The microbial toxicity of quaternary ammonium ionic liquids is dependent on the type of lipopolysaccharide

In the present study the toxicity of theophylline-based quaternary alkylammonium ionic liquids and their precursors was investigated in relation to smooth and rough Escherichia coli strains. We assumed that the microbial toxicity of the studied amphiphilic compounds was affected by the composition of the lipopolysaccharide (LPS) of Gram-negative bacteria. Our hypothesis was verified using K-12 (smooth) and R1−R4 (rough) strains which are characterised by differences in LPS, especially in the O-antigen region. Interactions between ionic liquids and DNA were also investigated. Digestion by Fpg protein was performed to evaluate DNA damage following both indirect action of ionic liquids and via lipid peroxidation. The results revealed differences in sensitivity to the tested compounds between smooth and rough strains, as well as differences in peroxidase activity and lipid peroxidation. The ionic liquids did not interfere with DNA in vitro, and intracellular DNA damage that occurred after treatment was probably caused by lipid peroxidation and oxidative stress.