The Contribution of Polysaccharide Antigens From Clinical Proteus spp. and Klebsiella spp. Isolates to the Serological Cross-Reactions

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

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.

Structural and Serological Characterization of Yet Another New O Antigen, O86, in Proteus mirabilis Clinical Strains

Bacteria from the genus Proteus are facultative human pathogens, primarily attacking the urinary tract and wounds. A total of 85 O serogroups have been identified so far among these bacilli. P. mirabilis Bprz 86 was isolated from the fistula of a patient in Łódź, Poland. Enzyme-Linked Immunosorbent Assay (ELISA) and Western blotting studies involving the P. mirabilis Bprz 86 lipopolysaccharide (LPS) and the strain-specific rabbit antiserum indicated that the strain, which does not belong to any of the O1-O85 serogroups, shares a common epitope with Proteus O17 antigens and is identical to another clinical P. mirabilis strain, Sm 120, isolated from the urine of a patient in the area. The O-specific polysaccharide (O antigen) was obtained from P. mirabilis Bprz 86 LPS through mild acid degradation, and the six-constituent structure of its repeating unit was determined using chemical analyses and 1D and 2D 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy. It includes (R)-3-hydroxybutanoyl, which, along with fucosamine and glucose residues, forms a fragment also present in the O17 antigens. Based on the obtained serological and chemical data, the two studied P. mirabilis isolates were proposed as candidates for a new successive O serogroup in the genus Proteus, O86.

Proteus mirabilis and Klebsiella pneumoniae as pathogens capable of causing co-infections and exhibiting similarities in their virulence factors

The genera Klebsiella and Proteus were independently described in 1885. These Gram-negative rods colonize the human intestinal tract regarded as the main reservoir of these opportunistic pathogens. In favorable conditions they cause infections, often hospital-acquired ones. The activity of K. pneumoniae and P. mirabilis, the leading pathogens within each genus, results in infections of the urinary (UTIs) and respiratory tracts, wounds, bacteremia, affecting mainly immunocompromised patients. P. mirabilis and K. pneumoniae cause polymicrobial UTIs, which are often persistent due to the catheter biofilm formation or increasing resistance of the bacteria to antibiotics. In this situation a need arises to find the antigens with features common to both species. Among many virulence factors produced by both pathogens urease shows some structural similarities but the biggest similarities have been observed in lipids A and the core regions of lipopolysaccharides (LPSs). Both species produce capsular polysaccharides (CPSs) but only in K. pneumoniae these antigens play a crucial role in the serological classification scheme, which in Proteus spp. is based on the structural and serological diversity of LPS O-polysaccharides (OPSs). Structural and serological similarities observed for Klebsiella spp. and Proteus spp. polysaccharides are important in the search for the cross-reacting vaccine antigens.