The Survival of Toxoplasma gondii in Various Suspending Media

In the handling of Toxoplasma gondii outside its host organisms, for such purposes as the preparation of standard inocula for test animals, some assurance is necessary that the toxoplasmas remain viable and infective in the media used. If the medium is not adequate, no eal standardization of inocula is possible, especially when the time which elapses following removal of the parasite from the host is extended. Because of these considerations, it has been our practice (Jacobs and Jones, 1950) to limit the time of handling to one hour. However, it is possible that even within such a short period deleterious effects on the toxoplasmas might result from an inadequate medium. Consequently it was considered necessary to assess various fluids for their ability to sustain toxoplasmas without harm and to ascertain reasonably safe time limits for the handling of the parasites in vitro. Some data have been reported in regard to the length of time that Toxoplasmainfected tissue may be stored without loss of the parasite. Sabin and Olitzky (1937) stated that the parasites could be preserved by storing an infected mouse brain in Tyrode's solution in the refrigerator without loss of infectivity for 14 days. Wolf, Cowen, and Paige (1940) kept pieces of brain and spinal cord of a fatal neonatal case of toxoplasmosis in sterile physiological saline for 11 hours at 7 degrees C. without noting any essential difference from fresh material in subsequent inoculations into mice. Manwell and his collaborators (1945) stated that infected tissues kept in the refrigerator seldom showed living toxoplasmas after 48 hours. More recently, however, Manwell and Drobeck (1951) report survival of toxoplasmas in infected mouse brains for as long as 18 days when the tissues were suspended in Difco skim milk and kept in the refrigerator; they noted no differences in the time of development of infections in mice inoculated with stored material. To our knowledge, beyond statements on the susceptibility of toxoplasmas to freezing and drying, there has been no report on the survival of small numbers of the organisms in various fluids which might be used for handling Toxoplasma in the laboratory. In this paper will be presented data on the effects of tissue storage on the toxoplasmas and information on the survival of small numbers of the parasites in saline, broth, and other fluids.