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Antimicrobial Agents and Chemotherapy, December 1998, p. 3117-3122, Vol. 42, No. 12
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
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
-Lactamase, from Two Pseudomonas
aeruginosa Isolates
-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
-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
-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.
Present address: Antibiotic Reference Unit, Laboratory of Hospital
Infection, Central Public Health Laboratory, London NW9 5HT, United Kingdom.
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