Molecular characterization of OXA-20, a novel class D beta-lactamase, and its integron from Pseudomonas aeruginosa.
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.
Service de Bactériologie-Virologie, Hôpital Antoine Béclère, Faculté de Médecine Paris-Sud, 92141 Clamart Cedex, France. Thierry.Naas@kb.u-psud.fr
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D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004251:DNA Transposable Elements; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D001618:beta-Lactamases / Q000235:genetics*
D004251:DNA Transposable Elements; D001618:beta-Lactamases