The Effect Of Typical Antibiotics On Escherichia Coli Antibiotic Resistance And Its Mechanism

Antibiotics are widely used to treat bacterial infections.As antibiotics are abused,bacteria have evolved antibiotic resistance genes and can spread rapidly through vertical and horizontal transfer,posing a threat to human survival.In the environment,even if there is no pressure to choose,antibiotics can be retained for many years.Studies have confirmed that antibiotic-resistant bacteria can exist in the environment for a longer period of time than antibiotics,so the secondary pollution caused by antibiotics is more worthy of attention than the antibiotic itself to the water and soil environment.Conjugation is the main way of horizontal transfer of resistance genes and mutation is the way in which resistance genes are produced.Studies on the generation and transmission mechanisms of resistance genes help humans find ways to control the spread of resistance genes.Therefore,this article uses typical antibiotics:Sulfonamides（SAs）,Sulfonamide potentiators（SAPs）and Tetracyclines（TCs）as test compounds,Escherichia coli（E.coli）as the model organism.The effects of antibiotics on E.coli RP4 plasmid conjugation,mutation and growth inhibition were determined by individual or combined antibiotics and the mechanism was discussed.The main results are as follows:（1）The individual inhibition of typical antibiotics SAs,SAPs and TCs on E.coli growth and RP4 plasmid conjugation were studied:The effects of SAs,SAPs,and TCs on the growth inhibition of E.coli and RP4 plasmid conjugation both presented hormesis（low-dose promotion,high-dose inhibition）;dose-response curves of conjugation and growth inhibition can be divided into three cases according to their graphical characteristics.One is that the growth inhibition dose-response curve crosses the conjugation dose-response curve partially,such as SQ（one kind of SAs）and SAPs;the second is that growth inhibition dose-response curve is included in the conjugation dose-response curve and is in the right position,such as 5 SAs except SQ;the third is the growth inhibition dose-response curve is included in the conjugation dose-response curve and is in the left position,such as TCs.The linear regression results of the conjugation data and the physicochemical parameters and growth inhibition data of the compound were good,demonstrating the effect of the conjugation and the growth inhibition and the physicochemical properties of the drug itself（the logarithm of the dissociation constant p Ka and the octanol-water partition coefficient log P）are related;（2）The combined inhibition of typical antibiotics（SAs&TCs and SAs&SAPs） on E.coli RP4 plasmid conjugation was studied,and the relationship between the combined growth inhibition and conjugation was researched:The effect of the combination of SAs&TCs,SAs&SAPs on the RP4 plasmid conjugation presented hormesis.In this paper,the effect of combined antibiotic on RP4plasmid conjugation was discriminated,and the combined action was expressed by RU.The RU of RC_0-1（minimum concentration which promoted the conjugation）in the mixed system was RU₁,the RU of RC_0-2（the maximum concentration that promotes the conjugation）in the mixed system is RU₂.The results showed that RU₂s of SAs&SAPs were almost all synergistic,same with the combined toxicity;RU₁s of SAs&TCs were almost all antagonistic,also same with the combined toxicity.The linear regression of the conjugation data and the compound structural parameter E_bind（the binding energy of the compound to the target protein in bacteria）further proves that the combined action of conjugation is associated with combined toxicity.The active molar concentration of individual component in the mixed system bound to the target protein affects RC_0-1.Therefore,the joint use of antibiotics needs to be cautious;（3）The effects of individual SAs,indole,SAs+indole on sulfonamide resistance of E.coli were studied,and the effects of SAs on E.coli sulfonamide-resistant mutation and rifampicin（Rif）-resistant mutation were compared:SAs promoted the sulfonamide-resistant mutation in E.coli,and the greater the inhibition on bacterial growth,the greater the promotion of sulfonamide-resistant mutation.Control experiments with the addition of a certain concentration of quorum sensing signal molecules,indole,have shown that bacterial mutations are affected by bacterial quorum sensing,namely efflux pump.The overexpression of efflux pump genes can hinder the sulfonamide-resistant mutation to some extent;the most difference between sulfonamide-resistant mutation and Rif-resistant mutation of E.coli is the mutation frequency promotion rate,the former is bigger.We speculate that in the Rif screening mutation experiment,SAs can bind Sdi A at low concentration,stimulate the process of cell division,and inhibit the synthesis pathway of coenzyme F,resulting in more but low-quality cell division due to insufficient raw materials during the Rif screening process.In the SAs screening mutation experiment,the low concentration of SAs can be pumped out by the bacterial efflux pump system.When the SAs concentration is too large to exceed the capacity of the efflux pump,the growth of the bacteria is inhibited,thereby inducing bacteria to produce adaptive mutations.The main reason for the difference is that SAs is a bacteriostatic agent,and Rif is a bactericide.Although bacteriostatic agents are less toxic than bactericidal agents,it has greater potential to promote bacterial resistance mutations,making more serious resistance pollution.Through the above research,we have a more comprehensive understanding of the effects of individual or combined exposure of typical antibiotics on bacterial resistance.This paper discusses the bacterial resistance mechanism with antibiotic toxicity and bacterial quorum sensing.The research has laid a theoretical foundation of the study on the mechanism of bacterial resistance,provided new ideas,reference and support for the ecological risk assessment of antibiotics.