Analysis of carbapenemase genotypes of carbapenem-resistant Proteus mirabilis strains clinically isolated from 2009 to 2012
Objective To investigate the clinical distribution and the drug resistance of carbapenemresistant Proteus mirabilis strains isolated from 2009 to 2012 ; and to study carbapenemase genotypes of the isolates.Methods A total of 15 non-repetitive carbapenem-resistant Proteus mirabilis strains were selected from 422 Proteus mirabilis strains isolated from Ningbo First Hospital during January 2009 to December 2012.The minimal inhibitory concentrations (MIC) of 6 antibacterial agents,including imipenem (IPM),meropenem (MEM),ertapenem (ETP),ciprofloxacin (CIP),amikacin (AK) and minocycline (MIN),against 15 isolates were determined by E-test.The modified Hodge test (MHT) was used to detect the carbapenemase production in isolates.The PCR assay was performed to detect drug resistance genes of blaKPC,blaNDM-1,blaGES,blaSME,blaIMI-1/NmcA and blaSHV-38.Plasmids were extracted from the blaKPC-positive strains and then transformed into Escherichia coli J53 strains by electroporation.The transformed and untransformed Escherichia coli J53 strains were tested for MIC values and blaKPC gene by E-test and PCR respectively.Results The resistance rates of the 15 carbapenem-resistant Proteus mirabilis strains to IPM,MEM,ETP,CIP,AK and MIN were 100％,100％,100％,86.7％ (13/15),33.3％ (5/15) and 80％ (12/15),respectively.7 out of 15 strains were Hodge test positive,and 11 strains were blaKPC-2 positive.Results of PCR amplification showed that the transformed Escherichia coli J53 strains,whose MIC values to IPM,MEM,and ETP were increased by 2 to 64 times,were blaKPC-2 gene positive.Conclusion The carbapenem-resistant Proteus mirabilis strains in this study were resistant to many commonly used antibiotics,however,the resistance rates to AK were relatively low.The dominant carbapenemase genotype was blaKPC-2 carried by the plasmid.Attention should be paid to its easily transmissible feature among the strains in clinic. 
 
Key words: 
Proteus mirabilis;  blaKPC ;  PCR;  Plasmid;  Electroporation