Microplastics Pose an Elevated Antimicrobial Resistance Risk Than Natural Surfaces via a Systematic Comparative Study of Surface Biofilms in Rivers

The pervasive presence of antimicrobial resistance (AMR) in various ecosystems threatens global health, especially in persistent biofilm states. Both anthropogenic and natural surfaces in environments provide ideal habitats for biofilm development. Microplastics (MPs), as emerging and rapidly proliferating anthropogenic pollutants, are of particular concern due to their unique physicochemical properties and ubiquity across environments. However, it remains unclear whether biofilms on MPs pose a higher AMR risk compared with natural surfaces. Here, we employed an integrative approach combining phenotypic and genotypic AMR analysis via single-cell spectroscopy and high-throughput quantitative PCR to systematically compare AMR risks on 5 MPs (polyethylene, polystyrene, poly(vinyl chloride), polylactic acid, and Tetra Pak) and 3 natural surfaces (wood, rock, and glass) in an urban aquatic ecosystem. Our results revealed that MPs harbored a higher proportion of metabolically active antibiotic-resistant bacteria and more high-risk antibiotic resistance genes than natural surfaces. By incorporating phenotypic and genotypic AMR with three additional biofilm-related risk factors, including biofilm biomass, microbial activity, and pathogen abundance, the health risk of AMR was quantified and found to be highly dependent on surface types. MPs exhibited, on average, a 10-fold higher health risk than natural surfaces. A structural equation model further identified surface hydrophobicity and microbial diversity as pivotal factors determining AMR risks across different surfaces. This systematic comparison provides new insights into the real-world environmental impact of MPs pollution and underscores the necessity of integrating plastic pollution control into AMR management strategies.