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JAC Advance Access published online on June 22, 2007
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkm227
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© The Author 2007. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Extension of the hydrolysis spectrum of AmpC ß-lactamase of Escherichia coli due to amino acid insertion in the H-10 helix

Hedi Mammeri{dagger}, Laurent Poirel and Patrice Nordmann*

Service de Bactériologie-Virologie, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, Université Paris Sud, 94275 K.-Bicêtre, France

Received 28 December 2006; returned 22 February 2007; revised 2 May 2007; accepted 30 May 2007

* Corresponding author. Tel: +33-1-45-21-36-32; Fax: +33-1-45-21-63-40; E-mail: nordmann.patrice{at}bct.aphp.fr

Objectives: To characterize the naturally occurring expanded-spectrum ß-lactamase from an Escherichia coli clinical isolate and to compare it with a wild-type ß-lactamase.

Methods: The chromosome-borne ampC genes from E. coli BER and E. coli EC2 were PCR amplified, sequenced and cloned into an expression vector. Antimicrobial susceptibilities of the parental isolate and the recombinant strains were determined by agar dilution methods. Kinetic parameters were determined from purified AmpC BER and AmpC EC2.

Results: AmpC BER was overexpressed in its original clinical isolate because of mutations in the promoter region of its gene at positions –42 and –18. The analysis of the ampC coding sequence revealed a 6 bp insertion when compared with the wild-type sequence leading to the tandem duplication of two alanine residues inside the H-10 helix. AmpC BER-producing recombinants were resistant to ceftazidime, had reduced susceptibility to other oxyiminocephalosporins (cefotaxime and cefepime), but had a greater susceptibility to cefoxitin when compared with the recombinant expressing the wild-type ß-lactamase AmpC EC2. The affinity of AmpC BER for cephalosporins and imipenem was increased, whereas the hydrolysis rate was decreased for all these compounds. In addition, the IC50 values of clavulanic acid and tazobactam for AmpC BER were increased.

Conclusions: This work sheds new light on structure–function relationships of expanded-spectrum AmpC ß-lactamases.

Key Words: expanded-spectrum AmpC , cefepime , E. coli

{dagger} Present address. Service de Bactériologie-Hygiène, Centre Hospitalier Universitaire d'Amiens, Hôpital, Nord, 2 Place Victor Pauchet, 80080 Amiens, France.


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