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Gut microbiome and metabolic responses of adult zebrafish (Danio rerio) to the co-exposure of polyethylene microplastics and levofloxacin
Summary
Scientists found that when zebrafish were exposed to both microplastics and a common antibiotic together, something surprising happened: the microplastics actually soaked up some of the antibiotic, which protected the fish's gut bacteria from damage. But here's the catch — even though the gut microbiome looked healthier, the fish still suffered worse overall health effects, including stress signals and metabolic disruptions not seen with either exposure alone. This suggests that a "stable" gut microbiome doesn't always mean a body is truly healthy, which matters as humans increasingly encounter both microplastics and antibiotic residues in food and water
The co-occurrence of microplastics (MPs) and antibiotics in aquatic environments poses complex ecological risks. This study investigated the combined toxicity of polyethylene microplastics (PE MPs) and levofloxacin (LEV) in zebrafish using integrated untargeted metabolomics and gut microbiome profiling. Zebrafish were exposed to environmentally relevant concentrations of LEV (0.1 μg/L, 1 μg/L, 100 μg/L), PE (1 mg/L), and their combinations for 96 h. LEV exposure produced concentration-dependent metabolic toxicity, progressing from energy conservation at 0.1 μg/L to inflammatory activation at 1 μg/L, and ultimately to system-wide metabolic perturbation at 100 μg/L. PE independently disrupted oxidative stress and membrane integrity pathways. Co-exposure generated emergent interactive effects exceeding additive predictions, with PE + LEV 0.1 μg/L affecting 387 metabolites versus 245 for LEV alone. Crucially, co-exposure elicited synergistic toxicity with unique metabolic fingerprints-including neuroendocrine activation (dynorphin B) and mTOR signaling modulation-that were absent in individual treatments. Conversely, microbiome analysis revealed an antagonistic interaction; while LEV alone caused significant dysbiosis and enrichment of resistant taxa, co-exposure stabilized microbial diversity and composition, likely due to LEV adsorption onto PE particles reducing luminal bioavailability. These findings highlight a "microbiome-host interaction paradox": PE mitigates antibiotic-induced gut dysbiosis yet exacerbates host systemic toxicity through mechanisms of epithelial barrier disruption and pharmacokinetic modulation. This study demonstrates that microbiome stability does not reliably predict host physiological health under multi-stressor conditions, underscores the importance of integrative, multi-omics approaches to assess the emergent risks of complex environmental mixtures.