Gene ss-1616 is a conserved hypothetical outer membrane protein in SS2 genome database, and almost nothing is known about this gene.

It was found in all tested strains in this study, and in Canada strain 89/1591 and European strain P1/7. Many surface proteins of pathogenic gram-positive bacteria are linked to the cell wall envelope by a sorting mechanism that recognizes an LPXTG motif, but surface proteins of Streptococcus pneumoniae harbor another motif, YSIRK-G/S [42]. this website About 20 surface proteins of Staphylococcus aureus carry the YSIRK-G/S motif, whereas those of Listeria monocytogenes and Bacillus anthracis do not [43, 44]. While the function of the YSIRK motif has not been completely Cisplatin mouse elucidated, it may contribute to the efficient secretion of a protein [43]. In the present study, four clones encoded two proteins containing this motif. Although the gene ysirk was only detected 12 h after SS2 infection and then disappeared, and was not strongly upregulated in vivo, the mature protein encoded by ysirk1 showed homology to the surface-associated subtilisin-like serine protease PrtA (a virulence factor)

of S. pneumoniae[21]. However, the role of this protein during SS2 infection remains to be determined. IVIAT enables the identification both of proteins expressed specifically during host infection but not during growth under standard laboratory conditions, and of proteins expressed at significantly higher levels in vivo than in vitro. But IVIAT has its own limitations. IVIAT will not identify all virulence-associated genes. Genes that are expressed both in vivo and in vitro and genes that are not expressed effectively in the E. coli host expression system will not be identified. For instance, some previously reported SS2 virulence factors, such as MRP,

EF, FBPs, CPS, and SLY, could not be screened out by IVIAT in this study. We speculate that they are expressed in both in vivo and in vitro growth conditions, and therefore antibodies specific to these antigens had been eliminated during the convalescent sera adsorption steps. Unexpectedly, some of the genes identified are likely expressed during in vitro growth conditions, such as DNA polymerase I and III, Primosomal protein much n, protein Cpn60, and SMC protein (essential for bacterial cell division and cell wall biosynthesis). We speculate that perhaps their expression level was higher during in vivo growth than in vitro growth, and therefore they were detected by the IVIAT. Conclusion Taken together, our results suggest that during the course of infection, bacterial metabolism, envelope composition, and virulence will be adjusted for bacteria to survive in the hostile environment. Bacterial pathogens sense their environment, and in response, genes are induced or repressed through spatial and temporal regulation.