Effect of galangal (Alpinia galanga Linn.) extract on the expression of immune-related genes and Vibrio harveyi resistance in Pacific white shrimp (Litopenaeus vannamei)

Some plant and herb extracts reportedly possess antimicrobial activities and also have the ability to enhance the nonspecific immune system of shrimp, thereby promoting disease resistance. In this study, a natural herb, galangal (Alpinia galanga Linn.), was used to prevent infectious disease in cultured shrimp, and the effects of galangal-ethanol extract on the expression of the immune-related genes in the shrimp were analyzed via a reverse-transcription polymerase chain reaction of mRNA in circulating hemocytes. Following the intramuscular injection of either galangal extract or trans-p-coumaryl diacetate that had been isolated from galangal rhizome, Pacific white shrimp (Litopenaeus vannamei) showed significant increases in the relative expression ratio of the six immune-related genes compared with a control group. Furthermore, following the oral administration of galangal extract, similar inducible effects of the expression of immune-related genes in the Pacific white shrimp were obtained, which led to an enhanced survival rate from Vibrio harveyi infection. Thus, this study revealed that both galangal extract and trans-p-coumaryl diacetate stimulated the immune system response, thereby promoting resistance to V. harveyi infection in Pacific white shrimp.