Study On The Influence Of Antibiotics On The Growth And Resistance Of Escherichia Coli Under Mixed Carbon Source

Sub-inhibitory concentrations of antibiotics in the environment can induce the Hormetic effect of bacteria,accelerate the evolution and spread of bacterial resistance,and cause serious ecological and health risks.In the actual environment,the carbon catabolite repression（CCR）mechanism of bacteria under the coexistence of multiple carbon sources will change the metabolic state of bacteria,thus affecting their antibiotic sensitivity and drug resistance.Therefore,in this paper,Escherichia coli（E.coli）was used as the test organism,and Ciprofloxacin（CIP）and 2-Methyltetrahydrofuran-3-one（MTHF）were selected as the test compounds.The toxic effects,mutation,and RP4 plasmid conjugation of E.coli under single and combined stress of CIP and MTHF were determined and evaluated in a mixed carbon source system composed of different concentrations(0.00,0.50,1.00,1.75,2.50,and 3.00 g·L^-1)of typical carbon source glucose（Glc）and basic medium（MH medium and LB medium）.The results show that:1)The presence of the preferred carbon source Glc under mixed carbon source conditions triggered the CCR mechanism of E.coli and led to secondary growth of E.coli,which caused changes in the metabolic state of E.coli and affected its antibiotic sensitivity and resistance.2)Under the condition of a Glc+MH mixed carbon source,single and combined exposures of CIP and MTHF could induce the Hormetic effect of E.coli.The increase of Glc concentration in the culture system led to the enhanced growth promotion of E.coli by CIP,MTHF,and CIP+MTHF at low concentrations（the maximum promotion rates increased from 26%,8%,and 14%to 84%,39%,and 47%,respectively）,and the inhibitory effect on the growth of E.coli was weakened at high concentrations(the EC₅₀ values increased from 1.56E-07,4.54E-02,and 1.81E-02 mol·L^-1 to 4.35E-07,7.21E-02,and2.91E-02 mol·L^-1,respectively).The addition of Glc in the culture system reduced the toxicity of antibiotics to E.coli.3)Under the condition of a Glc+MH mixed carbon source,CIP and MTHF single and combined exposures can induce E.coli mutations.The mutation frequency promotion rates of CIP,MTHF,and CIP+MTHF increased with the increase in Glc concentration（from 84%,62%,and 68%to 154%,961%,and 1615%,respectively）.The addition of Glc to the culture system was beneficial to the resistance mutation of E.coli.4)Under the condition of a Glc+LB mixed carbon source,CIP and MTHF single and combined exposures can induce RP4 plasmid conjugation in E.coli.When the concentration of Glc was higher than 1.75 g·L^-1,the conjugation of E.coli was inhibited（conjugation frequency promotion rate<0%）.The addition of Glc reduced the risk of RP4 plasmid conjugation in E.coli.In summary,under the condition of mixed carbon sources,the increase in Glc concentration in the culture system can reduce the bacterial toxicity of antibiotics,increase the risk of bacterial resistance development,and decrease the risk of resistance spread.This study can provide a data basis for the ecological risk assessment of antibiotics under the coexistence of multiple carbon sources in the real environment.