The lipopolysaccharide outer core of Yersinia enterocolitica serotype O : 3 is required for virulence and plays a role in outer membrane integrity

Lipopolysaccharide (LPS) of Yersinia enterocolitica O:3 has an inner core l inked to both the O-antigen and to an outer core hexasaccharide that forms a branch. The biological role of the outer core was studied using polar and non-polar mutants of the outer core biosynthetic operon, Analysis of O-ant igen- and outer core-deficient strains suggested a critical role for the ou ter core in outer membrane properties relevant in resistance to antimicrobi al peptides and permeability to hydrophobic agents, and indirectly relevant in resistance to killing by normal serum, Wild-type bacteria but not outer core mutants killed intragastrically infected mice, and the intravenous le thal dose was approximate to 10(4)-fold higher for outer core mutants, Afte r intragastric infection, outer core mutants colonized Peyer's patches and invaded mesenteric lymph nodes, spleen and liver, and induced protective im munity against wild-type bacteria. In mice co-infected intragastrically wit h an outer core mutant-wild type mixture, both strains colonized Peyer's pa tches similarly during the first 2 days, but the mutant was much less effic ient in colonizing deeper organs and was cleared faster from Peyer's patche s. The results demonstrate that outer core is required for Y. enterocolitic a O:3 full virulence, and strongly suggest that it provides resistance agai nst defence mechanisms (most probably those involving bactericidal peptides ).