Construction And Characteristic Of SntA Gene Deleted Mutant Strain Of Streptococcus Suis Serotype 2

Streptococcus suis is one of the most important swine pathogens. Based on the CPS antigens of S. Suis,33 serotypes (types 1-31,33 and 1/2)have been characterized. Streptococcus suis serotype 2(SS2) is the most commonly and most virulent of these serotypes. SS2 is an zoonotic agent, which is responsible for severe economic losses to the porcine industry, moreover, SS2 is the causative agent of serious infections in humans. Recently, in the study of the virulence of various pathogens and the immune protective antigen protein, secreted proteins and membrane proteins become to the focus. Currently, the membrane surface protein which is cleaved and catalyzed the transfer to cell wall by sortase attract moer attention, almost all gram-positive bacteria have a similar mechanism of protein anchored to the cell wall. These cell wall surface protein are covalently anchored to the cell wall by a mechanism that requiring a C-terminal anchoring motif, which constitute of a conserved amino acid sequence, Leu-Pro-X-Thr-Gly(LPXTG, where X is any amino acid). According to the previous literature, SS2 SntA is a membrane protein. Except the C-terminal motif, LPXTG, SntA protein contain another amino acid motif, a tripeptide RGD. The RGD motif binds to integrins of mammalian cells. Integrins are heterodimeric membrane proteins located on the surface of mammalian cells that participate in cell to cell adhesion and cellular differentiation, migration, and attachment to the extracellular matrix. The SntA protein may directly bind integrin and participate in host-pathogen interactions. That is, SntA may be one of the virulence factor of SS2. Thus, we investigate the function of sntA gene in SS2 in this article.The project constructed the sntA gene deletion mutant strain(△sntA) of SS2 using plasmit pSET4s successfully. Compared the growth characteristics between△sntA and the wild strain, we found that the growth of two strains are similar in the logarithmic growth phase, and when△sntA grow into the plateau phase, the wild strain still in the logarithmic growth. Thus,△sntA limit the accumulation of bacteria quantity. Compared the colonization of△sntA and the wild strain in mice, we found that the colonization time of△sntA was longer, the anti-clear ability of△sntA has increased. Hep-2 cells as a model to study the different cell adhesion properties between△sntA and the wild atrain, via flow cytometry analysis, the results show that sntA gene deletion mutant's capacity of the adhesion to Hep-2 cells is similar to the wild strain, and inactivated the sntA gene can't alter the cellular adhesion ability. Compared the virulence of AsntA and the wild strain to the Balb/c mice, the outcome expressed that△sntA has a certain degree of decline, the LD50 value was 5×108CFU for△sntA, and the LD50 value of the wild strain was 2.5×108CFU.△sntA was attenuated at least two fold. Balb/c mice as a model to compared the immunity protective of SntA protein and the inactivated vaccine of SS2, the results indicate that SntA protein has a certain immune protection on the Balb/c mice, but it not as good as the protection of the inactivated vaccine of SS2.