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Antimicrobial Agents and Chemotherapy, August 1998, p. 2074-2083, Vol. 42, No. 8
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Molecular Characterization of OXA-20, a Novel Class D beta -Lactamase, and Its Integron from Pseudomonas aeruginosa

Thierry Naas,1,* Wladimir Sougakoff,2 Anne Casetta,3 and Patrice Nordmann1,3

Service de Bactériologie-Virologie, Hôpital Antoine Béclère, Faculté de Médecine Paris-Sud, 92141 Clamart Cedex,1 Service de Bactériologie-Hygiène, Faculté de Médecine Pitié-Salpêtrière, 75634 Paris Cedex 13,2 and Service de Bactériologie-Virologie, Hôpital de Bicêtre, Faculté de Médecine Paris-Sud, 94274 Le Kremlin-Bicêtre,3 France

Received 3 December 1997/Returned for modification 3 March 1998/Accepted 10 June 1998

The Pseudomonas aeruginosa Mus clinical isolate produces OXA-18, a pI 5.5 class D extended-spectrum beta -lactamase totally inhibited by clavulanic acid (L. N. Philippon, T. Naas, A.-T. Bouthors, V. Barakett, and P. Nordmann, Antimicrob. Agents Chemother. 41:2188-2195, 1997). A second beta -lactamase was cloned, and the recombinant Escherichia coli clone pPL10 expressed a pI 7.4 beta -lactamase which conferred high levels of amoxicillin and ticarcillin resistance and which was partially inhibited by clavulanic acid. The 2.5-kb insert from pPL10 was sequenced, and a 266-amino-acid protein (OXA-20) was deduced; this protein has low amino acid identity with most of the class D beta -lactamases except OXA-2, OXA-15, and OXA-3 (75% amino acid identity with each). OXA-20 is a restricted-spectrum oxacillinase and is unusually inhibited by clavulanic acid. OXA-20 is a peculiar beta -lactamase because its translation initiates with a TTG (leucine) codon, which is rarely used as a translational origin in bacteria. Exploration of the genetic environment of oxa20 revealed the presence of the following integron features: (i) a second antibiotic resistance gene, aacA4; (ii) an intI1 gene; and (iii) two 59-base elements, each associated with either oxa20 or aacA4. This integron is peculiar because it lacks the 3' conserved region, and therefore is not a sul1-associated integron like most of them, and because its 3' end is located within tnpR, a gene involved in the transposition of Tn5393, a gram-negative transposon. P. aeruginosa Mus produces two novel and unrelated oxacillinases, OXA-18 and OXA-20, both of which are inhibited by clavulanic acid.

* Corresponding author. Mailing address: Service de Bactériologie-Virologie, Hôpital Antoine Béclère, 157 rue de-la-Porte de-Trivaux, 92141 Clamart Cedex, France. Phone: 33-1-45-37-42-98. Fax: 33-1-46-32-67-96. E-mail: Thierry.Naas{at}kb.u-psud.fr.

Antimicrobial Agents and Chemotherapy, August 1998, p. 2074-2083, Vol. 42, No. 8
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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