Genetic and biochemical characterisation of CTX-M-37 extended-spectrum β-lactamase from an Enterobacter cloacae clinical isolate from Mongolia

Kyungwon Lee, Dongeun Yong, Seok Hoon Jeong, Khosbayar Tulgaa, Jean Denis Docquier, Gian Maria Rossolini, Yunsop Chong

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Objectives The aims of this study were to determine the resistance level of a bla CTX-M-37 -carrying Enterobacter cloacae isolate from Mongolia, to analyse kinetic parameters of the purified enzyme and to compare the genetic environment of the gene. Methods Minimum inhibitory concentrations (MICs) were determined using the Clinical and Laboratory Standards Institute (CLSI) agar dilution method. Purified CTX-M-37 enzyme was used to determined kinetic parameters. The genetic environment of the blaCTX-M-37 gene in E. cloacae was compared with a Kluyvera cryocrescens isolate. Results The E. cloacae isolate showed relatively low-level resistance to cefotaxime (MIC = 16 mg/L) compared with a CTX-M-3-producing strain (MIC = 256 mg/L), and CTX-M-37 had a lower k cat /K m value for cefotaxime (2.0 μM −1  s −1 ) compared with CTX-M-3 (3.5 μM −1  s −1 ), possibly due to Asn114Asp substitution. The bla CTX-M-37 gene in the E. cloacae isolate was carried on a conjugative plasmid and was associated with an ISEcp1 element containing the −35 and −10 putative promoter sequences TTGAAA and TACAAT, respectively, unlike in the K. cryocrescens isolate. Conclusions The CTX-M-37-producing E. cloacae isolate showed relatively low-level resistance to cefotaxime and the purified enzyme had lower kinetic parameters as the result of Asn114Asp substitution. Presence of an ISEcp1 element and putative promoters upstream of the bla CTX-M-37 gene in E. cloacae, but not in the K. cryocrescens isolate, indicated their roles in mobilisation and expression of the gene.

Original languageEnglish
Pages (from-to)3-7
Number of pages5
JournalJournal of Global Antimicrobial Resistance
Publication statusPublished - 2017 Sep


All Science Journal Classification (ASJC) codes

  • Microbiology
  • Immunology and Allergy
  • Immunology
  • Microbiology (medical)

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