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Title: Protection against heterologous Streptococcus iniae isolates using a modified bacterin vaccine in Nile tilapia Oreochromis niloticus

item Shoemaker, Craig
item Klesius, Phillip
item Lafrentz, Benjamin
item Evans, Joyce

Submitted to: European Association of Fish Pathologists
Publication Type: Abstract Only
Publication Acceptance Date: 6/18/2009
Publication Date: 9/14/2009
Citation: Shoemaker, C.A., Klesius, P.H., Lafrentz, B.R., Evans, J.J. 2009. Protection against heterologous Streptococcus iniae isolates using a modified bacterin vaccine in Nile tilapia Oreochromis niloticus. 14th European Association of Fish Pathologists. International Conference Prague, Czech Republic September 14-19, 2009. p. 98.

Interpretive Summary:

Technical Abstract: Streptococcus iniae is an important pathogen of both wild and cultured fish worldwide. Losses are estimated in the hundreds of million dollars annually in cultured fish. The objectives of this study were to determine if a developed modified S. iniae bacterin vaccine was efficacious against heterologous isolates and to evaluate protein and antigenic variability among the isolates tested. The calcein cohabitation challenge system was used to test the developed vaccine’s (ARS-60) ability to protect against four isolates from diverse geographic locations. The isolates were acquired from farm outbreaks. Tilapia were intraperitoneally (ip) immunized with 100 µl of the vaccine and held for 28 days. Prior to challenge (72 h), sham immunized fish (sterile tryptic soy broth 100 µL) were marked with calcein. Fish (~15 g) were challenged by ip injection of about 10 million CFU / fish and mixed into 4 replicate tanks containing (10 immunized and 10 sham immunized). Paired T-tests demonstrated significant protection (P<0.05) against all challenge isolates. Relative percent survival ranged from 78 to 100 %. SDA-Page analysis of the isolates demonstrated similar protein profiles between 10 and 35 kDa with some variability in staining intensity of bands. Larger sized protein bands (37 to 100 kDa) showed considerable variability. Western blot analysis using antiserum from vaccinated fish (ARS-60) demonstrated shared immunogenic proteins among all isolates in the molecular mass range of 22-35 KDa and high molecular mass bands > 150 kDa. Considerable variability was seen between 37 and 75 kDa depending on isolate. The results suggest that the developed S. iniae vaccine may have broad ranging protection and further studies are underway to evaluate more isolates using the described challenge system.