Innate immunity and protective immune responses in yellowtail induced by liposome-type Lactococcus garvieae vaccine

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Intensive fish farming has become a key industry in recent decades. With the increasing scale of aquaculture, fish are now reared at high population densities. Mass mortality occurs if infectious agents are introduced into the farm, causing great financial loss. Difficulty in control of disease arises from the limited effectiveness of chemotherapy, and from asymptomatic carriage of the disease, leading to outbreaks of disease when affected fish stocks are stressed. Lactococcus garvieae infection in the yellowtail is a prevalent bacterial disease in Japan. The mucosal tissues of the body of fish constitute an enormous surface area, and many infectious organisms invade through or colonise mucosal tissues, especially the intestinal tract. These pathogens recognize the carbohydrate structure on the surface of cells as a receptor for binding. Glycosphingolipids (GSL) are ubiquitous components of the plasma membrane of cells. The present study was undertaken to demonstrate the adherence of L.garvieae to GSL of the yellowtail. Lactococcus garvieae adhered to ganglioside bands purified from the intestinal mucous membrane and brain having similar mobility to GM_3 ganglioside standard, according to thin layer chromatography. Adherence of the bacteria was blocked by pretreatment of the intestinal tract preparation with glycosidase in a dose-dependent manner, implying indicating that ganglioside acts as a binding receptor of L.garvieae in the yellowtail intestinal tract.