The action of ameobicidal drugs on Entamoeba invadens Rodhain, 1934 in vitro

Modification and elimination of the bacterial flora in cultures ofEntamoeba invadensRodhain, 1934

1. Cysts, formed in a strain ofE. invadensgrowing with a mixed bacterial flora, were sterilized of all but one species of bacterium (organismx), by treatment with chemicals. Strains ofE. invadensderived from these cysts were prepared, growing with organismxand eitherBact. coliorB. megatherium.

2. A monobacterial strain ofE. invadens, growing withBact. colialone, was obtained by maintaining a dibacterial strain, growing with organismxandBact. coli, for 72 days in medium containing gentian violet.

3. A monobacterial strain ofE. invadens, growing withStaph. albus, was prepared from cysts, produced in the monobacterial strain ofE. invadens + Bact. coli, and sterilized by treatment with chemicals.

4. An axenic strain ofE. invadenswas prepared by maintaining the monobacterial strain ofE. invadens + Staph. albus, in saline-liver medium containing antibiotics. This axenic strain has now been maintained for over 14 months in saline containing untreated, sterile liver, but no antibiotics.

Studies on Entamoeba invadens Rodhain, 1934, in vitro, and its relationship to some other species of Entamoeba

1. Optimum growth of E. invadens occurred in HSre + S in the presence of Bact. coli, at 24–30° C. The amoebae could not be ‘trained’ to grow above 35° C.

2. The amoebae ingested normal rat erythrocytes, but not those of chick or frog.

3. Mass encystation occurred only under conditions which favoured the growth of the amoebae, but was not dependent on an acceleration in growth rate; in certain strains, an increased production of cysts was correlated with the depletion of starch in the medium.

4. The amoebae were always killed by treatment with N/20-HCl for 1 hr. at room temperature, although usually they did not survive after treatment for only 10 min. At room temperature, the cysts survived treatment with N/10-HC1 for at least 6 days, and with 0·002% HgCl2 for at least 4 hr.

5. The amoebae of E. invadens were adversely affected by aerobic conditions.

6. The amoebae could survive for up to 35 days at 8° C. but for not more than 7 days at 37° C. The cysts survived for at least 14 days at 8° C., for 7, but not 11, days at 24° C., and for less than 7 days at 37° C.

7. It is suggested that, in view of the morphological identity of E. aulastomi, E. invadens, E. moshkovskii and E. histolytica, and the fact that the amoebae of these groups form a series growing at increasingly higher temperatures, these four organisms constitute subspecies rather than full species. The taxonomic status of E. ranarum is still open to question.