaluar, en condiciones in vitro , la actividad antibacterial de los extractos de cuerpos grasos y de la hemolinfa de larvas de tercer estadio de Sarconesiopsis magellanica , la cual se comparó con los efectos obtenidos de las mismas sustancias derivadas de Lucilia sericata . S. magellanica (Diptera: Calliphoridae) es una mosca de importancia principalmente forense, utilizada en la determinación del intervalo post mortem . Por sus hábitos necrófagos, es considerada un modelo potencialmente útil en terapia larval. Material y métodos: Se extrajeron los cuerpos grasos de las larvas mediante la técnica de disección corporal y la hemolinfa se obtuvo mediante decapitación y centrifugación de los especímenes larvales. Las bacterias evaluadas fueron Staphylococcus aureus y Pseudomonas aeruginosa . Los métodos utilizados para evaluar la actividad antibacterial fueron difusión en agar y unidades formadoras de colonias (UFC/ml). Resultados: Después de la correspondiente incubación, los resultados generales mostraron que la actividad antibacterial de la hemolinfa y de los cuerpos grasos, tanto de L. sericata como de S. magellanica , fueron efectivos contra S. aureus y P. aeruginosa sin diferencias significativas entre las especies de moscas, aunque con algunas diferencias entre las cepas bacterianas. Conclusiones: Los resultados obtenidos sugieren que estas sustancias podrían tener un efecto similar en el tratamiento de heridas infectadas contra los microorganismos evaluados.

Objective: This study aimed to evaluate the in vitro antibacterial activity of fat body and hemolymph extracts from Sarconesiopsis magellanica (Diptera: Calliphoridae) third-instar larvae, compared to the effect obtained using the same extracts but derived from Lucilia sericata . S. magellanica blowflies are considered important in forensic sciences due to their usefulness in determining the post mortem interval. This blowfly could be useful in larval therapy due to its necrophagous habits. Materials and methods: Fat body from larvae was removed by dissection, and hemolymph via decapitation and centrifugation of larval specimens. The antibacterial effect was tested against Staphylococcus aureus and Pseudomonas aeruginosa using two methods: agar diffusion and colony forming units (CFU/mL). Results: Hemolymph and fat body extracts derived from both L. sericata and S. magellanica were effective against S. aureus and P. aeruginosa , with no significant differences between blowfly species, although with some differences between the bacterial strains. Conclusions: The results obtained suggest that S. magellanica and L. sericata fat body and hemolymph extracts might have a similar antimicrobial activity against these microorganisms when used to treat infected wounds.