The Analysis Of Resistance Mechanism And Homogeneity Of VIM-2 Metallo-β-lactamase Producing Acinetobacter Baumannii

Objective:To explore the drug resistance of VIM-2 metallo-β-lactamase producing Acinetobacter baumannii isolated from patients of The First Affiliated Hospital Of Nanchang University,and to analyze the underlying mechanism and their homogeneity.Methods:400 pandrug-resistant Acinetobacter baumannii（PDR-AB）strains were clinically isolated from the First Affiliated Hospitalof Nanchang University during the period from 2011 to 2014.VITEK2 compact automatic instrument and its accessory were used to identify and analyze 15 antimicrobial resistance including Piperacillin,Aztreonam and so on.Modified Hodge test was applied to detect the expression of carbapenemase;EDTA experiment was applied to detect the expression ofMBL;PCRamplification assay and DNA sequencing were employed to detect the resistance related genes such as bla _VIM,bla_NDM bla_KPC,bla_OXA-40,I-CLASS intergongene,variable region and CarO gene;To analyze the alteration of outer membrane protein components,SDS^PAGE analysis was performed;ERIC–PCR assay was used to study both the genotyping of strains and the source and resistant genes of the strains with the same spectrum types.Results:Among the 400 isolates,33.07%and 48.19%are resistant to Levofloxacin and compound sulfamethoxazole,respectively.Of the other 13 kinds of antibiotic,the resistant rates were ranged from 77.30%to 95.18%.Modified Hodge test demonstrated that carbapenemase was expressed in all the 240 carbapenem-resistant Acinetobacter baumannii,EDTA experiment prove that 80strains Acinetobacter baumannii produce MBL.Among the 240 resistant strains,18 harbored bla _VIM-2IM-2 gene,respectively,16 harbored bla _NDM gene,133 harbored bla _TEM-1,195 harbored bla_OXA-23,188 harbored bla_armA;55.42%,81.25%and 78.33%isolates carried bla_TEM-2,bla_OXA-23 and bla_armA;Among18 harbored blaVIM-2 gene,all were identified Int1 linking to bla_VIM-2 gene;9（50%）lacked the CarO gene（9/18）,as indicated by PCR amplification assay and DNA sequencing.SDS-PAGE analysis further proved that the expression of outer membrane protein CarO of VIM-AB was lowered or missed.and other resistance genes were not discovered.ERIC–PCR gene mapping showed that there are mainly six kinds of genotypes in this VIM-AB 18 strains,including 6 strains of type A and 4 strains of type B,3strains of type C,2 strains of type D,2 strains of type E,1strains of type F.Conclusions:the resistance mechanism of PDR-AB to carbapenems is mainly mediated by bla_TEM-1,bla_OXA-23XA-23 and bla_armA;meanwhile,VIM-2,NDM metallo-β-lactamase and lack or change of outer membrane protein are attributable to carbapenem resistance of clinically isolated PDR-AB in the First Affiliated Hospitalof Nanchang University,and the class1 integron plays an role in mediating bla_VIM-2 gene transmission.