Effects of triclosan on growth, viability and fatty acid synthesis of the oyster protozoan parasite Perkinsus marinus

Perkinsus marinus, a protozoan parasite of the Eastern oyster Crassostrea virginica, has severely impacted oyster populations from the Mid-Atlantic region to the Gulf of Mexico coast of North America for more than 30 yr. Although a chemotherapeutic treatment to reduce or eliminate P. marinus from infected oysters would be useful for research and hatchery operations, an effective and practical drug treatment does not currently exist. In this study, the antimicrobial drug triclosan 5-chloro-2-(2,4 dichlorophenoxy) phenol, a specific inhibitor of Fab1 (enoyl-acyl-carrier-protein reductase), an enzyme in the Type 11 class of fatty acid synthetases, was tested for its effects on viability, proliferation and fatty acid synthesis of in vitro-cultured P. marinus meronts. Treatment of P. marinus meront cell cultures with concentrations of >= 2 mu M triclosan at 28 degrees C (a temperature favorable for parasite proliferation) for up to 6 d stopped proliferation of the parasite. Treatment at >= 5 mu M at 28 degrees C greatly reduced the viability and fatty acid synthesis of meront cells. Oyster hemocytes treated with >= 20 mu M triclosan exhibited no significant (p < 0.05) reduction in viability relative to controls for up to 24 h at 13 degrees C. R marinus meronts exposed to >= 2 mu M triclosan for 24 h at 13 degrees C exhibited significantly (p < 0.05) lower viability relative to controls. Exposure of P. marinus meronts to triclosan concentrations of >= 20 mu M resulted in > 50% mortality of P. marinus cells after 24 h. These results suggest that triclosan may be effective in treating P. marinus-infected oysters.