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Antimicrobial Agents and Chemotherapy, December 1998, p. 3117-3122, Vol. 42, No. 12
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

OXA-16, a Further Extended-Spectrum Variant of OXA-10 beta -Lactamase, from Two Pseudomonas aeruginosa Isolates

Franck Danel,1,* Lucinda M. C. Hall,1 Deniz Gur,2 and David M. Livermore1,dagger

Antibiotic Group, Department of Medical Microbiology, St. Bartholomew's and the Royal London School of Medicine and Dentistry, London, E1 2AD, United Kingdom,1 and Section of Infectious Diseases, Department of Internal Medicine, Hacettepe University School of Medicine, 06100 Ankara, Turkey2

Received 13 March 1998/Returned for modification 14 July 1998/Accepted 21 September 1998

Two extended-spectrum mutants of the class D beta -lactamase OXA-10 (PSE-2) from Pseudomonas aeruginosa isolates obtained in Ankara, Turkey, were described previously and were designated OXA-11 and -14. P. aeruginosa 906 and 961, isolated at the same hospital, were highly resistant to ceftazidime (MIC >=  128 µg/ml) and produced a beta -lactamase with a pI of 6.2. The MICs of ceftriaxone, cefoperazone, cefsulodin, and cefepime were 4- to 16-fold above the typical values for P. aeruginosa, whereas the MICs of penicillins and cefotaxime were raised only marginally. Ceftazidime MICs were not significantly reduced by clavulanate or tazobactam at 4 µg/ml. Ceftazidime resistance did not transfer conjugatively but was mobilized to P. aeruginosa PU21 by plasmid pUZ8. Both isolates gave similar DNA restriction patterns, suggesting that they were replicates; moreover, they yielded identically sized BamHI fragments that hybridized with a blaOXA-10 probe. DNA sequencing revealed that both isolates had the same new beta -lactamase, designated OXA-16, which differed from OXA-10 in having threonine instead of alanine at position 124 and aspartate instead of glycine at position 157. The latter change is also present in OXA-11 and -14 and seems critical to ceftazidime resistance. Kinetic parameters showed that OXA-16 enzyme was very active against penicillins, cephaloridine, cefotaxime, and ceftriaxone, but hydrolysis of ceftazidime was not detected despite the ability of the enzyme to confer resistance.

* Corresponding author. Present address: F. Hoffmann-La Roche Ltd., Pharmaceuticals Division, Pharma Research Preclinical Infectious Disease, CH-4070 Basel, Switzerland. Phone: 41-61-6880537. Fax: 41-61-6882729. E-mail franck.danel{at}roche.com.

dagger Present address: Antibiotic Reference Unit, Laboratory of Hospital Infection, Central Public Health Laboratory, London NW9 5HT, United Kingdom.

Antimicrobial Agents and Chemotherapy, December 1998, p. 3117-3122, Vol. 42, No. 12
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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