Contamination Characteristics Of Antibiotic Resistance Genes In Freshwater Pond Aquaculture Products And Assessment Of Their Contribution To Human Exposure

The adverse effects of antibiotic residues on aquaculture systems and consumer populations have attracted global attention.China is a big country of aquaculture and consumption of aquatic products,and the Yangtze River Delta region is one of its major aquaculture areas.Long-term exposure to antibiotics in aquaculture ponds will affect the breeding environment and induce the appearance of antibiotic resistance genes(ARGs).Studies have shown that there are antibiotic residues in the freshwater aquaculture pond environment in the Yangtze River Delta region of China,and there are few studies on the resistance genes in freshwater aquaculture ponds in this region.Therefore,it is necessary to carry out an investigation on ARGs in freshwater aquaculture products and the water in this area to evaluate the contamination characteristics.At the same time,the horizontal and vertical transfer factors of ARGs were analyzed to understand the migration and diffusion rules of ARGs in aquatic products.Finally,based on the residual antibiotics and resistance genes in aquatic products,the contribution of edible aquatic products to human ARGs and antibiotic exposure was evaluated,respectively.The specific contents are as follows:(1)In order to evaluate the pollution characteristics of ARGs in freshwater pond aquatic products in the Yangtze River Delta region of China,9 freshwater aquaculture ponds in the Yangtze River Delta region of China were selected in 2019,and highthroughput q PCR technology was used to analyze the 33 kinds of ARGs in the intestinal and water of aquatic products,respectively.Four mobile genetic elements(MGEs)were detected,and the results showed that six types of ARGs were detected in the intestinal tract and water of aquatic products.Among them,sulfonamide ARGs is the main kind of ARGs in aquatic products and water.(2)In terms of horizontal transfer factors,the Pearson correlation analysis of the relative abundances of ARGs and MGEs detected in the gut of aquatic products showed that all four MGEs were significantly correlated with more than 3 ARGs.It suggested that MGEs might play an important role in the spread of ARGs.ARGs were found correlated with some MGEs,the higher the detection frequency of ARGs,the greater the possibility of horizontal transfer.For the vertical transfer factors,ARGs,MGEs and microorganisms under phylum classification with a detection frequency greater than50% were selected,and co-correlation analysis was performed using the relative abundance of the ARGs,MGEs and microorganisms.The results showed that only sul2 in ARGs was significantly correlated with microorganisms(Cyanobacteria),indicating that this bacterium may be a potential host of sul2,and sul2 can be vertically transferred and enriched through the phylum Cyanobacteria.However,considering that cyanobacteria were not the dominant flora in this study,the role of vertical transfer was limited.Only int1 in MGEs showed a significant correlation directly with bacteria in the community.This indicated that the ability of MGEs to promote the spread of ARGs in the gut of aquatic products is mainly reflected in int1.(3)Different exposure routes have different contributions to the total human exposure.In most cases,the exposure of aquaculture products was higher than that of drinking water and PM2.5,but lower than that of vegetables.Aquaculture products witnessed a high exposure contribution rate to human for tetracycline(tet M)and aminoglycoside(str B)ARGs.With the antibiotic residues in freshwater aquaculture products of the Yangtze River Delta,the daily exposure to antibiotics ingested through aquatic products was estimated,and the total body burden of antibiotics was estimated based on the antibiotic residues in urine;Range of product contribution to total daily exposure to antibiotics in different populations(children,adults,pregnant women)were explored.The results showed that nine target antibiotics were detected in the aquaculture products,but their concentrations were significantly lower than the MRLs.Enrofloxacin and sulfamethoxazole were of higher concentrations.Based on the metabolic concentration of antibiotics in urine,the total human exposure to antibiotics was back-calculated,and the exposure contribution rate of aquatic product consumption was estimated.The results illustrated that the consumption of aquaculture products has a high contribution rate to the human exposure of quinolones and macrolide antibiotics.Further results suggested that the risk of antibiotic exposure to consumers from consuming aquaculture products was lower than the risk of exposure to resistance genes.