Mechanism of metal ions against capturing drug resistance gene cassette by bacterial integron

Abstract:

[Objective] To explore the effect of metal ions against capturing drug resistance gene cassette by integron and the related mechanism.[Methods] An in vivo model of class 1 integron capturing resistance gene cassette was constructed in Escherichia coli.Different concentration of silver ions (0.3,0.9,and 1.5 μg/mL of Ag⁺) and copper ions (5,50,100,150,and 210 μg/mL of Cu²⁺) were used to intervene in the experimental group.The integration frequency of the experimental group and the control group was determined by real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) and validated by phenotypic screening.The concentration of metal ions absorbed by bacteria was measured by mass spectrometry,and the molecular mechanism of silver ion against capturing drug resistance gene cassette by bacterial integron was further analyzed by transcriptome sequencing.[Results] The integration frequencies were 9.42×10^‒5(6.49×10^‒5,1.44×10^‒4) in the 0.9 μg/mL silver ion group and 7.29×10^‒5(4.45×10^‒5,9.03×10^‒5) in the 1.5 μg/mL silver ion group,which were lower the 2.59×10^‒4(2.24×10^‒4,3.33×10^‒4) in the control group (P<0.001).In contrast,there was no significant difference between the groups with different concentration of copper ions and the control group.The gene expression level of E.coli before and after silver ion treatment was compared and analyzed by transcriptome sequencing.The differentially expressed genes were related to the Gene Ontology (GO) terms of methylgalactoside transport,maltose transport,phosphoenolpyruvate-glycerone phosphotransferase activity,and glycerone kinase activity,and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of amino sugar and nucleotide sugar metabolism,flagellum assembly,cationic antimicrobial peptide (CAMP) resistance,fructose and mannose metabolism,and phosphotransferase system (PTS).The top 12 hub genes (ptsG,malE,lamB,lacZ,malK,basR,ais,ugd,nagE,metN,malQ and malF) were screened out by protein-protein interaction (PPI) network.[Conclusion] A certain concentration of silver ions inhibited the integration of drug resistance gene cassettes by integron,while the effect of copper ions was not obvious.Therefore,not all metal ions with bactericidal properties had the effect on integration frequency.The mechanism of silver ions against capturing drug resistance gene cassette by bacterial integron was possibly through maltose transport and carbon catabolism.However,the processes of carbon catabolism and maltose transport were complex and deserved further study.At present,there is no related study on bacterial integron transcriptome.This study provides a new way to solve the problem of bacterial drug resistance.