JAC Advance Access originally published online on February 4, 2008
Journal of Antimicrobial Chemotherapy 2008 61(3):498-503; doi:10.1093/jac/dkm538
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Original research |
Molecular characterization of AmpC-producing Escherichia coli clinical isolates recovered in a French hospital
1 Service de Bactériologie-Hygiène, Centre hospitalier universitaire d’Amiens, Hôpital Nord, Amiens, France 2 Service de Bactériologie-Virologie-Hygiène, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, Université Paris Sud, K.-Bicêtre, France
Received 6 July 2007; returned 28 November 2007; revised 23 September 2007; accepted 12 December 2007
* Correspondence address. Service de Bactériologie-Virologie, Hôpital de Bicêtre, 78 rue du Général Leclerc, 94275 Le Kremlin-Bicêtre Cedex, France. 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 AmpC-type β-lactamases produced by Escherichia coli clinical isolates.
Methods: E. coli isolates recovered in a French hospital in 2006 were selected on the basis of a resistance phenotype consistent with increased AmpC production. The presence of genes coding for plasmid-mediated cephalosporinases as well as the existence of mutations in the chromosome-borne ampC genes was studied by PCR and sequencing. Genes for chromosomal cephalosporinases were cloned and the conferred resistance patterns were analysed. The isolates were submitted to phylotyping and genotyping analysis.
Results: Thirty-four out of 2800 E. coli isolates were selected. Sixteen isolates, which overexpressed their chromosomal wild-type cephalosporinases due to mutations into their promoter sequence, were susceptible to extended-spectrum cephalosporins (ECLs). Eighteen isolates, mostly of the commensal phylogenetic group A or B1, had reduced susceptibility to ECLs, due to the production of chromosomal extended-spectrum AmpC (ESAC) β-lactamases, or plasmid-mediated cephalosporinases (CMY-2 and ACC-1), or to combined mechanisms of resistance. Sequence analysis showed that ESAC β-lactamases had amino acid changes in the R2 binding site, among which was a novel structural change corresponding to the duplication of Ile-283 in the H-9 helix. All the E. coli clinical isolates were non-clonally related except for four CMY-2-producing strains.
Conclusions: This work sheds new light on the spread of ESAC β-lactamases in E. coli. It showed that this emerging mechanism of resistance could be as frequent as plasmid-mediated cephalosporinases (0.21% and 0.28% of the E. coli isolates, respectively) and that a phenotypic approach is not able to identify these mechanisms of resistance.
Keywords: cephalosporins , ESAC , CMY , β-lactamase
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