Epidemiological Investigation And Molecular Characteristics Of Colistin-resistance Gene Mcr-1 In Escherichia Coli

Objective Escherichia coli is an important and common conditional pathogen,and the clinical isolation rate is also getting higher and higher.According to the results of the Chinese Bacterial Resistance Surveillance Network(CHINET),Escherichia coli isolated from hospitals in China is steadily increasing,the carbapenem-resistant strains are also increasing year by year.Therefore,the drug resistance of Escherichia coli has received increasing attention.Colistin is clinically important for the treatment of multi-drug resistant bacteria and is considered to be one of the most effective treatments.It has been found that the mcr-1 gene causes bacteria to be resistant to colistin and was widely spread by plasmids.Therefore,understanding the resistance and transmission mechanism of mcr-1 resistance genes is of great significance for the study and monitoring of the prevalence rate of colistin resistance.Through the collection of non-repetitive Escherichia coli isolated from our hospital,homology analysis,drug sensitivity test,mcr-1 screening,etc,to understand the epidemiological situation and bacterial resistance of mcr-1 in our hospita and reference for monitoring colistin resistance and mcr-1 prevalence.Methods The clinical isolates of Escherichia coli from our hospital from 2015 to 2016 were collected.The mcr-1 gene was screened by polymerase chain reaction(PCR).For the positive strain of mcr-1,the paper diffusion method was used for drug sensitivity test,pulse field gel electrophoresis(PFGE)was used to verify homology.Localization of mcr-1 gene by S1-PFGE combined with Southern blot hybridization.Bacteria lconjugation experimen assay to verify horizontal transfer of mcr-1 gene.Clinical cases of the positive strain were collected.Results From 2015 to 2016,a total of 1112 strains of Escherichia coli were isolated,among them,there are six mcr-1 positive strains.The results of drug sensitivity test showed that all six strains of Escherichia coli were sensitive to imipenem and meropenem,among which five strains were sensitive to tegacycline and one strain was between sensitive and resistant.All strains were resistant to cefotaxime and cefepime.Six strains of mcr-1 positive Escherichia coli were divided into six different clonotypes.DNA hybridization results showed that the mcr-1 genes of the positive strains were located in plasmids.The conjugation experiment showed that all the 6 strains were able to conjugate successfully.All patients were treated with antibiotics and discharged from hospital.Conclusion The results showed that the prevalence of mcr-1 resistance gene in our hospital was at a low level of only 0.5%(6/1112),and the strain carrying the mcr-1 gene showed low levels of resistance to colistin.Other types of antibiotics are sensitive and have no effect on patient prognosis.Homology analysis showed that 6 strains of Escherichia coli belonged to 6 different clonotypes,indicating that there was no clonal transmission and it was epidemic.The mcr-1 resistance gene can coexist with other drug resistance genes,and whether the interaction between the two remains to be further studied.