EFFICACY OF INTRAPERITONEAL AND IMMERSION VACCINATION AGAINST ENTEROCOCCUS SP, INFECTION IN TURBOT

In this study the effectiveness of a toxoid-enriched whole-cell bacterin (ET-2) in cultured turbot (Scophthalmus maximus) against Enterococcus sp. was evaluated by bath immersion and intraperitoneal (i.p.) injection. In addition, the influences of fish size as well as enrichment of the standard semimoist diet with the commercial preparation Trouvitol plus(R), which contains beta-glucan from yeast, were also investigated. Regardless of fish size, type of diet, and bacterial dose employed in the experimental challenges, our Enterococcus bacterin ET-2 proved to be very effective when it was delivered by injection. The RPS (relative percent of survival) values achieved by this route ranged from 89 to 100 (for 45-g turbot) and from 67 to 86 (for 150-g turbot), depending on the bacterial levels and time of experimental challenge. Moreover, this strong degree of protection lasted for at least 1 year. No circulating antibodies were detected in the vaccinated turbot. However, the injected bacterin, irrespective of the diet utilized, elicited a significant (P < 0.01) increase of the phagocytic activity in the spleen. Although the glucan alone also induced an enhancement of the non-specific defence mechanisms, this stimulation was not correlated with the protection of turbot against Enterococcus infection.