Identification Of Streptococcus Suis Serotype 2 Isolated From Swine And Pathological Research Of Experimental Pig Infected With Streptococcus Suis Serotype2

Streptococcus suis is an etiological agent of human, swine and animal infections. Thirty five major serotypes of Streptococcus suis have been described based on antigenic differences in the capsular polysacchairide(type 1/2 and 1 through 34). Among which Streptococcus suis type 2 is the most virulent and the most wide spread serotype. Streptococcus suis type 2 causes meningitis, arthritis, pericarditis, pneumonia and septicemia of piglets. Meniningitis is the most notable symptom. Out breaks of Streptococcus suis type 2 occurred in 1998 and 2005 in Jiangsu and Sichuan province were responsible for human infection and death. Dieases caused by this agent has generated huge economic losses. It is also a major threat to public heath and food safety. Streptococcus suis type 2 has become a major zoonosis agent, which attracts wide attention of many countries. In our country, researches on this diease mainly focus on epidemiology analysis, pathology analysis, development of vaccines and rapid diagnostic technologies. Systematic researches on pathology are comparatively few. One strain of Streptococcus suis was isolated from tissues of dead pigs of a pig farm in east China, and do some research on etiology. At the same time, systematic pathological research was developed after the piglets been injected with the Streptococcus suis type 2 (SSsc0501) isolated from Sichuan province.1. Isolation and identification of the Streptococcus suis type 2, cloning and sequence analysis of it's capsular polysaccharide 2J geneOne strain of Streptococcus suis was isolated from tissues of dead pigs. The bacteria was tested by Gram staining, agglutination test and PCR, at last, it was identificated to be Streptococcus suis type 2. Virulence factor targeted PCR generated positive results in MRP and EF. CPS2J gene of the bacteria was sequenced. Homology between sequences of this isolation and published sequences of Streptococcus suis type 2 were between 92.8% and 99.9%. Homology droped to 46.3% when it was compared with sequence of Streptococcus suis type 1.2. Pathological research of experimental piglets infected with Streptococcus suis type 2Ten 40-day-old healthy piglets were selected and experimentally infected with SSsc0501(one strain of Streptococcus suis type 2 isolated from Sichuan in 2005) by intramuscular injection. Pathological chances occurred in different tissues and organs were observed and researched. Results of this experiment showed that clinical symptoms occurred 22 hours after injection. Death occurred 48 hours after injection. This indicates this strain of Streptococcus suis type 2 is very virulent to piglets. This strain of Streptococcus suis 2 generally causes multi-organ septicimiapathology. Pathological changes occurred in liver were: hemorrhage, distortion of hepatic cord, congestion in central veins, swell, granular degeneration, fatty degeneration and vacular degeneration of liver cells. No notable pathological changes were observed in heart. Changes in spleen were several hemorrhage around central veins, reducing of lymphoid leucocytes, necrosis of some lymphoid leucocytes. Interstitial pneumoniae was observed, alveolar septum became wider, hemorrhage, exudation and necrosis was also observed. Pathological changes happened in kidney were: hemorrhage in medullar, renal glomerilus, atrophy of some renal glomerulus, swell and hemorrhage in renal capsule. Epithelium of nephric tubule began to ablate. Hemorrhage in lymphonode, necrosis of lymphoid leucocytes. Congestion and hyaline thrombus in veins were observed in brain. Pathological changes in intestine were generally bleeding and exudation with inflammatory cells.