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Antimicrobial Agents and Chemotherapy, July 1998, p. 1581-1586, Vol. 42, No. 7
Bayer AG, Institut für Antiinfektiva
Forschung, D-42096 Wuppertal, Germany
Received 14 January 1998/Returned for modification 5 March
1998/Accepted 3 May 1998
BAY 10-8888, a cyclic
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Decreased Accumulation or Increased Isoleucyl-tRNA Synthetase
Activity Confers Resistance to the Cyclic
-Amino Acid BAY
10-8888 in Candida albicans and Candida
tropicalis
-amino acid, exerts its antifungal
activity by inhibition of isoleucyl-tRNA synthetase activity after accumulation to a millimolar concentration inside the cell. We have
selected and characterized BAY 10-8888-resistant Candida albicans mutants. Reduced BAY 10-8888 accumulation as well as increased isoleucyl-tRNA synthetase activity was observed in these mutants. Some of the mutants were cross-resistant to cispentacin, a
structurally related
-amino acid, while sensitivities to
5-fluorocytosine and fluconazole remained unchanged in all mutants. All
except two in vitro-resistant mutants were pathogenic in a murine
candidiasis model, and BAY 10-8888 failed to cure the infection.
Furthermore, we have characterized BAY 10-8888 transport and
isoleucyl-tRNA synthetase activity in several Candida
tropicalis strains which showed MICs higher than those of other
Candida strains. An analysis of the C. tropicalis strains
revealed that intracellular concentrations of BAY 10-8888 were in the
millimolar range, comparable to those for C. albicans.
However, these isolates expressed isoleucyl-tRNA synthetase activities
about fourfold higher than those for C. albicans. To test
the possibility of resistance modeling, we determined the correlations
between the intracellular concentration of BAY 10-8888, the specific
activity of isoleucyl-tRNA synthetase, the number of free, i.e.,
noninhibited, isoleucyl-tRNA synthetase molecules/cell, and growth,
assuming a linear relation. We found significant correlations between
growth and the intracellular concentration of BAY 10-8888 and between
growth and the number of free isoleucyl-tRNA synthetase molecules/cell,
but not between growth and the specific activity of isoleucyl-tRNA
synthetase.
*
Corresponding author. Mailing address: Bayer Yakuhin
Ltd., Research Center Kyoto, 6-5-1-3 Kunimidai, Kizu-cho, Soraku-gun, Kyoto 619-02, Japan. Phone: (81)774 75-2462. Fax: (81)774 75-2507. E-mail: karl.ziegelbauer.kz{at}bayer-ag.de.
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