An Ionic Liquid Facilitates the Proliferation of Antibiotic Resistance Genes Mediated by Class I Integrons

Ionic liquids (ILs), as "environmentally friendly" replacements for industrial volatile organic solvents, have been widely and recently applied in the chemical industry. However, few data have been collected regarding the toxicity and potential environmental effects of ILs, which are fairly important for preparing for their potential release into the environment. In this study, the IL 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]) was tested for its ability to promote the proliferation and dissemination of antibiotic resistance genes (ARGs) in environmental bacteria. In freshwater microcosms, [BMIm][PF6] (0.5 g/L) significantly enhanced the abundance of the sulI gene (500-fold greater than in untreated controls). Meanwhile, [BMIm][PF6] significantly increased the abundance of class I integrons, which play a key role in ARC dissemination. A positive correlation (p < 0.01) between the intI and sulI genes suggested that [BMIm][PF6]-facilitated sulI propagation was mediated by class I integrons. This idea was supported by sequencing, which showed the sulI locus in the 3' region of class I integrons. Class I integron transfer experiments between different indigenous strains of Alcaligenes sp. (SMXR) and Acinetobacter sp. (Str(R)) were conducted to show that the horizontal transfer frequency of class I integrons was up to 88-fold higher in the presence of an IL. An IL increased cell membrane permeability as evidenced by flow cytometry, thereby assisting sulI gene transfer mediated by class I integrons. This is the first report that ILs facilitate the proliferation of ARGs in environmental bacteria and thus increase risks to public health.