Nanoplastics promote the dissemination of antibiotic resistance through conjugative gene transfer: implications from oxidative stress and gene expression

Abstract

Antibiotic resistance is a growing challenge and a major public health concern worldwide. Nanoplastics, which are ubiquitous in aquatic ecosystems, may cause a potential risk to the dissemination of antibiotic resistance genes (ARGs) in bacteria. However, the extent to which nanoplastics can cause an increase in antibiotic resistance by the regulation of the conjugative transfer of ARGs within bacteria remains unknown. In this study, polystyrene nanoplastics (PSNPs) with small sizes (S-PSNPs) and large sizes (L-PSNPs) were applied at a wide concentration range of 0.1–200 mg L⁻¹ to investigate their effects on plasmid-mediated conjugative transfer of ARGs between E. coli strains. The results revealed that S-PSNPs significantly enhanced the conjugative transfer frequency of the RP4 plasmid up to 1.51 fold at the 10 mg L⁻¹ exposure level compared with untreated cells; however, L-PSNPs generally caused no significant effect. We also employed multiple approaches to reveal the mechanisms, which demonstrated that PSNPs facilitated the conjugative transfer of ARGs by inducing excessive reactive oxygen species and oxidative stress, increasing cell membrane permeability, up-regulating the expression of mating pair formation genes (trbBp and traF) and DNA transfer and replication genes (trfAp and traJ), and down-regulating the global regulatory gene expression (korA, korB, and trbA). These findings provide insights regarding the contributions and the underlying mechanisms of nanoplastics to the dissemination of ARGs, and are helpful for the evaluation of the public health and environmental and ecological risks caused by nanoplastics.