title: OXY-2-15, a novel variant showing increased ceftazidime hydrolytic activity.
abstract: OBJECTIVE
  Klebsiella oxytoca is a member of the family of Enterobacteriaceae and often contains the β-lactamase blaOXY gene. Although this β-lactamase does not naturally hydrolyse ceftazidime, this study describes possible in vivo selection of a clinical K. oxytoca isolate showing increased MICs of ceftazidime.
  
  
  METHODS
  To reveal the molecular mechanism underlying this unusual resistance phenotype, WGS, cloning, overexpression, MIC and steady-state kinetic studies were performed.
  
  
  RESULTS
  A patient was treated for a septic episode with ceftazidime (4 g/day). This therapy was based on earlier culture results in which, amongst others, a K. oxytoca (Velp-1) isolate was identified. After 11 days of treatment, K. oxytoca Velp-2 was isolated from a pus sample drained from the wound. The isolate showed increased resistance to ceftazidime (MIC ≥64 mg/L) compared with the original K. oxytoca isolate (Velp-1). WGS revealed the presence of a novel blaOXY-2 allele, designated blaOXY-2-15, with a two amino acid deletion at Ambler positions 168 and 169 compared with OXY-2-2. Cloning blaOXY-2-15 into Escherichia coli TOP10 resulted in increased MICs of ceftazidime, but reduced MICs of most other β-lactams compared with OXY-2-2. Steady-state kinetics confirmed the results of the MIC data, showing clearly significant ceftazidime hydrolysis.
  
  
  CONCLUSIONS
  This report shows the risk of in vivo selection of ceftazidime-resistant K. oxytoca isolates after prolonged ceftazidime treatment. Furthermore, it is the first known report of a K. oxytoca isolate conferring resistance to ceftazidime by a two amino acid deletion in the omega loop of OXY-2-2.
authors: Laboratory for Medical Microbiology and Immunology, Rijnstate, Velp, The Netherlands rht.nijhuis@outlook.com.
authors: R H T
authors: RH
authors: Nijhuis
authors: Bactériologie-Virologie, AP-HP, LabEx LERMIT, Univ. Paris-Sud, Paris, France.
authors: S
authors: S
authors: Oueslati
authors: Molecular Unit, Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors: K
authors: K
authors: Zhou
authors: Laboratory for Medical Microbiology and Immunology, Rijnstate, Velp, The Netherlands.
authors: R W
authors: RW
authors: Bosboom
authors: Molecular Unit, Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors: J W A
authors: JW
authors: Rossen
authors: Bactériologie-Virologie, AP-HP, LabEx LERMIT, Univ. Paris-Sud, Paris, France.
authors: T
authors: T
authors: Naas
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D002442:Ceftazidime / Q000378:metabolism* / Q000494:pharmacology; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D016680:Genome, Bacterial; D006801:Humans; D006868:Hydrolysis; D007710:Klebsiella Infections / Q000188:drug therapy / Q000382:microbiology; D041121:Klebsiella oxytoca / Q000187:drug effects* / Q000201:enzymology* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D012641:Selection, Genetic; D018805:Sepsis / Q000188:drug therapy / Q000382:microbiology; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D002442:Ceftazidime; D001618:beta-Lactamases
keywords: ESBLs; Enterobacteriaceae; Gram-negative; K1; KOXY; antimicrobial resistance mechanisms; bla genes