The Characteristics Of The First Case Of NDM-1-producing Enterobacter Cloacae Infection In China

Background: Carbapenems resistant bacteria gradually increasedwith the carbapenem antibiotics are widely used in clinic. Bacteriaproducing these β-lactamases may cause serious infections in which thecarbapenemase activity renders many β-lactams ineffective.Carbapenemases are members of the molecular class A, B, and Dβ-lactamases. Class A and D enzymes have a serine-based hydrolyticmechanism, while class B enzymes are metallo-β-lactamases that containzinc in the active site，They have the ability to hydrolyze penicillins,cephalosporins, monobactams, and carbapenems. The metallo-β-lactamasesbelong to the IMP、VIM、SPM-1、GIM-1、SIM-1、AIM-1、DIM-1、TMB-1、KHM-1and NDM-1families and have been detected primarily inPseudomonas aeruginosa，Enterobacteriaceae，Acinetobacter and so on.NDM-1-producing K. pneumoniae KP05-506and E.coli NF-NDM-1firstreported in2008, the resistant strains at an alarming rate spread all over theworld. NDM-1-producing bacteria have been reported in Europe, Asia,North and South America, Latin America and Australia. NDM-1-producing strains in Chinese mainland have been reported in Enterococcus,Acinetobacter baumannii, Klebsiella pneumoniae and Klebsiella ozaenae,and NDM-1-producing Enterobacter cloacae just found in India, has notbeen reported in Chinese mainland.Object: To investigate the prevalence of metallo-β-lactamase inEnterobacter cloacae isolated from our hospital during2007.1-2012.2, andfirst study the clinical characteristics, drug resistance and resistancemechanisms of the NDM-1-producing Enterobacter cloacae.Methods: All strains of Enterobacter cloacae were isolated from clinicalspecimens by routine method.The antimicrobial susceptibility wasevaluated by disc diffusion test(Kirby—Bauer) and agar dilution test．Themodified Hodge test and Etest MBL test were used to co-detectmetallo-β-lactamase. PCR were used to amplify MBLs genes. Conjugationtest was used to check the transfer of NDM-1-encoding plasmids. Thehomology of carrying blaNDM-1Enterobacter cloacae was detected by PFGE.Southern blotting located blaNDM-1gene.Results: A total of14carbapenm resistant strains were isolated, and theirphenotype confirmation tests showed6strains of producescarbapenmase.One strain of NDM-1-producing E. cloacae413isolatedfrom a67-year-old female patient with pneumonia in the sputum.In vitro, E.cloacae413was only sensitive to polymyxin B and fosfomycin. Thehomology of E. cloacae413was detected as B type by PFGE.The blaNDM-1 was carried on about20Kb in size plasmid.The plasmid also carryingmultiple resistance genes of blaCTX-M-14, qnrA, qnrS, aac6’-Ib-cr andrmtA.These resistant genes with the plasmid transfer between differentbacteria. So both conjugant E.coli J53(PNDM-1) and E. cloacae413wereresistance to carbapenem, quinolone and aminoglycoside antimicrobials.Conclusion:We first isolated NDM-1-producing Enterobacter cloacaein Chinese mainland.The resistant strain was resistance to carbapenem,quinolone and aminoglycoside antimicrobials,and this resitance can betransferred by plasmid. Reinforce the monitoring of the resistant bacteriaand rational uses of antimicrobial agents are of great significance.