AUTHOR=Stojkovic Katarina , Szijártó Valéria , Kaszowska Marta , Niedziela Tomasz , Hartl Katharina , Nagy Gábor , Lukasiewicz Jolanta 

TITLE=Identification of d-Galactan-III As Part of the Lipopolysaccharide of Klebsiella pneumoniae Serotype O1

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.00684

DOI=10.3389/fmicb.2017.00684

ISSN=1664-302X

ABSTRACT=<p><italic>Klebsiella pneumoniae</italic> is a Gram-negative, ubiquitous bacterium capable of causing severe nosocomial infections in individuals with impaired immune system. Emerging multi-drug resistant strains of this species and particularly carbapenem-resistant strains pose an urgent threat to public health. The lipopolysaccharide (LPS) O-antigen is the main surface antigen. It contributes to the virulence of this species and determines the O-serotype of <italic>K. pneumoniae</italic> isolates. Among the nine main O-serotypes of <italic>K. pneumoniae</italic>, O1-and O2-type pathogens are causative agents of over 50% of all infections. Serotype O1, the most common O-serotype, expresses complex LPS consisting of <sc>d</sc>-galactan-I (a polymer built of → 3)-β-<sc>d</sc>-Gal<italic>f</italic>-(1 → 3)-α-<sc>d</sc>-Gal<italic>p</italic>-(1 → repeating units) capped by <sc>d</sc>-galactan-II (built of [ → 3)-α-<sc>d</sc>-Gal<italic>p</italic>-(1 → 3)-β-<sc>d</sc>-Gal<italic>p</italic>-(1 →] repeating units). Galactan-I is present as the sole polymer in O2 serotype. Recently, in case of serotype O2, conversion of galactan-I to galactan-III (→ 3)-β-<sc>d</sc>-Gal<italic>f</italic>-(1 → 3)-[α-<sc>d</sc>-Gal<italic>p</italic>-(1 → 4)]-α-<sc>d</sc>-Gal<italic>p</italic>-(1 →) was reported. Substitution of → 3)-α-<sc>d</sc>-Gal<italic>p</italic> by a branching terminal α-<sc>d</sc>-Gal<italic>p</italic> was dependent on the presence of the <italic>gmlABC</italic> operon and had a major impact on the antigenicity of the galactan polymer. Genetic analysis indicated that 40% of the O1 clinical isolates also carry the <italic>gmlABC</italic> locus; therefore we aimed to characterize the corresponding phenotype of LPS O-antigens. The presence of galactan-III among O1 strains was proven using galactan-III-specific monoclonal antibodies and confirmed by structural analyses performed using sugar and methylation analysis as well as classical and high-resolution magic angle spinning NMR spectroscopy. By using an isogenic mutant pair, we demonstrated that galactan-III expression was dependent on the presence of glycosyltransferases encoded by <italic>gmlABC</italic>, as was shown previously for the O2 serotype. Furthermore, the galactan-II structures in O1<italic>gml</italic>+ strains remained unaffected corroborating no functional interactions between the biosynthesis of galactan-III and galactan-II polymers.</p>