D-Alanylation of Lipoteichoic Acid Contributes to the Virulence of Streptococcus suis

We generated by allelic replacement a dltA mutant of a virulent Streptococcus suis serotype 2 field strain and evaluated the contribution of lipoteichoic acid (LTA) D-alanylation to the virulence traits of this swine pathogen and zoonotic agent. The absence of LTA D-alanylation resulted in increased susceptibility to the action of cationic antimicrobial peptides. In addition, and in contrast to the wild-type strain, the dltA mutant was efficiently killed by porcine neutrophils and showed diminished adherence to and invasion of porcine brain microvascular endo-thelial cells. Finally, thedltAmutant was attenuated in both the CD1mouse and porcine models of infection, probably reflecting a decreased ability to escape immune clearance mechanisms and an impaired capacity to move across host barriers. The results of this study suggest that LTA D-alanylation is an important factor in S. suis virulence. Streptococcus suis is a major swine pathogen and a zoonotic agent that is responsible for, among other diseases, meningitis and septicemia (15). In swine, S. suis causes severe losses to the industry (15), while human S. suis infection is emerging as an important public health issue (13). Very recently, more than 200 cases of human S. suis infection were reported during an outbreak in China, and 38 of these cases resulted in death (39)