Molecular types of carbapenem-non-susceptible Escherichia coli isolates and their mechanism of drug resistance / 中华微生物学和免疫学杂志

ABSTRACT

Objective To investigate the molecular types of carbapenem-non-susceptible Esche-richia coli ( E.coli) isolates and their mechanism of carbapenem resistance .Methods Twenty-two carbap-enem-non-susceptible E.coli strains were isolated from 3 hospitals in Hangzhou from 2007 to 2011.The mini-mum inhibitory concentrations ( MICs) of antimicrobials to those isolates were determined by agar dilution method and E-test.The molecular mechanisms of carbapenem resistance of E.coli isolates were analyzed by conjugation experiment,PCR and DNA sequencing.Pulsed-field gel electrophoresis (PFGE),multilocus se-quence typing ( MLST ) , and phylogenetic typing were performed to analyze the molecular epidemiology of those isolates.Results The MICs of imipenem and meropenem to 22 E.coli isolates were ranged from 1 μg/ml to 16 μg/ml,and the MICs of ertapenem were 2 μg/ml to 64 μg/ml.All E.coli isolates produced the KPC-2 carbapenemase and various β-lactamases , and some of them also produced plasmid-mediated AmpC enzymes.Carbapenem resistance was transferred by conjugation and transformation from 22 E.coli iso-lates to E.coli EC600 strains.The E.coli transconjugants or transformants acquired the blaKPC-2 gene and showed similar antibiotic susceptibility patterns in comparison with donor strains .Only a few isolates were in-distinguishable or closely related as indicated by PFGE .Four sequence types including ST131 (9 isolates), ST648 (5 isolates),ST38 (2 isolates) and ST405 (2 isolates) were identified by MLST.Phylogenetic analy-sis indicated that 9 ST131 isolates belonged to phylogenetic group B 2 and the other isolates belonged to group D (11 isolates),group B1 (1 isolate) and group A (1 isolate),respectively.Conclusion The sequence type of prevalent E.coli isolates producing KPC-2 from Hangzhou was ST131,which is an international epi-demic,multidrug-resistant clone,followed by ST648.