Distribution of Environmentally Regulated Genes of Streptococcus suis Serotype 2 among S. suis Serotypes and Other Organisms

The occurrence of 36 environmentally regulated genes of Streptococcus suis strain 10 among all 35 S. suis serotypes was determined by using hybridization with the amplified genes as probes. In addition, the distribution of these genes among the virulence phenotypes of serotypes 1 and 2 was assessed. Hybridization was also performed with various other streptococcal species and nonstreptococcal bacterial species which may be present in pigs. Interestingly, probe ivs-25/iri-1, similar to agrA and sapR, hybridized only with S. suis serotype 1 and 2 strains with virulent phenotypes and is therefore suitable as a diagnostic parameter. Only one probe was specific for S. suis. This probe's sequence was identical to the epf gene, a putative virulence factor of S. suis. Probe ivs-31 was similar to a virulence factor of S. suis, namely, a gene encoding a fibronectin- and fibrinogen-binding protein. This probe hybridized only with oral streptococci. Nearly half of the probes (45%) hybridized with the oral streptococci (S. oralis, S. milleri, S. sanguis, S. gordonii, and S. mitis) and with Streptococcus pneumoniae. This indicates a close relationship between S. suis, the oral streptococci, and S. pneumoniae with respect to the selected environmentally regulated genes. One probe only hybridized with gram-negative species and therefore seems to be obtained by S. suis from a gram-negative organism by horizontal transfer.