Antibiotic resistance genes are more abundant in microplastic textile biofilms than natural cotton biofilms in freshwater.

UNLABELLED: Microplastic fibers (MPFs) are widespread pollutants in freshwater systems, providing artificial surfaces that facilitate microbial attachment and the potential spread of antibiotic resistance genes (ARGs). We compared bacterial colonization on natural cotton fibers with that on synthetic MPFs (Kevlar, acrylonitrile, polyester, and nylon) incubated in river and lake water. Bacterial biomass and community composition were analyzed using epifluorescence microscopy, scanning electron microscopy, and 16S rRNA sequencing, while the presence and relative abundance of key ARGs (blaNDM-1, blaKPC, and blaOXA-48) were quantified using qPCR. Cotton fibers developed substantially higher biofilm loads than any synthetic MPF, supporting dense and taxonomically diverse microbial communities. In contrast, synthetic MPFs supported lower levels of bacterial colonization but exhibited significantly higher levels of ARG enrichment, with blaOXA-48 showing the highest relative abundance. Several taxa, including Fluviicola, Sphingobium, Nitrospira, Schlesneria, and TRA3-20 (Burkholderiaceae), harbored ARGs across all synthetic MPF types. Overall, the findings highlight a clear difference in biofilm quantity and ARG prevalence, with cotton accumulating the most biofilm but having the lowest ARG burden, whereas synthetic MPFs supported ARG-associated bacteria despite lower colonization. These results suggest that synthetic MPFs may play a disproportionately large role in the environmental dissemination of antibiotic resistance due to their mobility and affinity for ARG-harboring microbial communities in freshwater ecosystems.

IMPORTANCE: Microplastic fibers (MPFs) are widespread in freshwater systems but remain underexplored as reservoirs and vectors of antibiotic resistance. This study reveals that synthetic MPFs serve as enriched niches for bacteria harboring relevant antibiotic resistance genes (ARGs), in contrast to natural fibers like cotton. By combining high-resolution microscopy, 16S rRNA gene sequencing, and quantitative PCR, we demonstrate that MPFs selectively support ARG-bearing taxa, including Fluviicola and Sphingobium, across multiple fiber types. These findings suggest that MPFs in aquatic environments may facilitate horizontal gene transfer and contribute to the environmental dissemination of antibiotic resistance. Understanding microbial colonization patterns on MPFs is critical for assessing the ecological and public health risks posed by microplastic pollution.