The mechanism of carbapenems resistance in Serratia marcescens strains / 中华微生物学和免疫学杂志

ABSTRACT

Objective To investigate the mechanism of carbapenems resistance in Serratia marces-cens strains isolated from Wenzhou and their epidemiological characteristics.Methods 147 non-duplicated Serratia marcescens isolates were collected from the First Affiliated Hospital of Wenzhou Medical University during 2006 to 2012.The antimicrobial susceptibility test for all isolates was performed by using Vitek2 Compact to screen carbapenems-resistant Serratia marcescens strains.The minimum inhibitory concentrations ( MICs) of 10 commonly used antibiotics against carbapenems-resistant Serratia marcescens strains were de-termined by agar dilution method.The phenotypes of carbapenemase were analyzed by using the modified Hodge test.PCR analysis was used to detect the genes encoding carbapenemase, AmpC enzyme, efflux pump and outer membrane proteins.The changes of MICs before and after using CCCP efflux pump inhibitor were measured by agar dilution method.Outer membrane proteins were detected by SDS-PAGE.Carbapene-ms resistance genes were transferred from carbapenems-resistant Serratia marcescens strains to recipient strains by conjugation.The transconjugants were amplified by PCR and measured for MICs.Pulsed-field gel electrophoresis ( PFGE) was used to analyze homology among strains.Results 11 isolates resistant to car-bapenems were screened out from 147 Serratia marcescens isolates and all of them were resistant to penicil-lins, cephalosporins and ertapenem.10 out of the 11 isolates were both resistant to imipenem and meropen-em, but remained susceptible to fluoroquinolones and aminoglycoside.Among the 11 isolates, 10 carried blaKPC-2 gene, 1 carried blaIMP-1 gene, 8 harbored both blaEBC and blaMOX genes, 1 harbored both blaEBC and blaDHA genes, and 1 carried blaEBC , blaMOX and blaDHA genes.No additional genes were identified by PCR.The MICs of imipenem to 7 isolates and the MICs of ertapenem to 3 isolates were respectively decreased by 4-64 folds and 8-256 folds after using CCCP.CCCP had no effects on the MICs of meropenem.Loss of outer membrane protein was not detected among the 11 isolates.The blaKPC-2 genes were successfully transferred from 7 isolates into recipient strains.The MICs against the transconjugants were higher than those against the recipient strains in varying degrees.PFGE analysis demonstrated that 8 out of 11 Serratia marcescens strains belonged to one clonotype.Conclusion KPC-2 carbapenemase played an essential role in carbapenems re-sistance in Serratia marcescens strains isolated from Wenzhou.Attention should be paid to the clonal spread of KPC-2 and its horizontal transmission in Wenzhou.