The use of infectivity titrations for measurement of the viability of Entamoeba histolytica after cryopreservation.

An infectivity titration technique is described for the measurement of the viability of Entamoeba histolytica. Using this method an optimal cryopreservation technique has been developed. When amoebae from young cultures were equilibrated with 7.5% dimethylsulphoxide for 15 minutes at 37 degrees C, cooled to -100 degrees C at 1 degree C per minute, and stored in liquid nitrogen, 1 to 2% regularly survived after thawing rapidly at 37 degrees C and, on occasions, 10 to 12% survived.