Surface-associated lipoprotein PpmA of Streptococcus pneumoniae is involved in colonization in a strain-specific manner

Abstract

Streptococcus pneumoniae produces two surface-associated lipoproteins that share homology with two distinct families of peptidyl-prolyl isomerases (PPIases), the streptococcal lipoprotein rotamase A (SlrA) and the putative proteinase maturation protein A (PpmA). Previously, we have demonstrated that SlrA has PPIase activity, and that the enzyme plays a role in pneumococcal virulence. Here, we investigated the contribution of PpmA to pneumococcal pathogenesis. Pneumococcal mutants of D39 and TIGR4 lacking the gene encoding PpmA were less capable of persisting in the nasopharynx of mice, demonstrating the contribution of PpmA to pneumococcal colonization. This observation was partially confirmed in vitro, as the pneumococcal mutants NCTC10319DeltappmA and TIGR4DeltacpsDeltappmA, but not D39DeltacpsDeltappmA, were impaired in adherence to Detroit 562 pharyngeal cells. This suggests that the contribution of PpmA to pneumococcal colonization is not solely the result of its role in adherence to epithelial cells. Deficiency in PpmA did not result in reduced binding to various extracellular matrix and serum proteins. Similar to SlrA, we observed that PpmA was involved in immune evasion. Uptake of PpmA-deficient D39Deltacps and NCTC10319 by human polymorphonuclear leukocytes was significantly enhanced compared to the isogenic wild-types. In addition, ingestion of D39DeltappmA, but not that of either NCTC10319DeltappmA or TIGR4DeltappmA, by murine macrophage cell line J774 was also enhanced, whereas intracellular killing remained unaffected. We conclude that PpmA contributes to the early stages of infection, i.e. colonization. The contribution of PpmA to virulence can be explained by its strain-specific role in adherence to epithelial cells and contribution to the evasion of phagocytosis.