Isolation of Streptococcus suis type 2 from healthy pigs in Ziyang district of Sichuan province and analysis of their molecular characteristics

To investigate the carrying status of Streptococcus suis,the distribution of virulence genes and the antibiotics susceptibility of the isolates in healthy pigs in Ziyang district,Sichuan province,and to analyze the homology between isolates from pigs and those isolated from human patients,so as to provide a basis for outbreak prediction and preventive measures,all strains of Streptococcus were isolated from samples of nasopharyngeal swabs and tonsils collected from healthy pigs,biochemically identified with API 20 Strep kit and serologically typed with specific diagnostic sera for S.suis.Polymerase chain reaction(PCR) was used to detect the presence of their specific gene 16S rDNA and the virulence-related genes.The antibiotics susceptibility of the isolates was determined by K-B paper disc method and the the homology between isolates from pigs and human patients was analyzed by pulse-field gel electrophoresis(PFGE).It was found that 12 strains of S.suis were isolated from healthy pigs and all the isolates were proved serologically to be type 2.All the isolates carried virulence genes,such as cps2J,mrp,sly,ef and gapdh and had the same antibiotics susceptibility spectrum.As demonstrated by PFGE pattern,the isolates from pigs were indistinguishable with those from human patients during the same time.From these observation,it is concluded that the strains of S.suis isolated from healthy pigs in Ziyang district of Sichuan province are proved to be highly pathogenic and highly homologous to those strains isolated from human patients.However,the occurrence of S.suis type 2 in healthy pigs shows seasonal disparity.