Abstract: A multiplex PCR assay for detection Streptococcus suis (S. suis, SS) serotypes 1, 7, 9 (SS1, SS7, SS9) was developed using the primers designed basing on the gene coding for CPS1I, CPS7H and CPS9H coding for the capsule (CPS) of SS1, SS7 and SS9, respectively. The DNA of standard SS1, SS7 and SS9 strains were used as the positive control to establish the multiplex PCR assay. The sensitivity, specificity and repetition assay of multiplex PCR were tested, and 11 purified S. suis strains of culture samples taken from clinic suspicious S. suis infected pigs and having been testified by routine bacterial isolating and identification were detected by the established multiplex PCR assay. The results indicated that the multiplex PCR assay was successfully established. The specificity and the sensitivity of the multiplex PCR assay revealed that the multiplex PCR threshold was 100 CFU/mL of S. suis, and no products were amplified from the genomic DNA of the standard SS2 strain and the other 6 kinds of pathogenic bacterial microorganism acting as the negative control. The repetition test indicated that the duplex PCR was repeatable. Total 3, 2, 1 of 11 purified S. suis strains of culture samples displied the CPS9H, CPS7H, CPS1I positive, respectively. The results showed that the established multiplex PCR method was highly specific and sensitive，and was suited to clinic rapid diagnosing of S. suis serotypes1, 7 and 9.

Key words: Streptococcus suis; serotypes 1; multiplex PCR; detection; establishment; application