Detection of virulent strains of Streptococcus suis type 2 and highly virulent strains of Streptococcus suis type 1 in tonsillar specimens of pigs byPCR

We developed a PCR assay for the rapid and sensitive detection of virulent Streptococcus suis type 2 and highly virulent S, suis type 1 in tonsillar s pecimens from pigs. The PCR primers were based on the sequence of the gene encoding the EF-protein of virulent S. suis type 2 strains (MRP+EF+) and hi ghly virulent S. suis type 1 strains ((MRPEF+)-E-s) and of the EF protein o f weakly virulent S. suis type 2 strains ((MRP+EF*)). The latter strains gi ve rise to larger PCR products than the virulent strains of S. suis type 1 and 2. A positive control template was included in the assay to identify fa lse negative results. The PCR was evaluated using tonsillar specimens from herds known (or suspected) to be infected and herds without an S. suis hist ory. The results obtained with the PCR assay were compared with the results obtained with a newly developed bacteriological examination. In this bacte riological examination we were able to identify the EF-positive strains dir ectly in the tonsillar specimens. From the 99 tonsils examined, 48 were pos itive in the PCR and 51 negative. All specimens from which EF-positive S, s uis strains were isolated were also positive in the PCR assay. Three sample s were positive in the PCR, but negative by bacteriological examination. Th e results demonstrated that the PCR is a highly specific and sensitive diag nostic tool for the detection of pigs carrying virulent strains of S. ntis type 2 and highly virulent strains of type 1. Application of the assay may contribute to the control of S. suis infections. (C) 1999 Elsevier Science B.V. All rights reserved.