Survival of entamoeba and related amoebae at low temperature—II. Viability of amoebae and cysts stored in liquid nitrogen

It was found that E. histolytica, E. histolytica-like, E. hartmanni, E. invadens, E. terrapinae, E. moshkovskii grown with a mixed bacterial flora, could be recovered after prolonged storage in liquid nitrogen. The longest period yet tested for E. histolytica is 382 weeks (7·3 years). Storage of amoebae of E. ranarum and E. coli was less successful. E. histolytica amoebae grown axenically or monoxenically were less easily stored than those amoebae grown with a mixed bacterial flora. Cysts were non-viable after freezing. E. histolytica amoebae showed the same virulence to rats and sensitivity to emetine after storage in liquid nitrogen, as was observed before freezing. A summary of a recommended procedure for freezing Entamoeba and related amoebae is given.