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The dlt operon of Gram‐positive bacteria comprises four genes (dltA, dltB, dltC and dltD) that catalyse the incorporation of D‐alanine residues into the cell wall‐associated lipoteichoic acids (LTAs). In this work, we characterized the dlt operon of Listeria monocytogenes and constructed a D‐Ala‐deficient LTA mutant by inactivating the first gene (dltA) of this operon. The DltA⁻ mutant did not show any morphological alterations and its growth rate was similar to that of the wild‐type strain. However, it exhibited an increased susceptibility to the cationic peptides colistin, nisin and polymyxin B. The virulence of the DltA⁻ mutant was severely impaired in a mouse infection model (4 log increase in the LD₅₀) and, in vitro, the adherence of the mutant to various cell lines (murine bone marrow‐derived macrophages and hepatocytes and a human epithelial cell line) was strongly restricted, although the amounts of surface …