Characterization of CTX-M-140, a Variant of CTX-M-14 Extended-Spectrum β-Lactamase with Decreased Cephalosporin Hydrolytic Activity, from Cephalosporin-Resistant Proteus mirabilis
Threonine
0301 basic medicine
Base Composition
Alanine
Hydrolysis
Gene Expression
Microbial Sensitivity Tests
Recombinant Proteins
beta-Lactamases
Anti-Bacterial Agents
Cephalosporins
3. Good health
Isoenzymes
03 medical and health sciences
Amino Acid Substitution
Genome Size
Drug Resistance, Bacterial
Mutation
Escherichia coli
Cloning, Molecular
Proteus mirabilis
Genome, Bacterial
DOI:
10.1128/aac.00822-16
Publication Date:
2016-08-02T03:04:34Z
AUTHORS (12)
ABSTRACT
ABSTRACT
CTX-M-140, a novel CTX-M-type extended-spectrum β-lactamase (ESBL), was identified in cephalosporin-resistant clinical isolates of
Proteus mirabilis
. CTX-M-140 contained an alanine-to-threonine substitution at position 109 compared to its putative progenitor, CTX-M-14. When it was expressed in an
Escherichia coli
isogenic background, CTX-M-140 conferred 4- to 32-fold lower MICs of cephalosporins than those with CTX-M-14, indicating that the phenotype was attributable to this single substitution. For four mutants of CTX-M-14 that were constructed by site-directed mutagenesis (A109E, A109D, A109K, and A109R mutants), MICs of cephalosporins were similar to those for the
E. coli
host strain, which suggested that the alanine at position 109 was essential for cephalosporin hydrolysis. The kinetic properties of native CTX-M-14 and CTX-M-140 were consistent with the MICs for the
E. coli
clones. Compared with that of CTX-M-14, a lower hydrolytic activity against cephalosporins was observed for CTX-M-140.
bla
CTX-M-140
is located on the chromosome as determined by I-CeuI pulsed-field gel electrophoresis (I-CeuI-PFGE) and Southern hybridization. The genetic environment surrounding
bla
CTX-M-140
is identical to the sequence found in different plasmids with
bla
CTX-M-9-group
genes among the
Enterobacteriaceae
. Genome sequencing and analysis showed that
P. mirabilis
strains with
bla
CTX-M-140
have a genome size of ∼4 Mbp, with a GC content of 38.7% and 23 putative antibiotic resistance genes. Our results indicate that alanine at position 109 is critical for the hydrolytic activity of CTX-M-14 against oxyimino-cephalosporins.
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