UV-aged biodegradable and non-biodegradable microplastics further enhance horizontal transfer of antibiotic resistance plasmids both in vitro and in intestinal flora.

Microplastics is a well-known environmental contaminant that have raised concerns regarding their role in spreading antibiotic resistance genes (ARGs). This study investigates the effect of ultraviolet (UV) aging of 100 nm petroleum-based (polystyrene, PS) and bio-based (polylactic acid, PLA) microplastics on the horizontal transfer of multidrug resistance plasmids. Both PS and PLA significantly increase the frequency of horizontal spread of ARGs, and UV aging of both PS and PLA microplastics further enhance this frequency by 4- to 20-fold, implying that environmental elements, including UV radiation, may increase the ecological danger caused by microplastics. UV aging significantly alters the surface properties of both PS and PLA microplastics and disrupted the integrity of bacterial cell membranes. Moreover, UV-aged microplastics increased cellular uptakes and exacerbated oxidative stress in bacteria by elevating ROS levels and SOD activity. In addition, UV-aged microplastics improved bacterial energy metabolism, providing additional ATP for conjugation process. Finally, UV-aged microplastics aggravated oxidative stress and intestinal inflammation in gut which further promoted the plasmid conjugation rate in vivo by 3.5-fold. The findings not only draw attention to the important role of UV-aged microplastics in permitting ARG spread but also urge thorough risk assessments of degradation of microplastics on public health and ecosystems.