Epidemiology Characteristics And Dissemination Mechanism Of IMP Type Metal Beta-Lactamase In Enterobacteriaceae Isolates

Objective:To understand the epidemiology characteris of IMP type metal beta-lactamase in Enterobacteriaceae isolates collected between August,2007and October,2011in Tongji hospital who are not susceptible to Carbapenems; In order to discover the dissemination characteristics of IMP gene, we analysed the integron structure of plasmid which carry IMP resistant gene.Methods:We screened out Enterobacteriaceae isolates which were not susceptible to meropenem and imipenem, the inhibition zone diameters of meropenem and imipenem were less than23mm, by K-B disk diffusion method. These strains were collected between August,2007and October,2011in Tongji hospital; IMP gene were detected by PCR, and the clinical data of IMP positive strains were analysed retrospectively; The minimal inhibitory concentration (MIC) of IMP positive strains were detected by agar dilution method, in order to get the drug susceptibility spectrum of IMP positive strain; Klebsiella pneumoniae and Escherichia coli strains which were IMP gene positive were tested by multilocus sequence typing (MLST) to analyse the holomogy; The transitivity of the plasmids which were carrying IMP resistant gene were detected by plasmid conjugation test, and the transconjugants were obtained. Then the structure of the plasmid carrying IMP gene were analysed by overlapping PCR to study the dissemination mechanism.Results:There were125Enterobacteriaceae isolates which were not susceptible to meropenem or imipenem from August,2007to October,2011in Tongji hospital; Klebsiella pneumoniae was the most common strain, followed by Enterobacter cloacae and Escherichia coli. We detected the IMP gene by PCR and got28IMP positive strains, account for22.4%(28/125). The clinical characteristics of the28positive strains were analysed,and the result showed that these strain were mainly isolated from pediatrics department(57.1%,16/28). Besides, they were mainly isolated from sputum (71.4%,20/28); Agar dilution susceptibility testing result showed that the susceptible rate of the28strains to amikacin and levofloxacin were both above70%, The susceptible rate of imipenem was71.4%, the susceptible rate of meropenem was32.1%; Multilocus sequence typing of Klebsiella pneumoniae and Escherichia coli showed a diversity of sequence types and4new sequence types (ST-734, ST-735, ST-736, ST-752) were found in13isolates of Klebsiella pneumoniae;9transconjugants which contain plasmid carrying IMP gene were acquired by conjugation test; Analying of integron structure, it showed that the IMP gene usually existed as individual gene cassette or followed after type I integrase.Conclusion:The detection rate of Enterobacteriaceae isolates be resistant to carbapenems show to be increase year by year, Klebsiella pneumoniae was the most common bacteria. IMP resistance gene usually spreaded as single gene cassette, and it was mostly often found in the first gene cassette of integron. Fluoroquinolone could be used as empirical treatment method to cure the infection caused by IMP type metal beta-lactamase positive strains.