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Antimicrobial Agents and Chemotherapy, Feb 1997, 374-378, Vol 41, No. 2
MM Canica, M Barthelemy, L Gilly, R Labia, R Krishnamoorthy and G Paul
IRT-14 (TEM-45) is a new mutant TEM-type beta-lactamase that was isolated
from clinical Escherichia coli P37 and that confers resistance to
broad-spectrum penicillins with reduced sensitivity to beta- lactamase
inhibitors. The MICs of amoxicillin alone and of amoxicillin combined with
2 micrograms of clavulanic acid or 2 micrograms of tazobactam per ml were
4,096, 2,048, and 1,024 micrograms/ml, respectively. The strain was
susceptible to cephalosporins, aztreonam, moxalactam, and imipenem. The
enzyme was purified to homogeneity, and values of the kinetic parameters
Kcat, Km, and Kcat/Km were determined for different substrates. This
enzyme, with a pI of 5.2, was found to have reduced affinity for
broad-spectrum penicillins and cephalosporins. The values of 50% inhibitory
concentrations of clavulanic acid, sulbactam, tazobactam, and brobactam are
correlated with the higher KmS for substrates. The resistance of E. coli
P37 to mechanism-based inactivators results from a higher level of
production of the TEM-derived enzyme due to the G-to-T substitution at
position 162 (G-162-->T) in the promoter region of blaTEM and from the
structural modifications resulting from the Met-69-->Leu and Arg-275--
>Gln substitutions that characterize IRT-14 beta-lactamase.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Properties of IRT-14 (TEM-45), a newly characterized mutant of TEM-type beta-lactamases
INSERM U 120, Hopital Robert Debre, Paris, France.
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