biostudies-literatureYang JUKRI | Medical Research Council (MRC)National Natural Science Foundation of China (NSF)Medical Research CouncilNational Natural Science Foundation of ChinaUKRI | Medical Research Councile0000621https://www.ebi.ac.uk/biostudies/studies/S-EPMC8635272biostudies-literatureUnknown35(1)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 assocClinical microbiology reviewsKlebsiella oxytoca Complex: Update on Taxonomy, Antimicrobial Resistance, and Virulence.PMC863527281861138055MR/S013660/1Yang JLong HHu YFeng YMcNally AZong ZfalseKlebsiella oxytoca Complex: Update on Taxonomy, Antimicrobial Resistance, and Virulence.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 assoc2022-01-01T00:00:00Z2022 Jan2025-04-19T15:40:27.464Z2025-04-19T15:40:27.464ZS-EPMC86352723485113410.1128/CMR.00006-2110.1128/cmr.00006-21