Effects of Conventional Surfactants on the Activity of Designed Antimicrobial Peptide.

In this paper, the interaction between a designed antimicrobial peptide (AMP) G(IIKK)3I-NH2 (G3) and four typical conventional surfactants (SDS, C16TAB, C12EO23 and C14DMAO) have been studied through surface tension measurement, circular dichroism (CD) spectroscopy. The antimicrobial activities of AMP/surfactant mixtures have also been studied with gram-negative E. coli, gram-positive S. aureus, and fungus C. albicans. The cytotoxicity of the AMP/surfactant mixtures has also been assessed with NIH 3T3 and HSF cells. The surface tension data showed that AMP/SDS mixture was much more surface active than SDS alone. CD results showed that G3 conformation changed from random coil, to -sheet, then to alpha-helix with increasing SDS concentration, showing a range of structural transformation driven by the different interactions with SDS. The antimicrobial activity of G3 to gram-negative and gram-positive bacteria decreased in the presence of SDS due to the strong interaction of electrostatic attraction between peptide and surfactant. The interaction between G3 and C16TAB, C12EO23, C14DMAO were much weaker than SDS. As a result, the surface tension of surfactants with G3 did not change much, neither were the secondary structures of G3. The antimicrobial activities of G3 were little affected in presence of C12EO23, slightly improved by C14DMAO and clearly enhanced by cationic surfactant C16TAB due to its strong cationic and antimicrobial nature, consistent with their surface physical activities as binary mixtures. Although AMP G3 didn't show activity to fungus, the mixtures of AMP/C16TAB and AMP/C14DMAO could kill C. albicans at high surfactant concentration. The mixtures had rather high cytotoxicity to NIH 3T3 and HSF cells although G3 is nontoxic to cells. Cationic AMPs can be formulated with nonionic, cationic and zwitterionic surfactants during product development, but care must be taken when AMPs are formulated with anionic surfactants, as the strong electrostatic interaction may undermine their antimicrobial activity.