Attenuated virulence of Streptococcus agalactiae deficient in D‐alanyl‐lipoteichoic acid is due to an increased susceptibility to defensins and phagocytic cells

D‐alanylation of lipoteichoic acid (LTA), allows Gram‐positive bacteria to modulate their surface charge, regulate ligand binding and control the electromechanical properties of the cell wall. In this study, the role of D‐alanyl LTA in the virulence of the extracellular pathogen Streptococcus agalactiae was investigated. We demonstrate that a DltA– isogenic mutant displays an increased susceptibility to host defence peptides such as human defensins and animal‐derived cationic peptides. Accordingly, the mutant strain is more susceptible to killing by mice bone marrow‐derived macrophages and human neutrophils than the wild‐type strain. In addition, the virulence of the DltA– mutant is severely impaired in mouse and neonatal rat models. This mutant was eliminated more rapidly than the wild‐type strain from the lung of three‐week‐old mice inoculated intranasally and, consequently, is unable to induce a pneumonia. Finally, after intravenous injection of three‐week‐old mice, the survival of the DltA– mutant is markedly reduced in the blood in comparison to that of the wild‐type strain. We hypothesize that the decreased virulence of the DltA– mutant is a consequence of its increased susceptibility to cationic antimicrobial peptides and to killing by phagocytes. These results demonstrate that the D‐alanylation of LTA contributes to the virulence of S. agalactiae.