OXA-17, a further extended-spectrum variant of OXA-10 beta-lactamase, isolated from Pseudomonas aeruginosa.
Pseudomonas aeruginosa isolates 871 and 873 were isolated at Hacettepe University Hospital in Ankara and were highly resistant to ceftazidime (MIC, 128 microg/ml). Each produced three beta-lactamases, with pIs of 5.3, 6.1, and 7.9. The beta-lactamase with a pI of 5.3 was previously shown to be PER-1 enzyme. The antibiograms of the isolates were not entirely explained by production of PER-1 enzyme, insofar as ceftazidime resistance was incompletely reversed by clavulanate. The enzymes with pIs of 6.1 and 7.9 were therefore investigated. The enzyme with a pI of 6.1 proved to be a novel mutant of OXA-10, which we designated OXA-17, and had asparagine changed to serine at position 73 of the protein. When cloned into Escherichia coli XL1-blue, OXA-17 enzyme conferred greater resistance to cefotaxime, latamoxef, and cefepime than did OXA-10, but it had only a marginal (two- to fourfold) effect on the MIC of ceftazidime. This behavior contrasted with that of previous OXA-10 mutants, specifically OXA-11, -14, and -16, which predominately compromise ceftazidime. Extracted OXA-17 enzyme had relatively greater activity than OXA-10 against oxacillin, cloxacillin, and cefotaxime but, in terms of kcat/Km, it had lower catalytic efficiency against most beta-lactams. The enzyme with a pI of 7.9 was shown by gene sequencing to be OXA-2.
Danel
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Antibiotic Group, Department of Medical Microbiology, St. Bartholomew's and the Royal London School of Medicine and Dentistry, London, E1 2AD, United Kingdom. franck.danel@roche.com
Hall
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Duke
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Gur
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Livermore
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D000900:Anti-Bacterial Agents / Q000494:pharmacology; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000187:drug effects; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000201:enzymology*; D001618:beta-Lactamases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D047090:beta-Lactams
D000900:Anti-Bacterial Agents; D047090:beta-Lactams; C039404:beta-lactamase OXA-2; D001618:beta-Lactamases