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Antimicrobial Agents and Chemotherapy, November 2008, p. 3898-3904, Vol. 52, No. 11
0066-4804/08/$08.00+0 doi:10.1128/AAC.00403-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Service de Bactériologie-Virologie, INSERM U914: Emerging Resistance to Antibiotics, Hôpital de Bicêtre, Assistance Publique-Hôpitaux de Paris, Faculté de Médecine, Université Paris-Sud, Paris, France,1 Laboratoire de Bactériologie, Cliniques Universitaires Mont-Godinne,2 Laboratoire de Bactériologie, Clinique Universitaire Saint-Luc, Université Catholique de Louvain, Louvain, Belgium3
Received 25 March 2008/ Returned for modification 28 May 2008/ Accepted 18 July 2008
The genetic environment of the blaOXA-18 gene encoding a peculiar clavulanic acid-inhibitable Ambler class D extended-spectrum β-lactamase was determined from the prototype OXA-18-producing Pseudomonas aeruginosa MUS clinical isolate. An 8.2-kb genomic DNA fragment containing blaOXA-18 was cloned from P. aeruginosa MUS. Although most oxacillinases are located in integrons, blaOXA-18 lacked gene cassette-specific features. It was bracketed by two duplicated sequences containing ISCR19, a novel insertion sequence of the ISCR family of mobile elements;
intI1, a truncated integrase gene; and a truncated
aac6'-Ib gene cassette. It is likely that ISCR19 was at the origin of the blaOXA-18 gene mobilization by a rolling-circle transposition event followed by homologous recombination. Furthermore, analysis of the cloned genomic DNA fragment revealed the presence of the integron-containing blaOXA-20 gene. Concomitantly, three P. aeruginosa clinical isolates, displaying a synergy image as determined by double-disk diffusion tests on cloxacillin-containing plates, were isolated from three patients hospitalized in different wards over a 9-month period at the Saint-Luc University hospital (Brussels, Belgium). These isolates were positive by PCR for blaOXA-18 and blaOXA-20 genes, genetically related to P. aeruginosa MUS as determined by pulsed-field gel electrophoresis, and carried the same blaOXA-18/blaOXA-20-associated genetic structures. This report characterized the genetic elements likely at the origin of blaOXA-18 gene mobilization in P. aeruginosa and suggests the spread of oxacillin-type extended-spectrum β-lactamases in P. aeruginosa at the Saint-Luc University hospital of Brussels, Belgium.
Published ahead of print on 28 July 2008.
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