Identification and characterization of Streptococcus suis serotype 2 isolated from diseased pigs in Ziyang area of Sichuan province

In summer of 2005,an outbreak of Streptococcus suis type 2 infections in animals and humans with deaths of hundreds of pigs and 38 human deaths was observed in Ziyang and adjacent area of Sichuan province. From the clinical samples of pigs died in this outbreak, 11 strains of Streptococcus suis type 2 were isolated, and these isolated strains were underwent identification by multiplex PCR and real-time PCR. It was found that all these 11 strains possessed 2 main virulence factors, i.e. muramidase released protein (MRP) gene and extracellular factor (EF) protein gene.Five of the 11 strains isolated from Sichuan and another strain isolated from Spain were compared for the susceptibility to antibiotics, in which all these 6 strains from Sichuan and Spain was found to be highly sensitive to amipicillin, cefoperazone, cefixime, acetylspiramycin, vancomycin, sinomin compositea and rifampicin.but in comparison with the Spanish isolate, the 5 strains of Sichuan were resistant to streptomycin.Meanwhile, all the tested strains showed different degree of pathogenicity to mice, in which both the strain 440-1 isolated from Sichuan and the isolate from Spain had high pathogenicity to mice (3/3 death), but the strain 458 isolated from Sichuan showed low pathogenicity to mice. ( 0/3 death).The death rates of rabbits inoculated with strain 449-1, 458 and 6 were 1/2, 2/2 and 2/2 respectively.In addition, we had obtained evidence of harboring the lysogenic phages in Stroptococcus suis type 2, but the relationship of this phage with the bacterial virulence and adaptation was uncertain.