Mechanism of Antibacterial Activity of Choline-Based Ionic Liquids (CAGE)

Abstract

The continued emergence of antibiotic-resistant organisms has severely depleted our arsenal of effective antimicrobials. Ionic liquids (ILs) show great promise as antibacterial agents but understanding the mechanism of attack on bacterial cells is key to ensuring that design of IL-based biocides impart maximum efficacy with minimal toxicity, while also avoiding the potential for the target organisms to become resistant. Here we report the antibacterial attributes of a set of choline and geranate (CAGE)-based ILs and identify the mechanism by which they interact with the Gram-negative cell wall of Escherichia coli. CAGE is envisaged as an antimicrobial agent to treat topical infections in skin. Our earlier work has shown that CAGE is highly effective across a breadth of bacterial, fungal, and viral species and is benign to human cells. This combination makes CAGE an ideal antimicrobial for human use. Four CAGE variants with varying ratios of choline and geranic acid were synthesized and tested for their antibacterial activity (1:4, 1:2, 1:1, and 2:1 choline:geranic acid). The minimum bactericidal concentration required to kill E. coli correlated with the geranic acid content. Using molecular dynamics (MD) simulations, we identified the mechanism of CAGE action on the E. coli membrane, namely that choline is attracted to the negatively charged cell membrane and consequently inserts geranic acid into the lipid bilayer. The disruption of the cell membrane was confirmed with propidium iodide staining via flow cytometry and scanning electron microscopy. Fourier Transform infrared spectroscopic analysis of treated cells showed an altered lipid profile similar to phase transition, indicating the disruption of the lipid bilayer conformation. E. coli cells repeatedly exposed to CAGE did not exhibit resistance. This study provides the fundamental mechanism of the action of choline-based ILs on Gram-negative bacteria and demonstrates the promise of CAGE as a powerful antimicrobial agent to treat infections.

Design Principles of Ionic Liquids for Transdermal Drug Delivery

“…ILs of Geranic Acid with Choline Alternatives : Quaternary amines were reacted with recrystallized geranic acid in a 1:2 molar ratio at 40 °C for 12 h, similarly to the CAGE synthesis reported previously . A rotary evaporator was then used to dry the resulting ionic liquids at 20 mbar at 60 °C for 2 h. The residual water was removed under reduced pressure at 60 °C for 48 h.…”

Studies on the Antibacterial Influence of Two Ionic Liquids and their Corrosion Inhibition Performance

“…These results indicate the bactericidal effect of ionic liquid [OH-EMIm]Cl and the inhibition efficiency were dependenton the ionic liquid concentration. In general, the antibacterial influence of the ionic liquids is attributed to the attraction of the ionic liquid species to the cell membrane causing its disruption [26]. The inhibition efficiency of the bacterial growth in the presence of different concentrations of [EMIm]Cl as a function of time is displayed in Figure 5.…”

Modelling and prediction of the thermophysical properties of aqueous mixtures of choline geranate and geranic acid (CAGE) using SAFT-γ Mie

“…RTILs are usually dened as organic salts with 1 : 1 cation : anion molar ratio and melting points below 100 C, while DESs are more generally dened as mixtures of charged and neutral components. A series of studies of DESs/RTILs for a number of anion/cation/solvent combinations have been tested, [4][5][6][7] and mixtures of choline and generate (CAGE) were shown to offer promising therapeutical properties, including powerful antibacterial activity against a variety of drug-resistant bacteria, fungi and viruses, low toxicity, and enhancement of the transdermal delivery of proteins and antibacterial drugs. The mixture with a 1 : 2 choline : geranate mol ratio was shown to be especially effective.…”