| Streptococcus suis is a Gram-positive coccus that has been considered an important swine pathogen and a zoonotic agent causing meningitis, arthritis,septicaemia, pneumonia and even sudden death in swine and humans. So far,35different serotypes of S. suis have been described. Among them, serotype2is the most virulent and isolated from both diseased swine and humans frequently. There has been increasing numbers of studies on the virulence factors and pathogenesis of S. suis2, but the pathogenesis of SS2is not very clear by now. The S.suis2Egfp-HA9801recombinant with egfp and spcr gene, was constructed for pathogenesis studies as a EGFP labeled strain. However, firstly it is very significant to study on the biological, infection ttrends and fluorescence characteristics of the recombinant before using it on the SS2pathogenesis research.The biological characteristics were compared between the recombinant strain (Egfp-HA9801) and the wild strain (HA9801) by observing the characteristics of morphology, hemolysis, biochemistry, and the growth curve. The results showed that the biological characteristics of Egfp-HA9801were stable and similar to HA9801,and had not been clearly influenced by inserting egfp and spcr gene into SS2genome. So this study laid the foundation for using the EGFP labeled Egfp-HA9801on pathogenesis research.BALB/C mice were used as model animal to compare the characteristics of infection trends in infected animal between the S.suis2recombinant (Egfp-HA9801) and the wild strain (HA9801). The BALB/C mice were intraperitoneally inoculated with Egfp-HA9801and HA9801respectively which were diluted in sterile THB, and observed for clinical symptoms. Meanwhile, the numbers of dead mice within72hours were recorded and the dynamic curve of bacteria in different tissue also were drew according to the results of viable colony count. Finally, the bacteria isolated from the infected mice was also identified. All the infected mice had showed clear acute infectious symptoms and the inoculated bacteria could be isolated from the corresponding infected mice. Moreover, LD50of Egfp-HA9801and HA9801were3.200×108CFU and3.259×108CFU respectively and the dynamic curve of the two strains were extremely similar but no significant difference between them (P>0.05). The results also indicated that Egfp-HA9801was similar with HA9801for virulence, symptoms and infection process. Therefore, the recombinant strain can be used as EGFP labeled strain for SS2pathogenesis research under natural conditions.The fluorescence of Egfp-HA9801was detected initially with epifluorescence microscopy in this study. The bacteria cells grown at28℃,30℃and37℃for12h、24h、36h and48h were detected respectively. And the cryosections of the tissue, obtained from the dead BALB/C mice which were intraperitoneally inoculated with6.0×108CFU bacteria, were also detected. The results of this study indicated that the Egfp-HA9801cells grown at37℃for36hours showed more obvious green fluorescence than the others. Furthermore the tissue cryosections fluorescence of Egfp-HA9801-injected mice were also observed.In summary, Egfp-HA9801is extremely similar with HA9801on the characteristics of biological and infection trends, and the fluorescence of Egfp-HA9801is obvious and can be observed easily. Consequently, Egfp-HA9801can be used as a tracer on SS2pathogenesis research. |
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