Lipoproteins in Staphylococcus aureus Mediate Inflammation by TLR2 and Iron-Dependent Growth In Vivo

Lipoproteins (Lpp) are ligands of TLR2 and signal by the adaptor MyD88. As part of the bacterial cell envelope, Lpp are mainly involved in nutrient acquisition for Staphylococcus aureus. The impact of Lpp on TLR2-MyD88 activation for S. aureus in systemic infection is unknown. S. aureus strain SA113 deficient in the enzyme encoded by the prolipoprotein diacylglyceryl transferase gene (Deltalgt), which attaches the lipid anchor to pro-Lpp, was used to study benefits and costs of Lpp maturation. Lpp in S. aureus induced early and strong cytokines by TLR2-MyD88 signaling in murine peritoneal macrophages. Lpp contributed via TLR2 to pathogenesis of sepsis in C57BL/6 mice with IL-1beta, chemokine-mediated inflammation, and high bacterial numbers. In the absence of MyD88-mediated inflammation, Lpp allowed bacterial clearing from liver devoid of infiltrating cells, but still conferred a strong growth advantage in mice, which was shown to rely on iron uptake and storage in vitro and in vivo. With iron-restricted bacteria, the Lpp-related growth advantage was evident in infection of MyD88(-/-), but not of C57BL/6, mice. On the other hand, iron overload of the host restored the growth deficit of Deltalgt in MyD88(-/-), but not in immunocompetent C57BL/6 mice. These results indicate that iron acquisition is improved by Lpp of S. aureus but is counteracted by inflammation. Thus, lipid anchoring is an evolutionary advantage for S. aureus to retain essential proteins for better survival in infection.