Prevalence Of Colistin-resistance Gene Mcr-1 In Enterobacteriaceae From Bloodstream Infections In Zhejiang Province

Objective:To investigate the prevalence of colistin-resistance and mcr-1 gene in Escherichia coli(E.coli)and Klebsiella pneumoniae(K.pneumoniae)from bloodstream infections in Zhejiang Province.Methods:A total of 869 clinical Enterobacteriaceae isolates,including 611 Escherichia coli(E.coli)?and 258 Klebsiella pneumoniae(K.pneumoniae)collected from patients with bloodstream infections(BSIs)in Zhejiang communities and hospitals from March 2014 to April 2015.The strains were screened for colistin resistance by broth microdilution method and for the presence of mcr-1 gene by PCR amplification.For mcr-1-positive isolates,other antibiotic susceptibilities were assessed and their molecular typing was performed using PFGE and ?MLST.The genetic location of mcr-1 was determined by analysis of PFGE profiles of S1-digested genomic DNA following Southern blot hybridization.Plasmid transfer to E.coli recipients was?investigated using filter mating or electroporation.The clinical data of the BSIs patients infected with ?mcr-1-positive isolates was collected and analyzed.SI-PFGE in combination with Southern hybridizations were used to locate the mcr-1 genes.The conjugation experiment confirmed the horizontal transfer of the mcr-1 gene.Results:All of the 869 Enterobacteriaceae isolates were tested for colistin susceptibility,of which the MIC values ranged from ?0.06 to 16?g/ml.A total of 6 E.coli isolates were identified to be colistin-resistant and mcr-1-positive,with the MIC values ranged from 8 to 16?g/mL,while no K.pneumoniae resistant to colistin or mcr-1 positive was identified.All mcr-1-positive isolates were susceptible to carbapenems and most of the isolates(83.33%,5/6)were susceptible to tigecycline and(3-lactamase inhibitor combinations tested.The 6 mcr-1-positive isolates carried mcr-1 on three types of different plasmids with the sizes of ca.33kb,61 kb and 244.4kb,respectively.The conjugation experiment showed that 3 of the 6 strains were able to conjugate successfully.Conclusions:The prevalence of the mcr-1 gene in E.coli and K.pneumoniae from BSIs was low in Zhejiang Province and showed low-level resistance to colistin.The mcr-1-positive isolates were usually non-pathogenic clones and remained susceptible to many antimicrobial agents,which led to favorable outcome.We suggest further studies should be conducted to clarify the clinical impact of this novel resistance gene to public health.