Antimicrobial resistant mechanisms of carbapenem-resistant Enterobacteriaceae / 中华检验医学杂志

ABSTRACT

Objective To investigate the antimicrobial resistant mechanisms of carbapenemrcsistant Entcrobactcriaceae (CRE),construct monitoring system of acquired carbapenemase.Methods Totally 5604 clinical isolates of Enterobacteriaceae in Tongji Hospital were collected from January 2007 to June 2010,including 100 isolates of which zone diameters of meropenem were not larger than 21 mm.Antibiotic susceptibility was performed to select CRE.Then,carbapanemase gene and genetie structure screenings were perforomed by polymerase chain reaction (PCR).Pulsed-field gel electrophoresis (PFGE) and Southern blot were used to analyze the plasmids of CRE.Multilocus sequence typing (MLST) was used to determine the genotypes and homology of these isolates.In addition,out membrane proteins were examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis ( SDS-PAGE ).Results Eleven isolates of CRE were collected and confirmed,most of them were Klebsiella.spp.( 7/11 ).Susceptibility of antimicrobial agents indicated that all these strains resistant to most antimicrobials.The minimal inhibitory concentration (MIC) range of meropenem were 8 - 64 mg/L,imipenem were 4 - 64 mg/L,ertapenem were 4 - 64 mg/L.However,susceptibilities of aminoglycosides and fluoroquinoloncs were significantly different.PCR results showed that six isolates were blaIMP-4 positive and three isolates were blakPC.2 positive,including one isolate of K.pneumoniae (ST476) carrying both blaIMP-4 and blaKPC-2 genes.Genetic structure of carbapenemase genes were analyzed,suggesting that blaKPC-2 located in an integrated structure of a Tn3-based transposon and partial Tn4401 segment.PFGE showed that most CRE contained three or more plasmids.Two isolates of K.pneumoniae were assigned to the same sequence type,ST476,by MLST.SDS-PAGE indicated that only one isolate (Kox656) lacked two out membrane proteins ( OmpK35 and OmpK36 ).Conclusions The most common carbapenemase-resistant Enterobacteriaceae was K.pneumoniae in our hospital.Producing IMP-4 was the most common reason that bacteria resistant to carbapencms.The concomitant presence of these genes poses therapeutic as well as infection control problems.Attention should be payed to the characteristies of bacterial resistance and clinical epidemiology of drug-resistant infections in hospital,and thus to provide clinical reference.