Relatedness of Streptococcus suis isolates of various serotypes and clinical backgrounds as evaluated by macrorestriction analysis and expression of potential virulence traits

We evaluated the genetic diversity of Streptococcus suis isolates of differ ent serotypes by macrorestriction analysis and elucidated possible relation ships between the genetic background, expression of potential virulence tra its, and source of isolation. Virulence traits included expression of serot ype-specific polysaccharides, muramidase-released protein (MRP), extracellu lar protein factor (EF), hemolysin activity, and adherence to epithelial ce lls. Macrorestriction analysis of streptococcal DNA digested,vith restricti on enzymes SmaI and ApaI allowed differentiation of single isolates that co uld be assigned to four major clusters, named A1, A2, B1, and B2. Compariso n of the genotypic and phenotypic features of the isolates with their sourc e of isolation showed that (i) the S. suis population examined, which origi nated mainly from German pigs, exhibited a genetic diversity and phenotypic patterns comparable to those found for isolates from other European countr ies; (ii) certain phenotypic features, such as the presence of capsular ant igens of serotypes 2, 1, and 9, expression of MRP and EF, and hemolysin act ivity land in particular, combinations of these features), were strongly as sociated with the clinical background of meningitis and septicemia; and (ii i) isolates from pigs with meningitis and septicemia showed a significantly higher degree of genetic homogeneity compared to that for isolates from pi gs with pneumonia and healthy pigs. Since the former isolates are considere d highly virulent, this supports the theory of a clonal relationship among highly virulent strains.