Genotypic and phenotypic characterisation of the Klebsiella oxytoca complex

Klebsiella spp. are associated with 3 to 7% of nosocomial infections and can be responsible for a range of conditions including pneumonia, bloodstream infections, meningitis, and necrotizing enterocolitis in infants. The role of Klebsiella pneumoniae in causing disease is well-characterised but, to date, the closely related species Klebsiella oxytoca has not received the same attention, despite often encoding extended-spectrum beta-lactamases and carbapenemases in clinical settings. K. oxytoca is the causative agent of Clostridiodes difficile-negative antibiotic-associated haemorrhagic colitis, a rare condition seen in some individuals receiving antibiotics. Whole-genome sequence analyses have shown K. oxytoca to be a complex comprising at least six species (K. oxytoca, K. michiganensis, K. grimontii, K. huaxiensis, ‘K. pasteurii’, ‘K. spallanzanii’). Our study aims to better characterise the K. oxytoca complex using a polyphasic approach. Preliminary investigations into the genomes of three K. michiganensis clinical isolates revealed the presence of a plasmid-borne ccdABlocus. ccdAB is a toxin-antitoxin (TA) system known to maintain plasmids in other pathogenic enterobacteria. We aim to functionally validate this TA system by cloning and conducting toxicity assays on the CcdB toxin, and cloning and assessing the ability of CcdA to function as an antidote. We also aim to sequence and generate Illumina/Oxford Nanopore hybrid genome assemblies of a larger collection of K. oxytoca complex clinical isolates and investigate their plasmids and TA systems in the same manner.