Study On The Combined Toxicity Effect Of AgNPs And Typical Antibiotics On E.coli And Its Combined Resistance

Nano silvers?AgNPs?are widely used in many fields because of their high antibacterial properties and reduction of endurance.Therefore,it is inevitable that organisms in the environment will be exposed to the mixtures of AgNPs and other pollutants,posing potential risks for the ecological environment and economy.Antibiotics in the environment have the characteristics of "persistence-combination-low dose”.Persistence will cause antibiotic residue,combination will produce synergism,antagonism,and low dose will bring a stimulating effect.In addition,bacterial resistance is a serious threat to public health,economic growth and global economic stability.The G20 summit has defined antibiotic resistance as one of the factors affecting the world.However,bacteria can obtain resistance by binding to the antibiotic resistance gene?ARGs?on the plasmid,and the level of plasmid transfer is affected by many environmental factors.There has been some reports on the mechanism of toxicity of AgNPs and antibiotics to bacteria,but the combined toxicity mechanism of the combination of their mixture is still not clear,whether the combined toxicity.Based on the above facts,this paper uses E.coli and B.subtilis as the model bacteria,and sets Ag NPs,sulfonamides,tetracycline and penicillins as objects,to study the toxic source of AgNPs on LB medium;the mechanism of the single/combined toxicity of AgNPs and above antibiotics on E.coli and their effects on the binding and metastasis of RP4 plasmid;and the influence of different incubate system to Hormesis effect.This paper analyzed the toxic mechanism of AgNPs and typical antibiotics on E.coli,and state the mechanism of combined toxicity based on oxidative stress.QSAR model based on Ebinding and lg?1/EC50?was introduced to analyze the combined toxicity and the resistance relation of AgNPs and antibiotics.This paper provided a new insight to risk assessment and management of ecological environment and economy.The main study contents and conclusions are as follows:?1?A case study of AgNPs toxicity in LB MediumThe composition and proportion of silver ions(AgCl_x^1-x)in LB medium at different temperatures and NaCl concentrations were calculated.And the toxicities of AgNO₃ to E.coli and B.subtilis were determined.The results showed that the ratio of Ag2-was always the highest in LB medium with different NaCl concentration at room temperature and 37?.The toxicity of AgNO₃ to E.coli and B.subtilis will not change with the increase of Cl-concentration in the system.And the maximum concentration of Ag + in Cl--medium did not reach to the lethal dose.Therefore,the toxicity of AgNO3 or AgNPs in the Cl-containing culture system depend on Ag2-.?2?The single toxicity of AgNPs on E.coliThe single toxic effects of AgNO₃ and AgNPs to E.coli on LB and MH medium,and the effects of AgNO₃ and AgNPs on the conjugative transfer of RP4 plasmids were determined.The results showed that the toxicity of AgNPs to Escherichia coli was lower than that of AgNO₃ in LB medium,and the inhibition rate increased with the increase of concentration.AgNPs and AgNO₃ on the growth of E.coli were only occurring for a specific time in the MH medium.AgNPs and AgNO₃ promoted the binding and metastasis of RP4 plasmid,and there was a peak.?3?The single toxicity of antibiotics on E.coliThe single toxicity of typical antibiotics to E.coli in LB and MH medium and the effect on the binding and metastasis of RP4 plasmids were determined.The results showed that the inhibitory rate of typical antibiotics in Escherichia coli increased with the increase of the concentration in the LB medium,and the toxicity rates were penicillins> tetracycline> sulfonamides.Typical hormones on E.coli hormesis occur only at specific times and in MH medium.The typical antibiotics promoted the binding and metastasis of RP4 plasmid,and reached the peak with the change of concentration,and finally inhibited the binding and metastasis of RP4 plasmid.?4?The combined toxicity of AgNPs and antibiotics on E.coliThe combined toxicity of AgNPs and antibiotics on E.coli and the conjugative transfer of their mixture were determined.The results showed that the inhibition of Ag NPs and typical antibiotics increased with the increase of the concentration of the mixed solution regardless their proportions.When the mixtures equitoxic,the combined toxicity of AgNPs and sulfonamides was mainly synergism;of AgNPs and TCs was mainly synergism;of AgNPs and P.Gs was mainly addition.Combined with P.Gs,the toxic effects were mainly antagonistic.ROS level is considered to be the important factor that influencing the combined toxicity and joint metastases based on the oxidative stress.AgNPs combined with antibiotics all promoted the binding and metastasis of RP4 plasmid,this promotion increased with the increase of concentration,and then decreased.There was no liner relation between the combined toxicity and the binding and metastasis of RP4 plasmid.However,their RU and TU values had good linear relationship,which is consistent in general,but not significant.