Klebsiella oxytoca complex: update on taxonomy, antimicrobial resistance, and virulence

Jing Yang, Haiyan Long, Ya Hu, Yu Feng, Alan McNally, Zhiyong Zong

Research output: Contribution to journalReview articlepeer-review


Klebsiella oxytoca is actually a complex of nine species-Klebsiella grimontii, Klebsiella huaxiensis, Klebsiella michiganensis, K. oxytoca, Klebsiella pasteurii, Klebsiella spallanzanii, and three unnamed novel species. Phenotypic tests can assign isolates to the complex, but precise species identification requires genome-based analysis. The K. oxytoca complex is a human commensal but also an opportunistic pathogen causing various infections, such as antibiotic-associated hemorrhagic colitis (AAHC), urinary tract infection, and bacteremia, and has caused outbreaks. Production of the cytotoxins tilivalline and tilimycin lead to AAHC, while many virulence factors seen in Klebsiella pneumoniae, such as capsular polysaccharides and fimbriae, have been found in the complex; however, their association with pathogenicity remains unclear. Among the 5,724 K. oxytoca clinical isolates in the SENTRY surveillance system, the rates of nonsusceptibility to carbapenems, ceftriaxone, ciprofloxacin, colistin, and tigecycline were 1.8%, 12.5%, 7.1%, 0.8%, and 0.1%, respectively. Resistance to carbapenems is increasing alarmingly. In addition to the intrinsic blaOXY, many genes encoding β-lactamases with varying spectra of hydrolysis, including extended-spectrum β-lactamases, such as a few CTX-M variants and several TEM and SHV variants, have been found. blaKPC-2 is the most common carbapenemase gene found in the complex and is mainly seen on IncN or IncF plasmids. Due to the ability to acquire antimicrobial resistance and the carriage of multiple virulence genes, the K. oxytoca complex has the potential to become a major threat to human health.

Original languageEnglish
Article numbere0000621
JournalClinical Microbiology Reviews
Issue number1
Early online date1 Dec 2021
Publication statusPublished - 19 Jan 2022

Bibliographical note

Funding Information:
Our relevant work was supported by the DETECTIVE project funded by the National Natural Science Foundation of China (81861138055) and the Medical Research Council (MR/S013660/1) and by a grant from the West China Hospital of Sichuan University (1.3.5 project for disciplines of excellence, grant ZYYC08006). We declare no conflict of interest.

Publisher Copyright:
Copyright © 2021 American Society for Microbiology. All Rights Reserved.


  • Infectious Diseases
  • Microbiology (medical)
  • Public Health, Environmental and Occupational Health
  • General Immunology and Microbiology
  • Epidemiology
  • Klebsiella
  • β-lactamases
  • taxonomy
  • carbapenemases
  • resistance
  • Klebsiella oxytoca
  • virulence
  • antimicrobial resistance

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health
  • Microbiology (medical)
  • Infectious Diseases
  • General Immunology and Microbiology
  • Epidemiology


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