Structure and genetics of the O ‐antigen of C ronobacter turicensis G 3882 from a new serotype, C . turicensis O 2, and identification of a serotype‐specific gene

Lipopolysaccharides on the cell surface of G ram‐negative bacteria are an important factor in pathogenicity, and the O ‐specific polysaccharide chain ( O ‐polysaccharide, O ‐antigen) defines the immunospecificity of different bacterial strains. C ronobacter turicensis is an emerging foodborne pathogen which causes severe invasive infections in neonates. In this study, a new O serotype, C . turicensis O 2, was established, the structure and genetics of the O ‐antigen were investigated, and a serotype‐specific gene was identified. Sugar and methylation analyses, and nuclear magnetic resonance spectroscopy indicated that the O ‐polysaccharide contains d ‐galactose ( d ‐ G al), N ‐acetyl‐ d ‐glucosamine ( d ‐ G lc NA c), l‐ rhamnose ( l ‐ R ha) and 5,7‐diacetamido‐3,5,7,9‐tetradeoxy‐ d ‐ glycero ‐ d ‐ galacto ‐non‐2‐ulosonic acid (di‐ N ‐acetyllegionaminic acid, L eg5 A c7 A c). The structure of the tetrasaccharide repeat of the O ‐polysaccharide was established as:. 5 mm→4 ) ‐ α ‐Leg p 5 Ac 7 Ac‐ ( 2→3 ) ‐ α ‐ d ‐Gal p ‐ ( 1→3 ) ‐ β ‐ l ‐Rha p ‐ ( 1→4 ) ‐ β ‐ d ‐Glc p NAc‐ ( 1→The O ‐antigen gene cluster of C . turicensis O 2 was sequenced and compared with related gene clusters from available databases. Putative genes for the synthesis of l ‐ R ha and L eg5 A c7 A c, and genes encoding sugar transferases and O ‐antigen processing genes ( wzx and wzy ) were found. The tentatively assigned functions of the O ‐antigen genes were in agreement with the structure of the O ‐polysaccharide. In addition, primers based on the wzy gene were shown to be specific for C . turicensis O 2 in a screen against 145 strains.