The Epidemiology And Resistance Mechanisms Of Carbapenem-resistant Enterobacteriaceae In China

[Objective] To investigate the risk factor, clinical outcome, molecular epidemiology and resistance mechanism of carbapenem resistant Enterobacteriaceae (CRE).[Methods] Three hundred and fourty-two CREs from 34 hospitals in China from 2004-2012 were collected. Case-control study was carried out to analyze the risk fator and clinical outcome of CRE infections. Agar dilution method was conducted to determine minimum inhibitory concentrations (MICs) of antimicrobial agents. Modified Hodge Test was conducted to detect carbapenemases. The mobility of plasmids was confirmed by conjugation tests. Plamids were extracted and carbapenemase genes were located by Southern blot. The Whole plasmid sequencing was carried out to analyze genetic environment of carbapenemase genes. Beta-lactamase genes, including carbapenemase genes were detected by Polymerase chain reaction and sequencing. Outer membrane protein analysis was carried out by using SDS-PAGE. The clonal dissemination was detected by MLST and PFGE. The effect of marR mutation on carbapenem resistance was confirmed by gene clone technology.[Results] The treatment failure rate of CRE infections was 76.7%. "greater than 7 days of broad spectrum antibiotic use during 2 months before CRE infection" was the independent risk factor of CRE infection (OR=19.088, P=0.006). The antimicrobial agents with high activity included polymyxin B (96.1%), tigecycline (84.2%) and amikacin(55.5%).70.5%(241/342) of the CREs carried cabapenemase genes, including 173 carrying blaKPC-2,26 carying blaNDM-1 42 carrying blaIMP-type-The number of KPC-2-producing isolates arises during the recent 5 years and NDM-1-producing isolates emerged in 2010. Most of the KPC-2-producing CREs were located in Zhejiang Province, Beijng City and Jiangsu Province. MLST revealed that 69.1%(105/152) of the carbapenemase-producing K.pneumoniae were ST11, while 17 STs were distributed in the 29 carbapenemase-producing E.coli strains. Different carbapenemase genes were located in different plasmids. Whole plasmid sequencing showed that many mobile elements, including transposon, Insertion sequence and Integron, played important roles in carbapenem resistance. Outer membrane protein analysis showed that porin loss was the main resistance mechanism in carbapenemase-non-producing isolates. MarR mutation analysis revealed that MarR mutation of Gln42Arg can lead to MarR inactivation and then increase the resistance level to carbapenems.[Conclusions] This is a national multicenter,9-years study on CRE epidemiology and resistance mechanisms. It clarified CRE high treatment failure and risk factors. Molecular epidemiology revealed that carbapenemase-producing isolates were the major parts of CREs, and ST11 was the predominant ST type of carbapenem resistant K.pneumoniae. Carbapenemase-production and Porin loss played important role in resistance mechanisms. MarR mutation can also lead to carbapenem resistance in some CREs.