초기 유생단계 참굴, Crassostrea gigas에 대한 Vibrio의 병원성
Virulence of Vibriosis in Larva Stage of Pacific oyster, Crassostrea gigas
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Vibrio splendidus biovar II와 V. anguillarum이 우리나라 굴 유생에 있어서 bacillary necrosis를 일으킬 가능성이 있는지를 알아보기 위하여 인 위감염을 실시하였다. 부화 후 5일생 유생은 V. splendidus biovar II를 1.81×10⁴ CFU/㎖ 농도로 인위감염 시켰을 때 8시간 후부터 폐사가 시작 되어 16시간에 100% 폐사를 보였다. V. anguillarum을 1.13×10⁵ CFU/㎖의 농도로 인위감염 시킨 실험구에서는 20시간 후부터 폐사가 시작 되어 24시간 후 5.55-20%의 폐사율을 보였다. 부화 후 10일생 유생은 V. splendidus biovar II 5.0×10⁵ CFU/㎖ 실험구에서 공격 후 8시간째부터 폐사가 나타나기 시작하여 24시간 후 90.47% 폐사하였으나, V. anguillarum 실험구는 5.08× 103-6 CFU/㎖의 농도범위에서 폐사가 나타나지 않았다. 그러므로 V. splendidus biovar II는 5일생 유생에 강한 병원성이 있음을 확인하였다. 항균 제 처리효과를 구명함으로써 조기 대처방안을 확립하기 위하여 Vibrio를 인위감염 시킨 굴 유 생에 폐사가 나타나기 시작할 때 oxytetracycline 과 streptomycin을 30 ㎍/㎖의 농도로 처리하였 다. 그 결과 굴 유생의 유의적인 생존율 증가는 볼 수 없었으나 생존시간이 다소 길어졌으므로 항균제 처리 시점 및 사용농도에 대한 추가연구 의 필요성이 제기되었다. 인위감염 실험 시 수 조내의 세균농도 분석 결과, V. anguillarum은 1.13×10⁵ CFU/㎖에서 4시간 때 일시적인 증가 를 보이다 시간이 경과할수록 1.7×10⁵ CFU/㎖ 로 차츰 감소하는 경향을 보였고, V. splendidus biovar II는 1.81×10⁴CFU/㎖에서 1.7×10⁷ CFU/ ㎖로 증가하여 강한 생존력을 보였다. 이와 같 은 생존력의 차이는 두 균주간의 병원성 차이를 보이는 결과와 일치하였다. 국내에서는 보고된 바 없지만 세계적으로 패류인공종묘에 대량폐 사의 원인이 되는 V. splendidus biovar II의 국내 산 굴 유생에 대한 병원성이 확인되어 국내에서 도 bacillary necrosis의 발생 가능성이 높음을 알 수 있었다.
Abstract
The potential pathogenicity of Vibrio splendidus biovar II, which was isolated from triploid larvae of pacific oyster with bacillary necrosis and fish pathogenic V. anguillarum were investigated. The 5-day-old larvae infected with V. splendidus biovar II at the dose of 1.81×10⁴ CFU/㎖ started to die within 8 hours after exposure and the mortality were reached to 100% in 16 hours. However, 1.13×104-5 CFU/㎖ of V. anguillarum caused 5.5-20% mortality of the larvae after 24 hours. The 10-day-old larvae infected with V. splendidus biovar II at the dose of 5.0×10⁵ CFU/㎖ showed mortality from 8 hours after challenge and led to a marked mortality of 90.47% after 24 hours. But V. anguillarum at doses of 5.08×103-6 CFU/㎖ did not show mortality in the 10-day-old larvae. Therefore V. splendidus biovar II exhibited stronger virulence in 5-day-old larvae than 10-day-old and young oyster. Changes in the concentration of Vibrio in sea water showed that V. anguillarum decreased from 1.13×10⁵ CFU/㎖ to 1.7×10⁵ CFU/㎖ and V. splendidus biovar II increased from 1.81×10⁴ CFU/㎖ to 1.7×10⁷ CFU/㎖. This strong survival ability of V. splendidus biovar II in seawater was thought as one of the virulence factors against oyster larvae. The mortalities of 5-day-old and 10-day-old oyster larvae were decreased by addition of 30 ㎍/㎖ of antibacterial agent(oxytetracycline or streptomycin). These results suggest that bacillary necrosis by V. splendidus biovar II can be occurred in oyster larvae in Korea. And virulence of V. splendidus biovar II is stronger than that of V. anguillarum in oyster larvae causing significant mortality at the density of 10⁴ CFU/㎖.
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