The VraSR two-component signal transduction system contributes to the damage of blood-brain barrier during Streptococcus suis meningitis.

Streptococcus suis (S. suis) is an important zoonotic pathogen that can cause high morbidity and mortality in both humans and swine. As the most important life-threatening infection of the central nervous system (CNS), meningitis is an important syndrome of S. suis infection. The vancomycin resistance associated sensor/regulator (VraSR) is a critical two-component signal transduction system that affects the ability of S. suis to resist the host innate immune system and promotes its ability to adhere to brain microvascular endothelial cells (BMECs). Prior work also found mice infected with ΔvraSR had no obvious neurological symptoms, unlike mice infected with wild-type SC19. Whether and how VraSR participates in the development of S. suis meningitis remains unknown. Here, we found ΔvraSR-infected mice did not show obvious meningitis, compared with wild-type SC19-infected mice. Moreover, the proinflammatory cytokines and chemokines in serum and brains of ΔvraSR-infected mice, including IL-6, TNF-α, MCP-1 and IFN-γ, were significantly lower than wild-type infected group. Besides, blood-brain barrier (BBB) permeability also confirmed that the mutant had lower ability to disrupt BBB. Furthermore, in vivo and in vitro experiments showed that SC19 could increase BBB permeability by downregulating tight junction (TJ) proteins such as ZO-1, ß-Catenin, Occludin, and Clauidn-5, compared with mutant ΔvraSR. These findings provide new insight into the influence of S. suis VraSR on BBB disruption during the pathogenic process of streptococcal meningitis, thereby offering potential targets for future preventative and therapeutic strategies against this disease.

[Construction and characteristics of a recombinant strain apx II C- /apx I A+ of Actinobacillus pleuropneumoniae serotype 7].

An Actinobacillus pleuropneumoniae apx II C mutant was constructed by transconjugation and counterselection method. Briefly, a transconjugation plasmid pEHA1 was constructed, and transformed into donor strain Escherichia coli 32155. After mixed the donor cells with A . pleuropneumoniae acceptor cells, the mixture was cultivated for about 5 hours and plated on solid medium containing chloromycetin. Then the Cm(R) positive clones were picked and inoculated into liquid medium in the absence of any antibiotic. Cultures were pelleted, plated on sucrose plates and incubated overnight. Finally, Sucrose-resistant colonies (Suc(R)) were selected and considered as mutant. The mutant was verified by PCR, heredity stability, exotoxin secretion and sequence analysis, suggested that the construction of the mutant was sucessful. The biological characteristics of this mutant strain was further investigated. Compared with parental strain, the results indicated that the mutant hold the same growth rate in vitro and reduced virulence on mice. Altogether, this mutation system will facilitate development of live attenuated vaccines and research on functions of novel genes of A. pleuropneumoniae.

[Study on immunogenicity of the N-terminal polypeptide of RTX toxin I of Actinobacillus pleuropneumoniae].

ApxI is one of the most important virulence factors of Actinobacillus pleuropneumoniae (APP). To study the immunogenicity of the ApxI, the complete coding sequence (3146bp) and its 5'-terminal 1140 bp fragment of the apxIA gene were separately cloned into the prokaryotic expression vector pET-28a, and expressed in the E. coli BL21 (DE3) with induction by IPTG. The expression products, rApxIA and rApxIAN, were present in a form of inclusion bodies and showed the same immunological reactivity as natural ApxI (nApxI) in Western-blot analysis. BALB/c mice were intraperitoneally immunized with the rApxIA, rApxIAN and nApxI respectively. The serum antibody levels of the rApxIAN immunized mice were significantly lower than those immunized with rApxIA or nApxI in an ApxI-specific ELISA, but serum neutralization test demonstrated that immunized mice with rApxIAN, rApxIA and nApxI could generate similar levels of antibodies neutralizing the hemolytic activity of the natural ApxI. The rApxIAN was able to elicite 80% protection rate against APP serovar 1 and 100% against serovar 2 when challenged at a dose of one LD50 after 2 weeks of boost immunization.