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Journal of Clinical Microbiology, March 2008, p. 1037-1044, Vol. 46, No. 3
0095-1137/08/$08.00+0     doi:10.1128/JCM.00197-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Successive Emergence of Extended-Spectrum β-Lactamase-Producing and Carbapenemase-Producing Enterobacter aerogenes Isolates in a University Hospital{triangledown}

M. Biendo,1* B. Canarelli,1 D. Thomas,1,2 F. Rousseau,1 F. Hamdad,1 C. Adjide,1 G. Laurans,1,2 and F. Eb1,2

Service de Bactériologie et d'Hygiène CHU NORD, Place Victor Pauchet, 80054 Amiens, Cedex 1 France,1 Laboratoire de Bactériologie, Faculté de Médecine, 80036 Amiens, Cedex France2

Received 26 January 2007/ Returned for modification 3 March 2007/ Accepted 15 January 2008

Sixty-two clinical isolates of Enterobacter aerogenes resistant to expanded-spectrum cephalosporins were collected between July 2003 and May 2005. Among these isolates, 23 (37.1%) were imipenem (IPM) susceptible, and 39 (62.9%) were IPM insusceptible, of which 89.7% (35/39) were resistant and 10.3% (4/39) were intermediate. Isolate genotypes were compared by pulsed-field gel electrophoresis. Of 62 isolates, 48 belonged to epidemic pulsotype A (77.4%). This pulsotype included 37.5% and 58.4% of β-lactam phenotypes b and a, respectively. Nine isolates (14.5%) belonged to pulsotype E, which included 22.3% and 77.7% of phenotypes b and a, respectively. The β-lactamases with pIs of 5.4, 6.5, 8.2, and 8.2 corresponded to extended-spectrum β-lactamases (ESBLs) TEM-20, TEM-24, SHV-5, and SHV-12, respectively. Of 39 IPM-insusceptible E. aerogenes isolates, 26 (66.6%) were determined to be metallo-β-lactamase producers, by using a phenotypic method. Of these isolates, 24 harbored a blaIMP-1 gene encoding a protein with a pI of >9.5, and two carried the blaVIM-2 gene encoding a protein with a pI of 5.3, corresponding to β-lactamases IMP-1 and VIM-2, respectively. The remaining 13 (33.4%) isolates were negative for the blaIMP-1 and blaVIM-2 genes but showed an alteration of their outer membrane proteins (OMPs). Ten of these isolates produced the two possible OMPs (32 and 42 kDa), with IPM MICs between 8 and 32 µg/ml, and three others produced only a 32-kDa OMP with IPM MICs >32 µg/ml. This work demonstrates that, in addition to resistance to expanded-spectrum cephalosporins, IPM resistance can occur in ESBL-producing E. aerogenes isolates by carbapenemase production or by the loss of porin in the outer membrane.

* Corresponding author. Mailing address: Laboratoire de Bactériologie-Hygiène, CHU Nord—Place Victor Pauchet—80054 Amiens, Cedex 1, France. Phone: 03 22 66 84 30. Fax: 03 22 66 84 98. E-mail: Biendo.Maurice{at}chu-amiens.fr

{triangledown} Published ahead of print on 30 January 2008.

Journal of Clinical Microbiology, March 2008, p. 1037-1044, Vol. 46, No. 3
0095-1137/08/$08.00+0     doi:10.1128/JCM.00197-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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