ECOLOGICAL CYCLE OF THERMOSTABLE DIRECT HEMOLYSIN-PRODUCING STRAINS OF VIBRIO-PARAHAEMOLYTICUS IN A BRACKISH-WATER AREA WITH SPECIAL REFERENCE TO MOLLUSKS 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 x 10(5) cfu/g. Levels of the organism among 20 animals of C. retropictus and C. japonica at the area varied between non-detectable level and 10(3) 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.