Occurrence And Risk Assessment Of Antibiotic Resistance Genes In Typical Chicken Farms And Surrounding Soils

At present,animal manure is considered to be an important reservoir for antibiotics,antibiotic resistance genes(ARGs)and antibiotic resistance bacteria(ARB).In recent years,more and more veterinary antibiotics have been widely used in large-scale livestock and poultry farming.The extensive use and abuse of antibiotics have induced the rise of ARB levels and promoted the spread of ARGs in the environment.However,the existing researches mainly focused on the content characteristics of ARGs in the farms and surrounding soil,less attention was paid to the dynamic migration and diffusion process of ARGs to the surrounding soil and environmental impact factors,and the risk assessment of antibiotics and antibiotic resistance was still initial stage.Therefore,this study focused on chicken manure and surrounding gradient soil samples from large-scale chicken farms,studied the occurrence of ARGs in the livestock and poultry breeding environment,explored the bacterial community structure and various environmental factors(antibiotics,heavy metals and environmental Physicochemical parameters)Impact on the of ARGs composition,and scientifically evaluated the risk of antibiotics and antibiotic resistance pollution in the breeding environment.Therefore,this study mainly aims at the samples of chicken manure and surrounding gradient soil in large-scale chicken farm to study the influence of ARGs abundance and diversity,bacterial community structure and environmental factors(antibiotics,heavy metals and environmental physicochemical parameters)on the distribution characteristics of ARGs composition,and scientifically assess the risk of antibiotics and antibiotic resistance pollution in the breeding environment.The main conclusions are as follows:(1)The high-throughput fluorescence quantitative PCR technique was used to characterize the distribution characteristics of five categories of ARGs and MGEs in chicken manure and surrounding gradient soils.The results showed that MLSB,sulfonamides and tetracycline ARGs have a high incidence and were the main gene types in chicken farms.A variety of ARGs were detected in high concentrations in chicken manure samples,indicating that livestock manure is an important source of ARGs in the surrounding soil.The correlation between MGEs and ARGs indicates that MGEs play an important role in the spread and spread of ARGs.(2)Redundancy analysis(RDA)and correlation analysis were used to explore the influence of external environmental factors such as antibiotics,heavy metals and conventional physicochemical parameters on the abundance changes and distribution characteristics of ARGs.Studies have shown that there are significant correlations between the abundance changes of some ARGs and the concentration levels of various antibiotics,some heavy metals and physicochemical parameters(P<0.05),which implies that relevant environmental factors have selective pressure on bacterial resistance.And multiple environmental factors may play a common role in selecting ARGs.(3)The 16s rRNA high-throughput sequencing was used to analyze the diversity and occurrence of bacterial community structure in chicken manure and soil samples from chicken farms.RDA and network analysis were used to explore the co-occurrence relationship between bacterial communities and ARGs.The study found that,due to the nature of the soil itself,the diversity of bacterial community structure in soil samples was significantly higher than that in chicken manure samples(P <0.05).Cluster analysis showed that the predominant flora in the soil and chicken manure samples were different at the phylum and genus levels.The collinear model of bacterial communities and ARGs showed that multiple ARGs havd the same potential host bacteria,and the spread of host bacteria could affect the occurrence of corresponding ARGs.(4)The RQ method was used to evaluate the potential risk of antibiotics remaining in the soil for resistance selection of the ecosystem.The results showed that the ecological risk of the near soil around the chicken farm is higher than that of the control remote soil,and livestock and poultry feces produced different degrees of antibiotic pollution on the surrounding soil.Since the complete risk assessment benchmark for antibiotic resistance has not yet been formed,this study combined with the way in which ARGs multiply and spread in the environment,conducted a preliminary assessment of the risk of antibiotic resistance,and obtained drfA1,tetH and tetQ have a higher risk of drug resistance.Control measures have been proposed in many ways to reduce the ecological risks of antibiotics and antibiotic resistance.