National Institute of Animal Health (NIAH)

Topics in Animal Health Research 2008

20. Type-1 serum opacity factor may contribute to the virulence of the limited members of Streptococcus suis

Japanese

  The serum opacity factor of Streptococcus suis (OFS) is a virulence determinant of an S. suis strain. We investigated the prevalence and variations of the ofs gene among 108 S. suis isolates from pigs and humans. PCR screening and sequencing analysis showed that there were four allelic variants of ofs (designated types 1 to 4). Type-1 and type-2 ofs coded functional OFS, and SDS extracts of the isolates with type-1 ofs and type-2 ofs opacified horse serum. In contrast, type-3 ofs was interrupted by point mutation, and type-4 ofs was disrupted by either insertion of an IS element or genetic rearrangement, and therefore the SDS extracts of the isolates with type-3 ofs and type-4 ofs did not show serum opacification activity. Regardless of their origins, approximately 30% of the isolates possessed functional OFSs, although type-2 ofs was found only in three isolates from healthy pigs. Multilocus sequence typing analysis showed that most of the isolates with type-1 ofs belonged to the sequence type (ST) 1 complex, and most of the isolates with type-3 ofs and type-4 ofs belonged to the ST27 complex. The isolates with type-2 ofs were not assigned to a major ST complex. These results suggest that type-1 OFS contributes to the virulence of the limited members of S. suis, i.e., those of the ST1 complex.
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Reference:

Takamatsu, D., et al. (2008) J. Med. Microbiol. 57: 488-494.

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