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Antimicrobial Agents and Chemotherapy, February 2001, p. 447-453, Vol. 45, No. 2
0066-4804/01/$04.00+0   DOI: 10.1128/AAC.45.2.447-453.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

OXA-28, an Extended-Spectrum Variant of OXA-10 beta -Lactamase from Pseudomonas aeruginosa and Its Plasmid- and Integron-Located Gene

Laurent Poirel, Delphine Girlich, Thierry Naas, and Patrice Nordmann*

Service de Bactériologie-Virologie, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, 94275 Le Kremlin-Bicêtre, France

Received 14 February 2000/Returned for modification 13 June 2000/Accepted 28 October 2000

Pseudomonas aeruginosa ED-1, isolated from a pulmonary brush of a patient hospitalized in a suburb of Paris, France, was resistant to ceftazidime and of intermediate susceptibility to ureidopenicillins and to cefotaxime. Cloning and expression of the beta -lactamase gene content of this isolate in Escherichia coli DH10B identified a novel OXA-10 variant, OXA-28, with a pI value of 8.1 and a molecular mass of 29 kDa. It differed from OXA-10 by 10 amino acid changes and from OXA-13 and OXA-19 by 2 amino acid changes, including a glycine instead of tryptophan at position 164, which is likely involved in its resistance to ceftazidime. Like OXA-11, -14, -16, and -19 and as opposed to OXA-17, OXA-28 predominantly compromised ceftazidime and had only marginal effect on the MICs of aztreonam and cefotaxime in P. aeruginosa. Once expressed in E. coli, OXA-28 raised the MIC of ceftazidime to a much higher level than those of amoxicillin, cephalothin, and cefotaxime (128, 16, 8, and 4 µg/ml, respectively). OXA-28 beta -lactamase had a broad spectrum of activity, including ceftazidime. Its activity was partially antagonized by clavulanic acid (50% inhibitory concentration, 10 µM) and NaCl addition. The oxa28 gene cassette was inserted in the variable region of a class 1 integron, In57, immediately downstream of an amino 6'-N-acetyltransferase gene cassette, aac(6')Ib. The structures of the integrons carrying either oxa28, oxa13, or oxa19 gene cassettes were almost identical, suggesting that they may have derived from a common ancestor as a result of the common European origin of the P. aeruginosa isolates. In57 was located on a self-transferable plasmid of ca. 150 kb that was transferred from P. aeruginosa to P. aeruginosa.

* Corresponding author. Mailing address: Service de Bactériologie-Virologie, Hôpital de Bicêtre, 78 rue du Général Leclerc, 94275 Le Kremlin-Bicêtre Cedex, France. Phone: 33-1-45-21-36-32. Fax: 33-1-45-21-63-40. E-mail: nordmann.patrice{at}bct.ap-hop-paris.fr.

Antimicrobial Agents and Chemotherapy, February 2001, p. 447-453, Vol. 45, No. 2
0066-4804/01/$04.00+0   DOI: 10.1128/AAC.45.2.447-453.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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