Microplastic biofilms enrich antibiotic resistance genes in freshwater environments

Microplastics (MPs) and their associated biofilms, collectively known as the plastisphere, are emerging as environmental vectors of antibiotic resistance genes (ARGs). However, whether MPs preferentially retain health-relevant resistance genes remains unclear. This study conducted a systematic review and meta-analysis comparing ARG profiles on MPs and in surrounding freshwater environments. The meta-analysis revealed significant ARG enrichment in MP biofilms compared to water. Subgroup analyses further revealed that MPs enriched several mobile and enzyme-mediated resistance categories, including fosmidomycin, elfamycin, fosfomycin, β-lactams, aminoglycosides, macrolide-lincosamide-streptogramin, and multidrug resistance. In contrast, several categories were more abundant in freshwater environments, including mupirocin, sulfonamide, aminocoumarin, and trimethoprim. Chromosomal efflux-based mechanisms, such as tetracycline and fluoroquinolone resistance, showed minimal or no enrichment on MPs. At the gene level, both high-risk (Ranks I-II) and lower-risk (Ranks III-IV) ARGs were enriched on MPs relative to the surrounding water. Rank I genes were more frequently detected among enriched ARGs than Rank II genes, suggesting that MP biofilms may harbor diverse clinically relevant resistance determinants. Gene-level synthesis further identified numerous Rank I ARG subtypes across datasets spanning multiple antibiotic classes, indicating that enrichment involved multiple resistance determinants rather than a single dominant marker. Non-biodegradable polymers consistently demonstrated stronger enrichment than biodegradable ones. This pattern highlights the potential roles of polymer persistence, surface stability, and pollutant co-selection (e.g., plastic additives, antibiotics, heavy metals) may be drivers of ARG retention. By integrating key health-risk indicators, including mobility and environmental accessibility of resistance genes through established risk-ranking frameworks, these findings highlighted the plastisphere acts as a potential enrichment site for high-risk resistance genes and emphasize the need to incorporate MP-specific monitoring into One Health surveillance frameworks.