Dung beetles are exposed to a complex microbiological ecosystem during their life cycle. Characterization of novel host-defense peptides (HDP) is essential to understanding the host innate immune response in insects. It constitutes a promising alternative to look for new therapeutic agents against pathogenic microbes. We identified four new HDP, Oxysterlins 1, 2, 3, and 4 from the transcriptome of the Oxysternon conspicillatum dung beetle. These HDP display a highly conserved signal peptide and a mature peptide, characterized by an overall positive charge (cationic) (pI: 10.23–11.49), a hydrophobic ratio (ΦH: 35–41), and amphipathicity. Oxysterlins 1, 2, and 3 have a linear α-helix structure, whilst Oxysterlin 4 has a mixture of both α-helix and β-sheet structures without disulfide bonds through bioinformatics prediction and circular dichroism. Oxysterlins are part of the cecropin family group in an exclusive clade related to beetle cecropins. They have predominant antimicrobial activity against Gram-negative bacteria, including multidrug resistant strains (3.12–50 μg/mL) measured by plate microdilution. Their kinetics, in a time-killing curve showed concentration-dependent bactericidal activity. Furthermore, these HDP have low toxicity against human erythrocytes (62.5–500 μg/mL) and Vero cells (250–500 μg/mL). This article describes new HDP of the cecropin family from the Oxysternon conspicillatum dung beetle, with antimicrobial activity against multidrug resistant bacteria and low toxicity.

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Este método es basado en el método clásico de micro-dilución en placa de NCLSS (National Committee of Laboratory Safety and Standards (NCLSS) como fue publicado en Amsterdam, D. 1996. Susceptibility testing of Antimicrobials in liquid media. In 'Antibiotics in Laboratory Medicine', Lorian, V., ed. Fourth Edition, pp.52-111. Williams and Wilkins, Baltimore.Modificado con respecto a la lectura de la placa utilizando un indicador metabólico para incrementar la sensibilidad de la prueba respecto al crecimiento de las bacterias.La realizacion de este protocolo fue posible gracias al apoyo del departamento administrativo de ciencia tecnología e innovacion, Colciencias a traves del proyecto 111356933173 convocatoria569-2012.Este protocolo fue estandarizado con el desarrollo del proyecto de grado "OPTIMIZACIÓN DE UN MÉTODO PARA EVALUAR LA ACTIVIDAD ANTIBACTERIANA IN VITRO EN MICROVOLÚMENES" de la estudiante Juliana Franco para optar por el titulo de Biologa.

Este método es basado en el método clásico de micro-dilución en placa de NCLSS (National Committee of Laboratory Safety and Standards (NCLSS) como fue publicado en Amsterdam, D. 1996. Susceptibility testing of Antimicrobials in liquid media.In'Antibiotics in Laboratory Medicine', Lorian, V., ed. Fourth Edition, pp.52-111. Williams and Wilkins, Baltimore. Modificado conrespecto a la lectura de la placa utilizando unindicador metabólico para incrementar la sensibilidad de la prueba respecto al crecimiento de las bacterias.