First Report of Ocellatin-VT from the Skin Secretion of Leptodactylus vastus Lutz (Amphibia: Leptodactylidae)

The global emergency of antimicrobial resistance has drawn several efforts to evaluate new drug candidates, such as natural defensive biomolecules. Ocellatins are a group of antimicrobial peptides found in anurans of the Leptodactylidae family. This work investigated the presence of antimicrobial peptides in the skin secretion of Leptodactylus vastus from the Brazilian northeast. The secretion was fractionated by RP-HPLC, and the fractions were screened for antibacterial activity. A peptide isolated from the most active fraction was characterized for primary structure and evaluated for antibacterial activity, cytotoxicity to murine melanoma cells (B16-F10), and hemolytic activity. The RP-HPLC profile displayed 26 fractions, with fraction 25 being the most active. One of the two peptides present in this fraction had the primary structure determined, belonging to the group of ocellatins. Since it was not identical to other ocellatins previously reported, it was named ocellatin-VT. This peptide especially inhibited Gram-negative bacteria growth, with the highest activity against Acinetobacter baumannii and Escherichia coli (growth inhibition was higher than 95% at 8 and 16 µM, respectively). Ocellatin-VT was weakly cytotoxic to B16-F10 cells and showed low hemolytic activity. In conclusion, a new ocellatin was isolated from L. vastus skin secretion that was active against non-resistant and multidrug-resistant bacteria.