Pathogenicity of a Strain of Streptococcus suis Type 2 to Mice and Swine Isolated from Jingzhou City

Aims: The objective of this study is to identify S. suis type 2 and evaluate the virulence of ZHJ01 strain isolation, and verity the clinical and pathological outcome of a systemic infection caused by one serotype 2 when simultaneously inoculated with ZHJ01 strain. We also want to clarify the epidemiologic, clinical, microbiologic characteristics and the pathogenesis mechanism of S. suis type 2 in Hubei province, China.

Study Design: Pigs suspected of being infected with S. suis in Jingzhou regions of Hubei province, China were studied. S. suis type 2 isolation was obtained from the suspicion of diseased pig. The case of S. suis type 2 was detected by the virulence factor amplification based on PCR detection and bacterial isolation, identification in the laboratory. According to the experimental infections of mice and piglets, pathogenicity of this S. suis type 2 isolation to mice and swine was monitored. This study was conducted in the key laboratory of pathogenic microbiology, College of Animal Science of Yangtze University, and Institute of Black Pigs Research, Yangtze University.

Methodology: Proper serological typing can be performed using a co-agglutination test. The typical colonies purificated and cultured were inoculated with Glucose, Lactose, Raffinos, Sorbitol, D (+)-sucrose, Trehalose, 6.5%NaCl, D (-)-Salicin, Hippurate, Esculin hydrate, V-p, etc., then the test results were recorded. Detection of virulence factors were performed using PCR amplification and DNA sequencing. S.suis type 2 isolation was inoculated to mice and piglets for the virulence test, and the observation of the clinical signs and pathological changes.

Results: The virulence factor of extracellular protein factor (EF) was determined from ZHJ01 strain based on PCR detection. Sequence analysis indicated that the isolate was very similar to nucleotide homology with others SS2 strains from different county or contries, and there was not much variation. LD50 of S. suis type 2 for mice was 2.5 x 107cfu. LD50 of S. suis type 2 for piglets was 3.92 x 109cfu.

Conclusion: The results show that Swine S. suis type 2 has a relatively strong pathogenicity to pigs in Hubei province, China. This study can be, in part, sufficient to explain the pathogenicity for ZHJ01 strain in area of Zhijing, Jingzhou city, China, which may provide insights into the pathogenesis SS2 and more valid data to support the development of S. suis vaccine as well as the epidemiological investigation, further monitoring and effective prevention to S. suis.