Non-destructive Molecular Detection of Streptococcus agalactiae in Rainbow Trout (Oncorhynchus mykiss)

The objective of this study was to evaluate a non-lethal sampling technique to detect Streptococcus agalactiae, the bacterial pathogen causing Streptococcosis, in the blood and mucus of the infected rainbow trout, Oncorhynchus mykiss. Detection was established by PCR protocol based on the scpB gene. Also biochemical identification method was set by API strepsystem and conventional bacteriological tests. The fish were infected by intraperitoneally (i.p.) with 8×107 CFU/ml colony forming units of S. agalactiae. The PCR and biochemical method were positive for the blood samples from 3th and 4th days after exposure up to the end of the experiment while the fish look healthy. Mucus samples in PCR assay and biochemical methods were not positive until the end of the experiment. All any biochemically positive results were positive in PCR protocol, but some PCR positive results were negative in biochemical method. PCR Sensitivity tests were done in fish tissues seeded with serial dilutions of pure culture of S. agalactiae. Mucus was not efficient when the bacteria count is low. This study revealed that a nonlethal blood sampling can be used with high efficiency primers for PCR protocol to detect S. agalactiae in asymptomatic fish.