Streptococcus suis serotypes characterized by analysis of chaperonin 60 gene sequences

Streptococcus suis is an important pathogen of swine which occasionally inf ects humans as well. There are 35 serotypes known for this organism, and it would be desirable to develop rapid methods methods to identify and differ entiate the strains of this species. To that effect, partial chaperonin 60 gene sequences were determined for the 35 serotype reference strains of S. suis. Analysis of a pairwise distance matrix showed that the distances rang ed from 0 to 0.275 when values were calculated by the maximum-likelihood me thod. For five of the strains the distances from serotype I were greater th an 0.1, and for two of these strains the distances were were more than 0.25 , suggesting that they belong to a different species. Most of the nucleotid e differences were silent; alignment of protein sequences showed that there were only 11 distinct sequences for the 35 strains under study. The chaper onin 60 gene phylogenetic tree was similar to the previously published tree based on 16S rRNA sequences, and it was also observed that strains with id entical chaperonin 60 gene sequences tended to have identical 16S rRNA sequ ences. The chaperonin 60 gene sequences provided a higher level of discrimi nation between serotypes than the 16S RNA sequences provided and could form the basis for a diagnostic protocol.