# The First Report on the Structure of Polysaccharide Surface Antigens of the Clinical Klebsiella oxytoca 0.062 Strain and the Contribution in the Serological Cross-Reactions

## TL;DR

This paper reports the structure of polysaccharide antigens in a clinical Klebsiella oxytoca strain and their role in serological cross-reactions.

## Contribution

The study provides the first structural characterization of surface antigens in K. oxytoca and identifies a potential epitope for serological cross-reactions.

## Key findings

- Two polysaccharide antigens were identified in K. oxytoca 0.062: a neutral mannan and an acidic branched tetrasaccharide.
- The acidic antigen contains galacturonic acid, which may act as a minor epitope in cross-reactions with Proteus antisera.

## Abstract

Klebsiella oxytoca bacilli co-form the human intestinal microbiota, but in favorable conditions, they may also affect immunocompromised individuals, causing urinary tract infections, bacteremia, or antibiotic-associated hemorrhagic colitis. The growing numbers of clinical outbreaks of K. oxytoca infections make these bacteria an emerging pathogen, which is still masked by the predominant K. pneumoniae isolates. Thus, it is very important to advance knowledge on K. oxytoca pathogenicity. This work aims to characterize a urine isolate, K. oxytoca 0.062, from central Poland, which appears to present a multidrug-resistant and extended-spectrum β-lactamases-positive phenotype. The structural experiments include sugar and methylation analyses, mass spectrometry, and 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy. Additionally, 1H,1H ROESY, and 1H,13C HMBC experiments were carried out on the high-molecular-weight O polysaccharide fraction of K. oxytoca lipopolysaccharides (LPSs). These analyses led to the detection of two polysaccharide antigens: one neutral, containing a linear trisaccharide unit called mannan, and one acidic, which is built up of a branched tetrasaccharide unit containing two mannopyranose (α-Manp) residues, one galactopyranose (β-Galp) residue, and one galacturonic acid (α-GalpA) residue. The GalpA residue seems to be a potential minor epitope, recognized by the selected Proteus antisera in the serological studies.