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

<i>Klebsiella oxytoca</i> 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 <i>K</i>. <i>oxytoca</i> infections make these bacteria an emerging pathogen, which is still masked by the predominant <i>K</i>. <i>pneumoniae</i> isolates. Thus, it is very important to advance knowledge on <i>K</i>. <i>oxytoca</i> pathogenicity. This work aims to characterize a urine isolate, <i>K</i>. <i>oxytoca</i> 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 <i>K</i>. <i>oxytoca</i> 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-Man<i>p</i>) residues, one galactopyranose (β-Gal<i>p</i>) residue, and one galacturonic acid (α-Gal<i>p</i>A) residue. The Gal<i>p</i>A residue seems to be a potential minor epitope, recognized by the selected <i>Proteus</i> antisera in the serological studies.