Genetic diversity of Streptococcus suis isolated from pigs and humans in Chiang Mai and Lamphun province, Thailand

Streptococcus suis is recognized worldwide as an important swine pathogen, which occasionally infects humans and causes fatal illness. Seventy-three isolates of S. suis from patients and healthy pigs in Thailand were characterized by serotyping, three putative virulence genes (mrp, epf, and sly) and pulsed-field gel electrophoresis (PFGE). Of the 73 isolates, 63 human and 6 pig isolates were serotype 2, and 2 human isolates were serotype 1, and the remaining 2 human isolates were serotype 1/2. The 3 genes (mrp, epf, and sly) were detected in the 73 isolates by polymerase chain reaction (PCR) and 7 different genotypes were obtained. Interestingly, 2 genotypes from the healthy pig isolates corresponded to genotypes of human isolates (mrp+epf−sly− and mrp−epf−sly+). To characterize more discriminatorily, the 73 isolates were then analyzed by PFGE, and they were divided into 36 PFGE patterns (12 pulsotypes and 24 single patterns). These results indicated a great genetic diversity among S. suis isolates from humans and pigs. However, one pulsotype contained 8 isolates from humans and 4 isolates from pigs belong to the same pulsotype, suggesting a transmission of S. suis from pigs to humans.