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

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 07660420
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Applied veterinary science
• Research Institution: University of the Ryukyus
• Principal Investigator: KUMAZAWA Norichika University of the Ryukyus, Tropical Biosphere Research Center, Professor, 熱帯生物圏研究センター, 教授 (00039926)
• Project Period (FY): 1995 – 1996
• Keywords: Vibrio parahaemolyticus / Clithon retropictus / neritid gastropod / alimentary tract / reservoir / TDH

Research Abstract

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.