Rapid identification of Streptococcus iniae by specific PCR assay utilizing genetic markers in ITS rDNA

The 16S-23S intergenic spacers (ITS) of ribosomal DNA from ten independent isolates of Streptococcus iniae and one reference strain ATCC29178 were sequenced, aligned and used to design a polymerase chain reaction (PCR) primer set for rapid and specific detection and identification of S. iniae. This primer set amplified a 377-bp DNA fragment specifically from S. iniae, but not from other common bacterial pathogens of fish or from non-fish pathogens. The PCR conditions were optimized to allow detection of the organism from agar, broth culture or infected fish tissue. The sensitivity of the PCR assay was established by the detection of DNA as low as 0.02 ng or as few as 10 CFU bacterial cells. The establishment of the specific PCR assay provides a useful tool for the identification and diagnosis of fish infection with S. iniae.