Protective effects of chicken egg yolk antibody (IgY) against experimental Vibrio splendidus infection in the sea cucumber (Apostichopus japonicus)

• Intraperitoneal injection or immersion with specific IgY improved the survival of Vibrio splendidus-infected sea cucumber.
• Specific IgY decreased the bacterial burden in immune tissues and coelomic liquid.
• Specific IgY enhanced the phagocytosis of coelomocytes for V. splendidus.
• Specific IgY has potential for protecting sea cucumbers against skin ulceration syndrome.

Vibrio splendidus is one of the most harmful pathogens associated with skin ulceration syndrome in the sea cucumber (Apostichopus japonicus) due to its high virulence and frequency of appearance. The objective of this study was to determine the effectiveness of chicken egg yolk antibody (IgY) against V. splendidus infection in the sea cucumber. Whole V. splendidus cells were used as an immunogen to immunize 20 White Leghorn hens (25 weeks old). IgY was produced from egg yolks obtained from these immunized hens using water dilution, two-step salt precipitation and ultrafiltration. The purity of the IgY produced was approximately 83%. Enzyme-linked Immunosorbent Assay indicated a high specificity for IgY with a maximum antibody titer of 320,000. The growth of V. splendidus in liquid medium was significantly inhibited by IgY in a dose-dependent manner at concentrations ranging from 1 to 10 mg/mL. The protective effects of IgY were evaluated in sea cucumber by intraperitoneally injecting anti-V. splendidus IgY antibodies (10 mg/mL) or immersing the sea cucumber in aqueous IgY (1 g/L) after an intraperitoneal injection of V. splendidus. Intraperitoneal injection resulted in an 80% survival while immersion resulted in a 75% survival during the 11-day experimental period. The survival rates were significantly higher than the positive control and the non-specific IgY group (P < 0.05). As well, the bacterial burden in the respiratory tree, intestine and coelomic liquid was significantly (P < 0.05) lower in sea cucumber treated with specific IgY than those treated with non-specific IgY. The phagocytosis of coelomocytes for V. splendidus in the presence of specific IgY was significantly (P < 0.05) higher than that obtained with non-specific IgY or without IgY, suggesting that specific IgY enhanced phagocytic activity. The current work suggests that specific IgY has potential for protecting sea cucumbers against V. splendidus infection.