Selective survival of a thermostable direct hemolysin-producing Vibrio parahaemolyticus in the alimentary tract of a juvenile estuarine gastropod (Clithon retropictus)

Juvenile estuarine gastropods (Clithon retropictus), maintained in ultraviolet ray-irradiated recirculating artificial seawater with a salinity of 20 parts per thousand at 28 degrees C, preserved thermostable direct hemolysin (TDH)-producing strain D-3 of Vibrio parahaemolyticus at a level of 10(4)-10(5) colony forming units per gram (cfu/g) and TDH-non-producing strains N-18 and R-13 at a level of 10(1)-10(2) cfu/g in the alimentary tract for at least 21 days after ingestion. In adults, the numbers of the three strains decreased to a level of 100 cfu/g within 21 days under the same conditions. This evidence supports our recent observations that TDH-producing strains increased to a high level in the summer months in the presence of high levels of TDH-non-producing strains in the alimentary tract of juvenile C. retropictus at estuaries in Japan.