In the past two decades, numerous families of genetically encoded antimicrobial peptides (AMPs), from all living organisms, have been described [1,2]. They are conserved components of the innate immune response, and represent the first host defence line against microbial infections. Alghough AMPs show a marked variation in size, sequence and structure, most of them are polycationic and fold into an amphipathic helical or beta-sheet structure, a feature which aids their interaction and insertion into microbial membranes that are believed to be the principal target for their killing mechanism. Before reaching the negatively-charged bacterial membrane, AMPs need to bind, via electrostatic interactions, the anionic components of the microbial cell surface and diffuse through the cell wall. The growing emergence of multidrug-resistant (MDR) microorganisms makes it increasingly difficult to treat infections. These infections include those associated with Pseudomonas aeruginosa, which is hard to eradicate, especially in patients with a compromised immune system[3]. Amphibian skin is one of the richest sources for such AMPs, but only a few studies on their in vivo activity and mode of action have been reported. Here we investigated: (i) the activity and mechanism underlying the killing of short AMPs from frog skin (e.g., temporins and esculentin fragments[4] ) on a MDR clinical isolate of P. aeruginosa; (ii) their in vivo antimicrobial activity and mode of action, using the mini-host model of Caenorhabditis elegans[5]. Our data revealed that in vivo, both temporin-1Tb and esculentin(1-18) were highly active in promoting the survival of pseudomonas-infected nematodes, although temporin-1Tb did not show significant activity in vitro, under the experimental conditions used. Importantly, esculentin(1-18) permeated the membrane of Pseudomonas cells within the gut of the infected nematode. To the best of our knowledge, this is the first report showing the ability of a CAMP to permeate the microbial membrane within a living organism. Besides shedding light on a plausible mode of action in vivo of frog skin AMPs, our data suggest these peptides as templates for the design and development of new anti-infective agents.
References
1 Zasloff, M. (2002) Nature. 415, 389-395
2 Brown, K. L., and Hancock, R. E. (2006) Curr Opin Immunol. 18, 24-30
3. R.E. Hancock And D.P. Speert. Drug Resist. Updat (2000), 3, 247-25
4. M.L. Mangoni et al. Antimicrob. Agents and Chemother. (2008), 52, 85-91
5 T. I. Moy et al. Proc. Natl. Acad. Sci. USA(2006), 103,10414-10419
