Study On Distribution And Environmental Competition Of Antibiotic-resistant Escherichia Coli In Typical Estuary Environments

In recent years,antibiotic resistant genes(ARGs)and antibiotic resistant bacteria(ARB)have been detected in many countries and regions,indicating that the globalization phenomenon of antibiotic resistance has been initially apparent.Estuary ecosystems are ecotones between rivers and oceans and key areas for understanding antibiotic resistance fate after release into aquatic environments.However,the distribution and dynamic characteristics of antibiotic resistance in estuary environment are still unclear,and the effect of estuarine physicochemical conditions on antibiotic resistance remains to be studied.In order to solve the above problems,the Liaohe and Daliaohe estuaries were selected as the representative areas of estuary environment.Firstly,a method for rapidly assessing the antibiotic resistance of typical pathogen Escherichia coli(E.coli)in estuaries and coastal marine environments was established.Secondly,this method was applied to analyze the antibiotic resistance levels of E.coli in summer and winter in the Liaohe and Daliaohe estuaries.High performance liquid chromatography-mass spectrometry was used to detect the concentrations of antibiotics.Furthermore,multiple environmental factors were analyzed to discover the main factors which affect the dissemination of antibiotic resistance.The experiment of competition simulation was designed according to influence factors.The results of this study demonstrated the following:(1)Sulfonamides,quinolones and tetracyclines antibiotics were commonly detected in the Liaohe and Daliaohe estuaries,but the concentrations of antibiotics were much lower than those in the inland environment such as urban sewage and rivers.(2)Although the concentrations of antibiotics were very low,sulfonamide-resistant E.coli was widespread in the estuaries.There was significant attenuation of sulfonamide-resistant E.coli abundances in the process of migration from the inland rivers to the ocean,suggesting that estuaries play a natural attenuation role in inhibiting dispersal of sulfonamide-resistant E.coli populations.(3)In both water and sediment,the concentrations of antibiotics and the abundances of sulfonamide-resistant E.coli in winter were higher than those in summer in the Liaohe and Daliaohe estuaries.(4)The contribution of antibiotics on the distribution and migration of sulfonamide-resistant E.coli in the estuaries was lower than those of heavy metals and physicochemical parameters(salinity,temperature,and pH).Heavy metals can enhance the competitive advantage of antibiotic-resistant E.coli,while antibiotics can not which shows that other external factors may share or substitute the role of antibiotic and contribute to the propagation of antibiotic resistance when the antibiotic concentration is low.The main pathway of antibiotic resistance proliferation may switch from active transmission,which is dominated by antibiotics,to passive transmission,which is motivated and affected by other external factors.(5)In oligotrophic estuaries,sulfonamide-resistant E.coli exhibited a stronger adaptability to increasing salinities resulting in increasing migration ability.Therefore,although the estuary could play a natural attenuator role in limiting the dispersal of sulfonamide-resistant E.coli,it could improve the competitive advantage of ARB,thereby increasing the risk of antibiotic resistance global proliferation.