Establishment and application of duplex PCR assay for detection of Streptococcus suis species and serotype 9.

A duplex PCR assay for detection of Streptococcus suis (SS) species and Serotypes 9 (SS9) was developed using the primers designed based on the gene encoding glutamate dehydrogenase (gdh) of S. suis and cps9H gene encoding the capsule (cps) of S. suis serotypes 9 (SS9) . The DNA of standard SS9 strain was used as the positive control to establish the duplex PCR assay. The sensitivity, specificity and repetition of the PCR assay were tested, and 34 purified culture samples taken from clinic suspicious S.suis infected pigs were detected by the established duplex PCR assay in contrast to the routine bacterial isolation and identifying method. The results indicated the duplex PCR assay were successfully established. The specificity and the sensitivity of the duplex PCR assay revealed that the duplex PCR threshold was 100 CFU of S. suis, and no products were amplified from the genomic DNA of the other 6 pathogenic bacterial acting as the negative control. The repetition test indicated that the duplex PCR was reproducible. Total 11 of 34 purified strains suspicious Streptococcus infected of culture samples demonstrated the gdh positive, which was consistent with the results of the routine bacterial isolation and identifying method, and 3 of 11 gdh positive samples displayed the cps9H positive, too. Our study suggested that the established duplex PCR method was highly specific and sensitive,and was suited to clinic rapid diagnosing of Streptococcus suis species and Serotypes 9.