Open AccessPrediction of the Evolution of Ceftazidime Resistance in Extended-Spectrum β-Lactamase CTX-M-9
Author(s) -
Julien Delmas,
Frédéric Robin,
Fernando Aécio de Amorim Carvalho,
Céline Mongaret,
Richard Bonnet
Publication year - 2006
Publication title -
antimicrobial agents and chemotherapy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.07
H-Index - 259
eISSN - 1070-6283
pISSN - 0066-4804
DOI - 10.1128/aac.50.2.731-738.2006
Subject(s) - ceftazidime , spectrum (functional analysis) , microbiology and biotechnology , biology , computational biology , genetics , physics , bacteria , pseudomonas aeruginosa , quantum mechanics
A random mutagenesis technique was used to predict the evolutionary potential of β-lactamase CTX-M-9 toward the acquisition of improved catalytic activity against ceftazidime. Thirty CTX-M mutants were obtained during three rounds of mutagenesis. These mutants conferred 1- to 128-fold-higher MICs of ceftazidime than the parental enzyme CTX-M-9. The CTX-M mutants contained one to six amino acid substitutions. Mutants harbored the substitutions Asp240Gly and Pro167Ser, which were previously observed in clinical CTX-M enzymes. Additional substitutions, notably Arg164His, Asp179Gly, and Arg276Ser, were observed near the active site. The kinetic constants of the three most active mutants revealed two distinct ways of improving catalytic efficiency against ceftazidime. One enzyme had a 17-fold-higherk cat value than CTX-M-9 against ceftazidime. The other two had 75- to 300-fold-lowerKm values than CTX-M-9 against ceftazidime. The current emergence of CTX-M β-lactamases with improved activity against ceftazidime may therefore be the beginning of an evolutionary process which might subsequently generate a great diversity of CTX-M-type ceftazidimases.