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Antimicrobial Agents and Chemotherapy, March 2000, p. 561-567, Vol. 44, No. 3
Department of Microbiology, Kitasato
University School of Medicine, 1-15-1 Kitasato, Sagamihara,
Kanagawa 228-8555, Japan
Received 26 August 1999/Returned for modification 12 November
1999/Accepted 8 December 1999
The ampC and ampR genes of
Enterobacter cloacae GN7471 were cloned into pMW218 to
yield pKU403. Four mutant plasmids derived from pKU403 (pKU404, pKU405,
pKU406, and pKU407) were isolated in an AmpD mutant of
Escherichia coli ML4953 by selection with ceftazidime or
aztreonam. The
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
ampR Gene Mutations That Greatly
Increase Class C
-Lactamase Activity in Enterobacter
cloacae
-lactamase activities expressed by pKU404, pKU405,
pKU406, and pKU407 were about 450, 75, 160, and 160 times higher,
respectively, than that expressed by the original plasmid, pKU403.
These mutant plasmids all carried point mutations in the
ampR gene. In pKU404 and pKU405, Asp-135 was changed to Asn
and Val, respectively. In both pKU406 and pKU407, Arg-86 was changed to
Cys. The ease of selection of AmpR mutations at a frequency of about
10
6 in this study strongly suggests that derepressed
strains, such as AmpD or AmpR mutants, could frequently emerge in the
clinical setting.
*
Corresponding author. Mailing address: Department of
Microbiology, Kitasato University School of Medicine, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan. Phone: 81-427-78-9355. Fax: 81-427-78-9350. E-mail: matsu{at}kitasato-u.ac.jp.
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