Enrichment of high-risk antibiotic resistance genes on microplastics in freshwater environments: A meta-analysis

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.