title: Molecular characterization of a novel class 1 integron containing bla(GES-1) and a fused product of aac3-Ib/aac6'-Ib' gene cassettes in Pseudomonas aeruginosa.
abstract: 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 beta-lactamase (ESBL) with a pI of 5.8 that appeared to be chromosomally encoded. Cloning experiments revealed that this ESBL was encoded by bla(GES-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 beta-lactamase inhibitors and extended-spectrum cephalosporins was detected, in contrast to the resistance pattern observed in K. pneumoniae. Further sequence analysis demonstrated that the bla(GES-1) gene cassette was located in a class 1 integron, which contained another sequence corresponding to the fused aac3-Ib and aac6'-Ib' gene cassettes. The fusion product was functional, as was the product of each gene cloned separately: AAC3-I, despite the deletion of the four last amino acids, and AAC6', which carried three amino acid changes compared with the most homologous sequence. The AAC3-I protein conferred an expected gentamicin and fortimicin resistance, and the AAC6', 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 AAC6' activity with a higher level of gentamicin resistance without accompanying fortimicin resistance.
authors.affiliation: Laboratoire de Microbiologie, Faculté de Pharmacie, Université de Bordeaux 2, 33076 Bordeaux Cedex, France. veronique.dubois@bacterio.u-bordeaux2.fr
authors.forename: Véronique
authors.initials: V
authors.lastname: Dubois
authors.forename: Laurent
authors.initials: L
authors.lastname: Poirel
authors.forename: Caroline
authors.initials: C
authors.lastname: Marie
authors.forename: Corinne
authors.initials: C
authors.lastname: Arpin
authors.forename: Patrice
authors.initials: P
authors.lastname: Nordmann
authors.forename: Claudine
authors.initials: C
authors.lastname: Quentin
mesh_terms: D000123:Acetyltransferases / Q000235:genetics*; D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D003001:Cloning, Molecular; D003227:Conjugation, Genetic / Q000235:genetics; D004274:DNA, Recombinant / Q000096:biosynthesis / Q000235:genetics; D004351:Drug Resistance; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D010957:Plasmids / Q000235:genetics; D011550:Pseudomonas aeruginosa / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018440:beta-Lactam Resistance
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D004274:DNA, Recombinant; D000123:Acetyltransferases; C056532:aminoglycoside N(6')-acetyltransferase