Effect of microplastics on oxytetracycline trophic transfer: Immune, gut microbiota and antibiotic resistance gene responses

Microplastics and antibiotics are prevalent and emerging pollutants in aquatic ecosystems, but their interaction in aquatic food chains remains largely unexplored. This study investigated the impact of polypropylene microplastics (PP-MPs) on oxytetracycline (OTC) trophic transfer from the shrimp (Neocaridina denticulate) to crucian carp (Carassius auratus), and determined the responses of gut microbiota and antibiotic resistance genes (ARGs) by macrogenomic sequencing. The carrier effects of PP-MPs promoted OTC bioaccumulation and trophic transfer, which exacerbated enteroclysis, vacuolization and eosinophilic necrosis of fish hepatocytes. The presence of PP-MPs significantly enhanced the inhibitory effect of OTC on the intestinal lysozyme activity and complement C3 level in shrimp and fish, as well as the hepatic immunoglobulin M level in fish (p < 0.05). The single exposure of OTC induced the abundance of Actinobacteria and Firmicutes in shrimp, and Bacteroidetes in fish, while the combination with MPs obviously increased the abundance of Actinobacteria in shrimp and Firmicutes in fish, which caused disturbances in carbohydrate, amino acid and energy metabolism. Moreover, OTC exacerbated the enrichment of antibiotic resistance genes (ARGs) in aquatic animals, and the carrier effects of PP-MPs obviously increased the diversity and abundance of ARGs and facilitated the trophic transfer of teta and tetm in the co-exposure group. Tetracycline (tetm, tetb, tet36, tetc) and streptomycin (aac6ib) resistance genes were significantly positively correlated with the potential hosts Clostridium, unclassified_f_Clostridiaceae and Bacteroides. Our findings disclosed the impacts of PP-MPs on the mechanism of antibiotic toxicity in the aquatic food chain and further emphasized the importance of the trophic transfer of ARGs by the gut microbiota, which contributed to a deeper understanding of the potential risks posed by combined pollution of MPs and antibiotics on aquatic ecosystems.

Granphical Abstract