Colonization factor of thermostable direct hemolysinproducing Vibrio parahaemolyticus in the alimentary tract of a gastropod, Clithon retropictus

利用扫描电镜（SEM）研究了产耐热直接溶血素（TDH）的副溶血弧菌在河口腹足类Clithon retropictus消化道中的定殖及该腹足类对消化道内微生物的防御反应。在冲绳和三重县的河口调查了4种腹足类（Clithonfaba，C.corona，Neritinaplumbea和Septariapportia）的生态和腹足类中产生TDH的菌株，发现它们分布在冲绳岛北方的河口微咸水区。在前4种腹足类分布区附近的淡水区，都有反纹隐翅虫的出现，而在咸水区则很少见到。由于副溶血性弧菌不能在淡水中存活，因此副溶血性弧菌被认为与前四种腹足类动物有关，而不是冲绳河口的反褶曲栉孔扇贝。1996年8月，在三重县的Miya河和五十铃河河口的反褶曲栉孔扇贝中检测到产TDH菌株，其水平分别为2.1*10^5/g和3.0/g，但在四种腹足类动物中未检测到产TDH菌株。将副溶血弧菌D3菌株经口接种于日本冲绳的反纹梭菌（C.retropictus），并将其培养在盐度为20 ~* 的紫外线照射的循环人工海水中。在适当的时间间隔内，将腹足动物的消化道取出，用2.5%戊二醛固定，用乙醇脱水，涂铂，在扫描电镜下观察，在粘膜上未观察到微生物。由于已知通过殖民地计数法从消化道中检出的微生物水平个体差异很大，因此可能需要进一步观察。

Colonization of thermostable direct hemolysin (TDH)-producing Vibrio parahaemolyticus in the alimentary tract of an estuarine neritid gastropod, Clithon retropictus, and defense reaction of the gastropod to the organism in the alimentary tract was investigated under scanning electron microscope (SEM). Ecology of neritid gastropods and of the TDH-producing strains in the gastropods were surveyed at estuaries in Okinawa and Mie Prefectures.Four neritid gastropods, Clithon faba, C.corona, Neritina plumbea and Septaria porcellana, ranged at the brackish water areas of estuaries of the northern part of Okinawa island. C.retropictus was seen at the freshwater areas adjacent to the sites where the former four neritid gastropods ranged, though few individuals of the gastropod were seen at the brackishwater area. As V.parahaemolyticus cannot survive in freshwater, V.parahaemolyticus was supposed to be associated with the former four gastropods rather than C.retropictus at estuaries in Okinawa.TDH-producing strain was detected from C.retropictus at estuaries of Miya and Isuzu rivers in Mie Prefecture at a level of 2.1*10^5/g and 3.0/g, respectively, in August, 1996, but not from the four neritid gastropods, C.faba, C.corona, N.plumbea and S.porcellana, in Okinawa by Polymerase Chain Reaction using tdh gene.C.retropictus was inoculated per os by V.parahaemolyticus strain D3 and maintained in UV-irradiated recirculating artificial seawater with a salinity of 20*. At appropriate time intervals, the alimentary tract of the gastropod were removed, fixed with 2.5% glutaraldehyde, dehydrated with ethanol, coated with platinum and observed under SEM.The organism was not seen on the mucous membrane. As the level of the organism detected from the alimentary tract by the colony count method is known to be highly variable individually, further observations might be necessary.