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Antimicrobial Agents and Chemotherapy, 04 1997, 785-790, Vol 41, No. 4
F Danel, LM Hall, D Gur and DM Livermore
Pseudomonas aeruginosa AH, isolated in Ankara, Turkey, was highly resistant
to ceftazidime (MIC, 128 microg/ml) and produced a beta- lactamase that
gave a doublet of bands at pIs 8.7 and 8.9. beta- Lactamase production was
transferable to P. aeruginosa PU21 by conjugation and was determined by a
ca. 450-kb plasmid, pMLH54. The transconjugant and Escherichia coli
transformed with the cloned gene showed increased resistance to ceftazidime
(especially) and to cefpirome, ceftazidime, ceftriaxone, moxalactam, and
aztreonam, but not to carbapenems. Resistance was not reversed by
clavulanic acid or tazobactam. Sequencing revealed that the beta-lactamase
responsible for this resistance was identical to OXA-2 except that glycine
replaced aspartate at position 150. Compared to OXA-2, the new enzyme,
named OXA- 15, had greater cephalosporinase activity, with increased
relative hydrolysis rates for cephaloridine and cephalothin and, most
dramatically, for ceftazidime. Cefotaxime and carbapenems remained stable
to hydrolysis. Thus, as in the TEM, SHV, and OXA-10 (PSE-2) beta- lactamase
families, a minor sequence change in OXA-2 gave a major extension of
cephalosporinase activity and contingent resistance. The gene encoding the
new beta-lactamase, bla(OXA-15), lay close to the highly conserved 3' end
of an integron and had flanking sequences typical of an integron-associated
gene cassette. Restriction mapping and partial sequence data indicated that
pMLH54 carries an integron with three putative gene cassettes: bla(OXA-15)
itself, aadB [coding aminoglycoside nucleotidyltransferase (2")-1a], and an
uncharacterized cassette.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
OXA-15, an extended-spectrum variant of OXA-2 beta-lactamase, isolated from a Pseudomonas aeruginosa strain
Department of Medical Microbiology, St. Bartholomew's and the Royal London School of Medicine and Dentistry, London, United Kingdom. F.H.Danel@mds.qmw.ac.uk
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