DETECTION OF GENOMIC HETEROGENEITY IN STREPTOCOCCUS-SUIS ISOLATES BY DNA RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS OF RIBOSOMAL-RNA GENES (RIBOTYPING)

Whole-cell chromosomal digests of 54 isolates of Streptococcus suis encompassing all known serotypes from a geographically varied collection were examined by PstI restriction fragment length polymorphisms and then hybridized with a digoxigenin-11-dUTP-labeled cDNA probe transcribed from a mixture of 16S and 23S rRNAs from Escherichia coli MRE600. The hybridization patterns showed genetic heterogeneity within and between S. suis serotypes. Most isolates (87%) representing 28 serotypes contained a common band at similar to 1.8 kb. However, 13% of the isolates representing seven serotypes lacked the 1.8-kb band, indicating that the species as currently defined is diverse. Nonetheless, the 1.8-kb band may be a useful genotypic marker for identification of most S. suis isolates. We tested the ability of this technique to discriminate between virulent and avirulent S. suis type 2 isolates. A virulent strain of S. suis type 2 could be distinguished from avirulent strains by the presence of specific bands. No correlation was obvious between band pattern and hemolysin production.