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

利用扫描电子显微镜（SEM）研究了产耐热直接溶血素（TDH）副溶血性弧菌在河口反刍腹足动物（Clithon retropictus）消化道内的定植，以及腹足动物对消化道内病原菌的防御反应。对冲绳县和三重县河口的浅海腹足类和腹足类中产tdh菌株的生态学进行了调查。在冲绳岛北部河口的咸淡水域分布着四种浅海纲腹足类动物，分别是：蚕豆小腹、冠状小腹、水蛭小腹和小腹。在与前4种浅海腹足动物分布地点相邻的淡水区发现了逆转录腹足动物，而在咸淡水区发现的腹足动物很少。由于副溶血性弧菌不能在淡水中生存，故推测其与冲绳河口的前四种腹足类动物有亲缘关系，而与原腹足动物无亲缘关系。1996年8月，在三县宫宫河河口和五十铃河河口分别检测到产tdh菌株，水平分别为2.1*10^5/g和3.0/g，但在冲绳县的4种neritid腹足类动物c.a faba、c.c rocorona、n.p plumbea和s.p porcellana中未检测到产tdh菌株。在适当的时间间隔，取出腹足动物的消化道，用2.5%戊二醛固定，用乙醇脱水，涂上铂，在扫描电镜下观察。粘膜上未见微生物。由于已知通过菌落计数法从消化道中检测到的生物体水平是高度可变的，因此可能需要进一步的观察。

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.