Molecular characterization of a cephamycin-hydrolyzing and inhibitor-resistant class A β-lactamase, GES-4, possessing a single G170S substitution in the ω-loop

Jun Ichi Wachino, Yohei Doi, Kunikazu Yamane, Naohiro Shibata, Tetsuya Yagi, Takako Kubota, Yoshichika Arakawa

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The nosocomial spread of six genetically related Klebsiella pneumoniae strains producing GES-type β-lactamases was found in a neonatal intensive care unit, and we previously reported that one of the six strains, strain KG525, produced a new β-lactamase, GES-3. In the present study, the molecular mechanism of cephamycin resistance observed in strain KG502, one of the six strains described above, was investigated. This strain was found to produce a variant of GES-3, namely, GES-4, which was responsible for resistance to both cephamycins (cefoxitin MIC, >128 μg/ml) and β-lactamase inhibitors (50% inhibitory concentration of clavulanic acid, 15.2 ± 1.7 μM). The GES-4 enzyme had a single G170S substitution in the Ω-loop region compared with the GES-3 sequence. This single amino acid substitution was closely involved with the augmented hydrolysis of cephamycins and carbapenems and the decreased affinities of β-lactamase inhibitors to GES-4. A cloning experiment and sequencing analysis revealed that strain KG502 possesses duplicate blaGES-4 genes mediated by two distinct class 1 integrons with similar gene cassette configurations. Moreover, the genetic environments of the blaGES-4 genes found in strain KG502 were almost identical to that of blaGES-3 in strain KG525. From these findings, these two phenotypically different strains were suggested to belong to a clonal lineage. The blaGES-4 gene found in strain KG502 might well emerge from a point mutation in the blaGES-3 gene harbored by its ancestor strains, such as strain KG525, under heavy antibiotic stress in order to acquire extended properties of resistance to cephamycins and carbapenems.

Original languageEnglish
Pages (from-to)2905-2910
Number of pages6
JournalAntimicrobial Agents and Chemotherapy
Issue number8
Publication statusPublished - 01-08-2004
Externally publishedYes


All Science Journal Classification (ASJC) codes

  • Pharmacology
  • Pharmacology (medical)
  • Infectious Diseases

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