Enhancement of disease resistance of kuruma shrimp, Penaeus japonicus, after oral administration of peptidoglycan derived from Bifidobacterium thermophilum

The potency of oral administration of peptidoglycan (PG) derived from Bifidobacterium thermophilum was examined. PG was administered to kuruma shrimps through the diet at 0.2 mg/kg body weight/day for 7 consecutive days, alternated with 7 days without PG throughout a 95-day test period. The shrimps were sampled on day 65 and 95 and challenged by Vibrio penaeicida, which is highly virulent to shrimps, through a water-borne route. The survival rate of PG-fed group was significantly higher than the control (P < 0.01). PG-fed shrimps were challenged by white spot syndrome baculovirus, The survival rate was significantly higher than the control (P < 0.01). To clarify the mechanism of defense that was enhanced by oral administration of PG, the phagocytic activity of shrimp granulocytes in vitro expressed by the phagocytic index (PI) was examined. Granulocytes were obtained from shrimps fed with PG and isolated by Percoll continuous density gradient. Fluorescently-labeled latex beads were used for the phagocytosis assay. The PI of PG-fed shrimps was higher than that of the control (P < 0.05). These results indicate that the oral administration of PG to kuruma shrimp enhances the phagocytic activity of the granulocytes and increases the disease resistance of shrimps. (C) 1998 Elsevier Science B.V. All rights reserved.