Studies On The Effects Of Antibiotics On Conjugative Transfer Of Resistant Plasmid Based On Quorum-sensing Signaling Molecules

Antibiotics are double-edged swords promoting the enrichment of antibiotic resistance genes(ARGs),an emerging pollutant in the environment as well as raising up the levels of medicare and husbandry development.In this dissertation the effects of different antibiotics,quorum sensing(QS)signal molecules and quorum-sensing inhibitors(QSIs)on the conjugative transfer of plasmid RP4 were investigated.Furthermore,the synergistic effects of tetracycline(TH)mixed with QS signal molecules or QSIs on the conjugative transfer of plasmid RP4 were evaluated.This study would play an important role in guiding the ecological risk assessment of antibiotics,complementing the dissemination mechanism of ARGs,and providing a theoretical basis to control the dissemination ofARGs.Firstly,the recipient strain MG1655 Nal was conjugated with strain MG1655(R388)and strain MG1655(RP4),respectively.According to the experimental results,MG1655(RP4)was chosen as the donor strain in the model of horizontal transfer of ARGs.The conjugation conditions were optimized after the univariate analysis:both the donor and recipient strains were resting in liquid LBmedium(pH7.0)at 37℃ for 8 hours.Secondly,the postantibiotic sub-MIC effects onconjugative transfer of plasmid RP4 were studied and the results were as follows:Sulfonamides(SAs)and Trimethoprim(TMP)could inhibit the conjugative transfer of RP4,while Tetracyclines(TCs)and Kanamycin(Km)could boost this transfer with a promoting rate that appeared to increase at first and decrease afterwards.Ampicillin(Amp)showed little impact on the transfer in our experiments.With respect to the dissemination of ARGs via horizontal gene transfer mediated by plasmid RP4,SAs,TMP and Amp revealed no ecological risk.By contrast,TCs and Km exhibited prominent ecological risks due to its promotion of the horizontal transfer of ARGs,therefore,their emission levels to the environment should be monitored.Thirdly,the effects of C6,C8(two QS signaling molecules)and R3P(a QSI)on the conjugative transfer of plasmid RP4 were investigated.In addition,the synergistic effects of TH mixed with these three drugs on the transfer of RP4 were studied,respectively.It was found that R3P of sub-MIC could inhibit the conjugative transfer of RP4,while C6 and C8 had no significant effect on it.In the case of conjugative transfer of RP4 promoted by TH,low concentration of C8 had a remarkable potentiation effect while C8 in high concentration or C6 showed an attenuation effect.R3P could attenuate the potentiation of RP4 conjugative transfer by TH,and the inhibition became more and more obvious with the incrasing concentration.Combined with the achievements of other researchers,the results in this work raised a presumed mode of the effect of antibiotics and QS system on the dissemination of ARGs via the conjugative transfer of plasmid RP4.