Bicarinalin

Acinetobacter baumannii has been identified by the WHO as a high priority pathogen. It can be resistant to multiple antibiotics and colistin sulphate is often used as a last-resort treatment. However, the potentially severe side-effects of colistin are well documented and this study compared the bactericidal and anti-biofilm activity of two synthetic nature-inspired antimicrobial peptides, bicarinalin and BP100, with colistin. The minimum bactericidal concentration (MBC) against planktonic A. baumannii was approximately 0.5 μg/ml for colistin sulphate and ~4 μg/ml for bicarinalin and BP100. A. baumannii commonly occurs as a biofilm and biofilm removal assay results highlighted that both bicarinalin and BP100 had significantly greater potential than colistin. Atomic force microscopy (AFM) showed dramatic changes in A. baumannii cell size and surface conformity when treated with peptide concentrations at and above the MBC. Scanning electron microscopy (SEM) visualised the reduction of biofilm coverage and cell surface changes as peptide concentration increased. Liposome assays revealed that these peptides most likely act as pore-forming agents in the membrane. Bicarinalin and BP100 may be effective therapeutic alternatives to colistin against A. baumannii infections but further research is required to assess if they elicit cytotoxicity issues in patients.

The venom peptide bicarinalin, previously isolated from the ant Tetramorium bicarinatum, is an antimicrobial agent with a broad spectrum of activity. In this study, we investigate the potential of bicarinalin as a novel agent against Helicobacter pylori, which causes several gastric diseases. First, the effects of synthetic bicarinalin have been tested against Helicobacter pylori: one ATCC strain, and forty-four isolated from stomach ulcer biopsies of Peruvian patients. Then the cytoxicity of bicarinalin on human gastric cells and murine peritoneal macrophages was measured using XTT and MTT assays, respectively. Finally, the preventive effect of bicarinalin was evaluated by scanning electron microscopy using an adherence assay of H. pylori on human gastric cells treated with bicarinalin. This peptide has a potent antibacterial activity at the same magnitude as four antibiotics currently used in therapies against H. pylori. Bicarinalin also inhibited adherence of H. pylori to gastric cells with an IC50 of 0.12 μg·mL-1 and had low toxicity for human cells. Scanning electron microscopy confirmed that bicarinalin can significantly decrease the density of H. pylori on gastric cells. We conclude that Bicarinalin is a promising compound for the development of a novel and effective anti-H. pylori agent for both curative and preventive use.

We have recently characterized bicarinalin as the most abundant peptide from the venom of the ant Tetramorium bicarinatum. This antimicrobial peptide is active against Staphylococcus and Enterobacteriaceae. To further investigate the antimicrobial properties of this cationic and cysteine-free peptide, we have studied its antibacterial, antifungal and antiparasitic activities on a large array of microorganisms. Bicarinalin was active against fifteen microorganisms with minimal inhibitory concentrations ranging from 2 and 25μmolL(-1). Cronobacter sakazakii, Salmonella enterica, Candida albicans, Aspergilus niger and Saccharomyces cerevisiae were particularly susceptible to this novel antimicrobial peptide. Resistant strains of Staphylococcus aureus, Pseudomonas aeruginosa and C. albicans were as susceptible as the canonical strains. Interestingly, bicarinalin was also active against the parasite Leishmania infantum with a minimal inhibitory concentrations of 2μmolL(-1). The bicarinalin pre-propeptide cDNA sequence has been determined using a combination of degenerated primers with RACE PCR strategy. Interestingly, the N-terminal domain of bicarinalin pre-propeptide exhibited sequence similarity with the pilosulin antimicrobial peptide family previously described in the Myrmecia venoms. Moreover, using SYTOX green uptake assay, we showed that, for all the tested microorganisms, bicarinalin acted through a membrane permeabilization mechanism. Two dimensional-NMR experiments showed that bicarinalin displayed a 10 residue-long α-helical structure flanked by two N- and C-terminal disordered regions. This partially amphipathic helix may explain the membrane permeabilization mechanism of bicarinalin observed in this study. Finally, therapeutic value of bicarinalin was highlighted by its low cytotoxicity against human lymphocytes at bactericidal concentrations and its long half-life in human serum which was around 15h.