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Antimicrobial Agents and Chemotherapy, March 2002, p. 638-645, Vol. 46, No. 3
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.3.638-645.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Molecular Characterization of a Novel Class 1 Integron Containing blaGES-1 and a Fused Product of aac(3)-Ib/aac(6")-Ib" Gene Cassettes in Pseudomonas aeruginosa

Véronique Dubois,1* Laurent Poirel,2 Caroline Marie,3 Corinne Arpin,1 Patrice Nordmann,2 and Claudine Quentin1

Laboratoire de Microbiologie, Faculté de Pharmacie, Université de Bordeaux 2,1 Laboratoire de Bactériologie, Hôpital Pellegrin, Bordeaux,3 Service de Bactériologie-Virologie, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, Le Kremlin-Bicêtre, France2

Received 9 April 2001/ Returned for modification 29 July 2001/ Accepted 23 November 2001

As seen by the disk diffusion method, the clinical strain of Pseudomonas aeruginosa Pa695, resistant to all extended-spectrum cephalosporins and aminoglycosides, exhibited an unusual synergistic effect between ceftazidime and imipenem. This isolate produced an extended-spectrum ß-lactamase (ESBL) with a pI of 5.8 that appeared to be chromosomally encoded. Cloning experiments revealed that this ESBL was encoded by blaGES-1, previously described in an integron from Klebsiella pneumoniae. In P. aeruginosa Pa695, a higher level of resistance to ceftazidime than to ticarcillin was observed, and no synergy between the ß-lactamase inhibitors and extended-spectrum cephalosporins was detected, in contrast to the resistance pattern observed in K. pneumoniae. Further sequence analysis demonstrated that the blaGES-1 gene cassette was located in a class 1 integron, which contained another sequence corresponding to the fused aac(3)-Ib and aac(6")-Ib" gene cassettes. The fusion product was functional, as was the product of each gene cloned separately: AAC(3)-I, despite the deletion of the four last amino acids, and AAC(6"), which carried three amino acid changes compared with the most homologous sequence. The AAC(3)-I protein conferred an expected gentamicin and fortimicin resistance, and the AAC(6"), despite the Leu-119->Ser substitution, yielded resistance to kanamycin, tobramycin, and dibekacin, but slightly affected netilmicin and amikacin, and had no apparent effect on gentamicin. The fusion product conveyed a large profile of resistance, combining the AAC(6") activity with a higher level of gentamicin resistance without accompanying fortimicin resistance.


* Corresponding author. Mailing address: Laboratoire de Microbiologie, Faculté de Pharmacie, Université de Bordeaux 2, 146 rue Léo Saignat, 33076 Bordeaux Cedex, France. Phone: 33 5 57 57 10 75. Fax: 33 5 56 90 90 72. E-mail: veronique.dubois{at}bacterio.u-bordeaux2.fr.


Antimicrobial Agents and Chemotherapy, March 2002, p. 638-645, Vol. 46, No. 3
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.3.638-645.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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