Polymer type and aging drive the selective enrichment of antibiotic resistance genes and pathogens in microplastics biofilms.

Microplastics (MPs) biofilms are critical vectors for antibiotic resistance in aquatic environments. In this study, in situ incubation coupled with metagenomic sequencing was employed to investigate microbial colonization patterns, antibiotic resistance gene (ARG) profiles, and mobile genetic element (MGE) dissemination characteristics of biofilms on MPs surfaces of different polymer types and aging states within a unique wetland ecosystem. Results demonstrated that microorganisms preferentially colonized the hydrophobic surface of conventional polypropylene (PP) over biodegradable polylactic acid (PLA). Aging treatments further enhanced MP-microbe interactions. Microbial community analysis revealed selective enrichment of microbial communities in MPs biofilms, including clinically relevant pathogens such as Acinetobacter baumannii. Notably, despite showing lower microbial colonization, PLA enriched a higher abundance of priority antibiotic-resistant pathogens and high-risk ARGs, which further amplified following environmental aging. Co-occurrence network analysis identified seven key MGEs strongly correlated with multiple ARGs and exhibited the highest abundance on PLA-derived biofilms, indicating a high potential for horizontal gene transfer mediating the propagation of antibiotic resistance. Furthermore, Enterobacteriaceae were identified as critical co-hosts of ARGs and MGEs within the plastisphere, potentially playing a central role in maintaining antibiotic resistance. Our findings highlight a significant ecological threat from biodegradable and aged MPs in amplifying antibiotic resistance.