Ecological Cycle of Thermostable Direct Hemolysin-Producing Strains of Vibrio parahaemolyticus in a Brackish-Water Area with Special Reference to Molluscs and Attached Microalgae

Prevalences of thermostable direct hemolysin (TDH)-producing strains in communities of a gastropod mollusc, Clithon retropictus, and a bivalve mollusc, Corbicula japonica, and levels of the strains in attached microalgae and muddy sediments were investigated at a brackish-water area along Hashizu Creek and Togo Pond in Japan. V. parahaemolyticus was detected from attached microalgae at Hashizu Creek in summer months with the highest level of 1.4×105 cfu/g. Levels of the organism among 20 animals of C. retropictus and C. japonica at the area varied betwen non-detectable level and 103 per mollusc in summer months. TDH was detected from culture supernatants of 11-16% of strains isolated from the algae, sediments and C. japonica and 28% of those isolated from C. retropictus at Hashizu Creek. These evidences suggest that C. retropictus would get TDH-positive strains from the algae.