Lipopolysaccharides on the cell surface of Gram-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. Cronobacter turicensis is an emerging foodborne pathogen which causes severe invasive infections in neonates. In this study, a new O serotype, C. turicensis O2, 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-Gal), N-acetyl-d-glucosamine (d-GlcNAc), l-rhamnose (l-Rha) and 5,7-diacetamido-3,5,7,9-tetradeoxy-d-glycero-d-galacto-non-2-ulosonic acid (di-N-acetyllegionaminic acid, Leg5Ac7Ac). The structure of the tetrasaccharide repeat of the O-polysaccharide was established as:
The O-antigen gene cluster of C. turicensis O2 was sequenced and compared with related gene clusters from available databases. Putative genes for the synthesis of l-Rha and Leg5Ac7Ac, 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 O2 in a screen against 145 strains.