JAC Advance Access originally published online on February 20, 2008
Journal of Antimicrobial Chemotherapy 2008 61(5):1020-1023; doi:10.1093/jac/dkn049
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Original research |
Characterization of carbapenem-non-susceptible Escherichia coli isolates from a university hospital in Taiwan
1 Institute of Basic Medical Sciences, College of Medicine, National Cheng-Kung University, Tainan, Taiwan 2 Department of Pathology, College of Medicine, National Cheng-Kung University, Tainan, Taiwan 3 Department of Internal Medicine, College of Medicine, National Cheng-Kung University, Tainan, Taiwan 4 Department of Medical Laboratory Science and Biotechnology, College of Medicine, National Cheng-Kung University, Tainan, Taiwan
Received 5 November 2007; returned 28 November 2007; revised 21 January 2008; accepted 22 January 2008
* Correspondence address. Department of Medical Laboratory Science and Biotechnology, College of Medicine, National Cheng-Kung University, No. 1 University Road, Tainan 70101, Taiwan. Tel: +886-6-2353535, ext. 5775; Fax: +886-6-2363956; E-mail: jjwu{at}mail.ncku.edu.tw
Objectives: To investigate characteristics of nine carbapenem-non-susceptible (CP-NS) Escherichia coli isolates collected between 1999 and 2005 at a Taiwanese university hospital.
Methods: Genetic relatedness was analysed by PFGE. β-Lactamases were characterized by PCR and isoelectric focusing. Outer membrane proteins and transcripts were investigated by SDS–PAGE and northern blotting. Cloning experiments were performed to investigate the role of membrane permeability in carbapenem non-susceptibility.
Results: The nine CP-NS isolates were found to produce the CMY-2 AmpC enzyme (n = 8), the CTX-M-14-type extended-spectrum β-lactamase (ESBL) (n = 1), the SHV-12 ESBL (n = 1) and the IMP-8-type metallo-β-lactamase (n = 1) alone or in combination. All CP-NS isolates revealed a decrease in the transcription and protein expression of ompC, and susceptibility to carbapenems was restored in one isolate by introducing the cloned ompC gene. PFGE revealed genetic diversity among the nine isolates. All patients with the CP-NS isolates had been treated with carbapenems (six patients) and/or extended-spectrum cephalosporins (five patients) before isolation.
Conclusions: Our study suggests that the decreased susceptibility to carbapenems in E. coli in the hospital might arise by the stepwise accumulations of multiple drug-resistance determinants in different clones.
Keywords: outer membrane proteins , ompC , β-lactamases
These authors contributed equally to this work.
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