Catanionic surfactant mixtures form a wide variety of organized assemblies and aggregates with improved physicochemical and biological properties. The green catanionic mixture NαNω-Bis(Nαcaproylarginine) α,ω-propyldiamide (C3(CA)2):Lichenysin (molar ratio 8:2) showed antimicrobial synergies against Yersinia enterocolitica, Bacillus subtilis, Escherichia coli O157:H7, and Candida albicans. Flow cytometry and viability studies indicated that this catanionic mixture increases the probability of Y. enterocolitica (38.2%) and B. subtilis (17.1%) cells entering a viable but nonculturable state. Zeta potential showed that one of the cationic charges of C3(CA)2 is neutralized by Lichenysin. An isotherm study demonstrated the formation of a stable aggregate between the two surfactants. The catanionic aggregate was able to interact with bacterial phospholipids. The lowest hemolysis (22.1 μM) was obtained with the catanionic mixture, although an irritant potential (0.70) was characterized. According to the therapeutic index, the C3(CA)2:Lichenysin mixture was the formulation least toxic to eukaryotic cells. Partial neutralization of C3(CA)2 by Lichenysin modified the mode of action that enhances the transition of bacterial cells into a viable but nonculturable state (VBNC) and improved the cell selectivity.
Keywords: Langmuir balance; Lichenysin; VBNC; antimicrobial activity; biosurfactant; catanionic mixtures; flow cytometry; gemini surfactants.