Cryopreservation of viable Giardia intestinalis trophozoites

A technique is described for the cryopreservation of Giardia intestinalis trophozoites. The most satisfactory results were obtained when organisms were preserved with either 7.5 or 10% dimethyl sulphoxide (Me2SO) and cooled using a liquid nitrogen controlled freezer. Under these conditions more than 70% of organisms were motile after thawing. Lower recovery rates were obtained using glycerol as the cryopreservant or when samples were placed directly into a -70 degrees C refrigerator to cool. Cultures were successfully re-established from material cooled under controlled conditions using either 7.5% Me2SO or glycerol as the cryopreservant. However, the former had an initial generation time of 12.0 hours compared to 24.5 hours for the latter.