Lethality of Brucella microtiin a murine model of infection depends on the wbkEgene involved in O-polysaccharide synthesis

ABSTRACTBrucella microtiwas isolated a decade ago from wildlife and soil in Europe. Compared to the classical Brucellaspecies, it exhibits atypical virulence properties such as increased growth in human and murine macrophages and lethality in experimentally infected mice. A spontaneous rough (R) mutant strain, derived from the smooth reference strain CCM4915T, showed increased macrophage colonization and was non-lethal in murine infections. Whole-genome sequencing and construction of an isogenic mutant of B. microtiand Brucella suis1330 revealed that the R-phenotype was due to a deletion in a single gene, namely wbkE(BMI_I539), encoding a putative glycosyltransferase involved in lipopolysaccharide (LPS) O-polysaccharide biosynthesis. Complementation of the R-strains with the wbkEgene restored the smooth phenotype and the ability of B. microtito kill infected mice. LPS with an intact O-polysaccharide is therefore essential for lethal B. microtiinfections in the murine model, demonstrating its importance in pathogenesis.