Deletion of glycosyltransferase galE impairs the InlB anchoring and pathogenicity of Listeria monocytogenes.

Listeria monocytogenes (L. monocytogenes) is a foodborne intracellular pathogen that causes serious disease in both humans and animals. InlB is the major internalin protein of L. monocytogenes, which anchors to the bacterial surface and mediates its invasion into various host cells. Recent studies have shown that galactosylation of the cell wall polymer wall teichoic acid (WTA) is essential for InlB anchoring on the cell surface of L. monocytogenes serotype 4b strains. Galactosylation of WTA is exerted by the coordinated action of several glycosyltransferases, including GalU, GalE, GtcA, GttA, and GttB. Among these glycosyltransferases, GttA and GttB are specific to serotype 4b strains, whereas GalE, GalU, and GtcA are conserved across all serotypes. The role of GalE in InlB anchoring and L. monocytogenes pathogenicity remains unclear. In this study, we deleted the galE gene, which is involved in galactosylation, from L. monocytogenes strain ScottA. We found that galE deletion reduced InlB anchoring, weakened bacterial adhesion and invasion of Caco-2 cells (human colorectal adenocarcinoma cells) and MGC803 cells (human gastric carcinoma cells), increased phagocytosis but decreased proliferation in RAW264.7 cells (mouse mononuclear macrophage leukaemia cells), and decreased bacteria load, mortality, and tissue damage in infected mice. Taken together, galE deletion significantly reduced the anchoring of InlB and weakened the pathogenicity of L. monocytogenes. This finding provides new insights into the correlation between cell wall modification and pathogenicity of L. monocytogenes.