Propagation and in vitro studies of Perkinsus marinus

The development of continuous cultures of Perkinsus marinus (Apicomplexa) is a major breakthrough that will lead to a better understanding of this deadly oyster pathogen. More than 10 P. marinus isolates are currently in continuous cultures. Culture media used to propagate P. marinus range from media designed for the culture of mammalian cells to protein-free chemically defined media. Continuous cultures of P. marinus can be initiated from a variety of infected oyster tissues or from isolated hypnospores (i.e., the enlarged stage of P. marinus from oyster tissue incubated in Ray\u27s fluid thioglycollate medium). P. marinus cells adapt well to culture conditions and optimal temperature, osmolality, pH and seeding density for its propagation are reported. The availability of several P. marinus isolates in cultures has prompted investigations that address the parasite\u27s genetic makeup, virulence and environmental tolerance. These studies, once completed, will provide valuable insights into disease pathogenesis and host-parasite interactions. Several important findings have already been made in the short time since the original culture. For example, it was found that P. marinus secretes serine proteases that digest oyster tissues and plasma. Acid phosphatases and heat shock ( stress ) proteins are also produced by P. marinus. Moreover, it was found that P. marinus extracellular products suppress some oyster host defenses. Studies on the mechanisms of adaptation of P. marinus to environmental conditions as well as on parasite biochemistry and nutritional requirements have also begun. Finally, cultured cells are being used in screening chemotherapeutic agents for their potential use in treating infected oysters. This review is a collation of the available literature on the methods used to propagate P. marinus in vitro and on current investigations conducted with cultured cells. Although it is important to realize some of the limitations of in vitro studies, research using cultured P. marinus cells is indispensable and may lead to novel ways of controlling the parasite