Structure of the O-polysaccharide from the lipopolysaccharide of Providencia alcalifaciens O48

► Providencia alcalifaciens is an opportunistic human pathogen. ► We isolated a lipopolysaccharide from a strain of P. alcalifaciens O48. ► An O-polysaccharide was released by mild acid delipidation of the lipopolysaccharide. ► It was studied by sugar and methylation analyses and 2D NMR spectroscopy. ► The structure of a tetrasaccharide repeat of the O-polysaccharide was established.