Probiotics를 양식넙치에 투여시 Streptococcus iniae에 대한 면역반응 및 병저항성 = Dietary Administration of Probiotics, Bacillus sp. IS-2, Enhance the Innate Immune Response and Disease Resistance of Paralichthys olivaceus against Streptococcus iniae

국문 초록 (Abstract)

본 연구는 양식 넙치 Paralichthys olivaceus 사료 내 생균제 첨가가 넙치의 성장, 면역반응 및 병저항성에 미치는 영향을 평가하였다. 실험사료는 넙치용 배합사료(조단백질 52%, 조지방 11%, 조섬유 3%, 조회분 14%, 인 2.7%, 칼슘 1.5%, Suhyup Co., Korea)에 Bacillus sp. IS-2를 첨가하여 $10^3$, $10^5$, $10^7$ CFU/kg의 실험사료를 제작하였다. 2주간의 예비사육 후, 평균무게 $210{\pm}13g$인 실험어를 1,000 L 원형수조에 실험구 당 70마리씩 무작위로 배치하여 실험사료를 1일 2회 어체 중의 2%씩 12주 동안 공급하였다. 성장도 조사 결과 모든 실험구에서는 일반사료를 투여한 대조구에 비해 높은 성장률을 나타내었으며 $10^5$ CFU/kg 실험구에서는 대조구에 비해 약 13% 정도 높은 성장률을 나타내었다. 혈액분석 결과에는 glucose를 제외한 GOT, GPT, 단백질, 총콜레스테롤 등에서 실험구간 유의적인 차이를 나타내지 않아 생균제로 인한 간독성이나 어체 내 문제가 발생하지 않은 것으로 사료된다. Glucose인 경우 실험 종료 시점에서 증가되는 변화를 확인 할 수 있었는데 이는 수온, 수질에 의한 일시적인 현상이라 사료된다. Respiratory burst activity (NBT assay)에 있어서는 실험사료를 공급한 실험구가 대조구에 비해 높은 값을 확인할 수 있었으며 특히 $10^5$ CFU/kg 실험구와 $10^7$ CFU/kg 실험구에서 유의적으로 높은 값을 확인하였다. 혈청의 lysozyme 및 백혈구 활성에 있어서도 실험사료를 투여한 실험구에서 대조구에 비해 높은 활성을 확인 하였다. 공격실험 결과, Streptococcus inae를 접종한지 5일째부터 폐사가 시작되어 7일째 일반사료를 투여한 대조구에서는 100% 폐사율을 보인 반면, $10^3$ CFU/kg 실험구에서는 73%의 폐사율을 $10^5$ CFU/kg 실험구에서는 53%의 폐사율을 나타냈으며, $10^7$ CFU/kg 실험구에서는 45%의 폐사율을 보여 대조구에 비해 많게는 55% 이상의 높은 생존율을 나타내었다. 사료 내 첨가한 Bacillus sp. IS-2의 장내 생존 확인을 위해 실험이 종료 된 후 모든 실험구와 대조구 실험어의 장을 분리하여 배양 된 균체를 DNA를 분리 한 후에 제작 된 ditection primer를 이용한 PCR 결과 일반사료를 투여한 대조구를 제외한 모든 실험구에서 1,465 bp의 PCR product를 확인 할 수 있었다. 상기 결과를 토대로 양식넙치 사료 내 Bacillus sp. IS-2의 첨가는 양식넙치의 성장 및 면역증강, S. iniae에 대한 병정항성에 좋은 효과를 나타내어 사료첨가제로써의 이용 가능성이 클 것이라 사료된다.

다국어 초록 (Multilingual Abstract)

The strains were added to the feed in the concentration of $10^3$, $10^5$, and $10^7$ CFU/kg and 2% of fishes were given the feed twice a day (8 AM and 5 PM) for 12 weeks. In result of the nonspecific immune response study to examine Respiratory burst activity, Lysozyme activity and Phagocytosis activity every two weeks until the end of the study, all test samples showed greater activities than control samples and improved immune activity with Bacillus sp. IS-2. The mortality test performed by artificial infection using Streptococcus iniae, a pathogenic bacterium, after the completion of this study also showed over 55% greater survival rate in all test samples. In result of performing PCR using the universal primer to verify that the probiotic stays in the intestines of the fishes, all test samples showed PCR product of 1,465 bp. Based on the above findings, it was concluded that Bacillus sp. IS-2 in the feed improved farmed flatfish's immune system and resistance against diseases as the probiotics. Also, the physiological indicators discovered by this study would be useful for identifying the mechanisms of probiotics.

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