Carrier rate of Streptococcus suis capsular type 2 in palatine tonsils of slaughtered pigs.

Palatine tonsils of 143 slaughtered pigs aged 4 to 6 months were investigated for the presence of Streptococcus suis type 2. Slices (50 micron) of frozen tonsils were cultured on a selective agar medium containing antibodies against S. suis type 2 in which colonies of this bacterium showed a halo of immunoprecipitation. When tonsils were sectioned in one plane S. suis type 2 was found in 45 of 143 pigs (32%). This percentage increased to 50% when tonsils were sectioned in more then one plane, which was done on 55 tonsils. The first 45 strains showing a ring of immunoprecipitation were studied and found to be biochemically identical to our reference strain 735 (de Moor) and to 23 isolates from human patients with meningitis. In slices incubated for 24 h at 37 degrees C on selective agar plates and stained with hematoxylin and eosin after fixation, it could be demonstrated that S. suis type 2 was confined to the crypt lumen. The same was true in sections fixed directly (without incubation) that were stained by an indirect immunoperoxidase method with a rabbit anti-S. suis type 2 serum.