Antibiotic resistance is at dangerous levels and increasing worldwide. The search for new antimicrobial drugs to counteract this problem is a priority for health institutions and organizations, both globally and in individual countries. Sarconesiopsis magellanica blowfly larval excretions and secretions (ES) are an important source for isolating antimicrobial peptides (AMPs). This study aims to identify and characterize a new S. magellanica AMP. RP-HPLC was used to fractionate ES, using C18 columns, and their antimicrobial activity was evaluated. The peptide sequence of the fraction collected at 43.7 min was determined by mass spectrometry (MS). Fluorescence and electronic microscopy were used to evaluate the mechanism of action. Toxicity was tested on HeLa cells and human erythrocytes; physicochemical properties were evaluated. The molecule in the ES was characterized as sarconesin II and it showed activity against Gram-negative (Escherichia coli MG1655, Pseudomonas aeruginosa ATCC 27853, P. aeruginosa PA14) and Gram-positive (Staphylococcus aureus ATCC 29213, Micrococcus luteus A270) bacteria. The lowest minimum inhibitory concentration obtained was 1.9 μM for M. luteus A270; the AMP had no toxicity in any cells tested here and its action in bacterial membrane and DNA was confirmed. Sarconesin II was documented as a conserved domain of the ATP synthase protein belonging to the Fli-1 superfamily. The data reported here indicated that peptides could be alternative therapeutic candidates for use in infections against Gram-negative and Gram-positive bacteria and eventually as a new resource of compounds for combating multidrug-resistant bacteria.

We evaluated extracts taken fromS. magellanicathird instar larvae fat body and haemolymph using a diabetic rabbit model and compared this to the effect obtained with the same substances taken fromLucilia sericatalarvae. Alloxan (a toxic glucose analogue) was used to induce experimental diabetes in twelve rabbits. Dorsal wounds were made in each animal and they were infected withStaphylococcus aureusandPseudomonas aeruginosa. They were then treated with haemolymph and lyophilized extracts taken from the selected blowflies’ larvae fat bodies. Each wound was then evaluated by using rating scales and histological analysis. More favourable scores were recorded on the PUSH and WBS scales for the wounds treated with fat body derived from the larvae of both species compared to that obtained with haemolymph; however, wounds treated with the substances taken fromS. magellanicahad better evolution. Histological analysis revealed that treatment led to tissue proliferation and more effective neovascularisation in less time with both species’ fat body extracts compared to treatment with just haemolymph. The results suggest the effectiveness of the substances evaluated and validate them in the animal model being used here as topical agents in treating chronic wounds.

ResumenObjetivoEvaluar, 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 métodosSe 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).ResultadosDespués 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.ConclusionesLos resultados obtenidos sugieren que estas sustancias podrían tener un efecto similar en el tratamiento de heridas infectadas contra los microorganismos evaluados.AbstractObjectiveThis 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 methodsFat 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).ResultsHemolymph 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.ConclusionsThe 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