ABSTRACT
Objeetive To explore the mechanism of drug resistance of New Delhi metallo-β-lactamase-1 (NDM-1) producing Enterobacteriaceae,and to investigate the characteristics of blaNDM-1 carrying plasmid and its gene environment.Methods A total of 48 strains of carbapenem-resistant Enterobacteriaceae were successively collected from six general hospitals in south China during August 2011 and January 2013.Escherichia coli J53 was used for plasmid conjugation.Modified Hodge test was performed,and PCR method was used for the detection of carbarpenase-related genes.The relative molecular mass of the blaNDM-1 carrying plasmid was determined using pulsed field gel electrophoresis (PFGE)assay,and enzyme digestion was performed to investigate the homology and incompatibility group of the plasmid.Clinical feature of blaNDM-1 producing Enterobacteriaceae infection was also investigated.Results Among 48 strains of carbapenem-resistant Enterobacteriaceae,43 were positive in modified Hodge tests.blaVIM,blaGIM and blaSPM genes were negative in all strains,while blaNDM-1 was positive in 19 strains including 3 strains of Escherichia coli,5 strains of Klebsiella pneumoniae,6 strains of Enterobacter cloacae,3 strains of Citrobacterfreundii,1 strain of Klebsiella oxytoca and 1 strain of Providencia rettgeri.All the 19 strains were resistant to imipenem,cefotaxime,ceftazidime,cefepime,aztreonam and piperacillin/tazobactam,47.3％ strains were resistant to ciprofloxacin and levofloxacin,but 68.4％ strains were sensitive to amikacin.Conjugation experiment showed that,blaNDM-1 carrying plasmids in 13 strains were transmitted to the Escherichia coli J53.The conjugants were resistant to imipenem,ceftazidime,cefotaxime and piperacillin/tazobactam,but were sensitive to amikacin,ciprofloxacin and levofloxacin.All genes in conjugant J-FR90 (Providencia rettgeri) were negative,while the remaining 12 conjugants carried blaNDM-1,blaSHV and aac-(6')-Ib genes.PFGE showed that,the sizes of all blaNDM-1 carrying plasmids were about 50 kb,and more than 80％ of their macrorestriction maps were similar.The plasmid belonged to incompatibility group IncX3,and exhibited 100％ passage stability after 500 generations of propagation.Among 19 patients infected with NDM-1 producing Enterobacteriaceae,6 died and 13 survived.Conclusions NDM-1 producing Enterobacteriaceae is emerging in south China,and blaNDM-1 is transmitted to Enterobacteriaceae through IncX3.Patients infected with NDM-1 producing Enterobacteriaceae usually have good prognosis.