餵食乳酸菌（Pediococcus pentosaceus）對於提升石斑免疫指標及病毒性疾病抵抗力之評估

Abstract

石斑魚為台灣重要的養殖魚種，幼苗期間常因神經壞死症病毒與虹彩病毒感染而大量死亡。益生菌可以用來提升魚的免疫力以控制疫情的發生。自海鱺腸道分離到的一株乳酸菌LAB 4012 (Pediococcus pentosaceus strain 4012) ，已證明經兩週餵食海鱺後，可提升週邊血球呼吸爆活性及對發光桿菌症之抵抗力 (刑, 2010) 。本實驗目的，在探討LAB 4012可否經由餵食，提高石斑魚免疫指標及抵抗病毒性疾病的能力。結果顯示，將餵食LAB 4012四週後的石斑苗進行虹彩病毒攻毒，其餵食組之存活率比對照組高出40%，且可提升石斑腸道及頭腎的C3及Mx基因表現。餵食LAB 4012一週及三週的石斑魚，血球呼吸爆與吞噬活性皆明顯提高，顯示LAB 4012能強化石斑魚先天免疫力。在餵食LAB 4012魚之腸道中可檢測到LAB 4012菌株的存在，證明LAB 4012能耐石斑魚胃酸及膽鹽而達腸道駐留。在體外實驗中，以LAB 4012培養後的上清液處理石斑魚細胞株GF-3，不會誘發Mx基因表現，但可降低虹彩病毒進入細胞的量，降幅約37%，推測是LAB 4012的代謝物中某些成份可阻斷GF-3細胞上的病毒受器，而降低病毒進入細胞的量。LAB 4012上清液在病毒複製階段中可降低NNV病毒RNA2基因複製的量。綜合上述結果，顯示乳酸菌LAB 4012具有潛力成為防治石斑魚病毒性疾病的益生菌。

Groupers (Epinephalus spp.) are important fish species for aquaculture in Taiwan. Viral pathogens, including nervous necrosis virus and grouper iridovirus (GIV) have caused mass mortality of grouper at larval and juvenile stage. Probiotics have potential to enhance fish immunity and antagonize pathogens. Pediococcus pentosaceus strain 4012 (LAB 4012) isolated from the cobia intestine was found to be able to increase the respiratory burst activity and resistance against photobacteriosis in cobia (Xing, 2010). The aim of this study is to examine the probiotic potential of LAB 4012 in groupers. After 4-week feeding with LAB 4012 and then GIV challenge, the accumulated mortality of LAB 4012-fed groupers was 40% lower than that of the non-fed fish. In addition, C3 and Mx gene expression level are raised in head-kidney and intestine after 4-week feeding. Groupers fed with LAB 4012 for one and three weeks, the respiratory burst and phagocytic activity were significantly elicited, and LAB 4012 could be reisolated from the intestine of the fed fish, indicating that LAB 4012 was tolerant to gastric acid and bile salt of grouper and finally resided in the fish intestine and increase grouper innate immunity. In vitro, the pretreatment of GF-3 cells with LAB 4012 culture supernatant did not induce Mx gene expression in GF-3 cells, but inhibited about 37% of GIV to enter the host cells, indicating that some components in the LAB 4012 metabolites might block the GIV receptor on the GF-3 cells. Moreover, LAB 4012 culture supernatant could down-regulate NNV RNA synthesis. According to the above data, we suggested that LAB 4012 has probiotic potential to improve the resistance against viral diseases in groupers.