Magnetic ionic liquids: interactions with bacterial cells, behavior in aqueous suspension, and broader applications

Evaluating the capacity of magnetic ionic liquids for separation and concentration of non-enveloped viral particles and free viral genomic RNA

Magnetic ionic liquids (MILs) have proven effective as capture reagents for foodborne bacterial pathogens; however, there are currently no published studies regarding their use with foodborne, non-enveloped viruses. In this study, a protocol was evaluated for capture and recovery of bacteriophage MS2, a human norovirus surrogate, and purified viral genomic single stranded RNA (ssRNA) from an aqueous suspension using MILs. Transition metal-based MILs showed similar capture and recovery efficiency for both targets. A rare earth metal-based MIL showed much greater capture efficiency than the transition metal-based MILs, but displayed similar recovery. All tested MILs showed slightly higher capture and recovery efficiency for free RNA in comparison to intact virus, though overall trends were similar, and most MILs could recover both targets at as little as 102 PFU/mL intact MS2 or copies/mL purified RNA. A plaque assay confirmed that contact with MILs did not significantly reduce viral infectivity. Adjusting MIL volume gave no significant changes in capture or recovery, likely due to interplay between volume for the hydrophobic MIL and dispersion. Reducing the elution volume gave a slight increase in recovery, indicating MILs could be used for target enrichment after further optimization. MILs could also capture MS2 from romaine lettuce rinsate at comparable or even higher levels than from pure suspension, though loss in recovery was observed when the rinsate was prepared in an alkaline elution buffer. Overall, these results demonstrate the potential utility of MILs as concentration reagents for foodborne viruses, particularly for in-field applications.

Effect of Non-natural Hydrophobic Amino Acids on the Efficacy and Properties of the Antimicrobial Peptide C18G

Antimicrobial peptides (AMPs) have been an area of great interest, due to the high selectivity of these molecules toward bacterial targets over host cells and the limited development of bacterial resistance to these molecules through evolution. The peptides are known to selectively bind to bacterial cell surfaces through electrostatic interactions, and subsequently, the peptides insert into the cell membrane and cause local disruptions of membrane integrity leading to cell death. Previous experiments showed that replacing the Leu residues in the AMP C18G with other naturally occurring hydrophobic residues resulted in side-chain-dependent activities. This work extends the investigation to non-natural hydrophobic amino acids and the effect on peptide activity. Minimal inhibitory concentration (MIC) results demonstrated that amino acid substitutions containing long flexible carbon chains maintained or increased antimicrobial activity compared to natural analogues. In solution, the peptide showed aggregation only with the most hydrophobic non-natural amino acid substitutions. Binding assays using Trp fluorescence confirm a binding preference for anionic lipids while quenching experiments demonstrated that the more hydrophobic peptides are more deeply buried in the anionic lipid bilayers compared to the zwitterionic bilayers. The most effective peptides at killing bacteria were also those which showed some level of disruption of bacterial membranes; however, one peptide sequence exhibited very strong activity and very low levels of red blood cell hemolysis, yielding a promising target for future development.