Detection of Burkholderia pseudomallei O-antigen serotypes in near-neighbor species.

BACKGROUND: Burkholderia pseudomallei is the etiological agent of melioidosis and a CDC category B select agent with no available effective vaccine. Previous immunizations in mice have utilized the lipopolysaccharide (LPS) as a potential vaccine target because it is known as one of the most important antigenic epitopes in B. pseudomallei. Complicating this strategy are the four different B. pseudomallei LPS O-antigen types: A, B, B2, and rough. Sero-crossreactivity is common among O-antigens of Burkholderia species. Here, we identified the presence of multiple B. pseudomallei O-antigen types and sero-crossreactivity in its near-neighbor species. RESULTS: PCR screening of O-antigen biosynthesis genes, phenotypic characterization using SDS-PAGE, and immunoblot analysis showed that majority of B. mallei and B. thailandensis strains contained the typical O-antigen type A. In contrast, most of B. ubonensis and B. thailandensis-like strains expressed the atypical O-antigen types B and B2, respectively. Most B. oklahomensis strains expressed a distinct and non-seroreactive O-antigen type, except strain E0147 which expressed O-antigen type A. O-antigen type B2 was also detected in B. thailandensis 82172, B. ubonensis MSMB108, and Burkholderia sp. MSMB175. Interestingly, B. thailandensis-like MSMB43 contained a novel serotype B positive O-antigen. CONCLUSIONS: This study expands the number of species which express B. pseudomallei O-antigen types. Further work is required to elucidate the full structures and how closely these are to the B. pseudomallei O-antigens, which will ultimately determine the efficacy of the near-neighbor B serotypes for vaccine development.

Structural characterization of polysaccharides expressed by Burkholderia oklahomensis E0147.

Burkholderia oklahomensis E0147 is a US isolated bacterium believed to express a similar O-antigen to type A structure of the highly pathogenic species, Burkholderia pseudomallei. Both species are genetically closely related. Lipopolysaccharide was collected from E0147 and structurally characterized to test this hypothesis. Glycosyl composition and linkage analyses in conjunction with 1D and 2D (1)H and (13)C NMR spectroscopy showed that the O-antigen was a repeating disaccharide with the following structure: [3)-ß-D-Glcp-(1→3)-2OAc-α-L-6dTalp-(1→]n NMR spectroscopy also revealed the presence of a co-extracted exopolysaccharide previously described in B. pseudomallei, with the structure: [3)-2OAc-ß-D-Galp-(1→4)-α-D-Galp-(1→3)-ß-D-Galp-(1→5)-ß-D-Kdop-(2→]n.