Growth and survival, in vitro and in vivo, of Endolimax blattae, an entozoic amoeba of cockroaches.

1) A study of conditions in the natural habitat of hindgut protozoa of Periplaneta americana was carried out with a view to defining conditions for axenic culture of the inquilines. 2) The pH, measured by the glass electrode, of the anterior colon ranged from 7.4 to 8.1 (mean 7.7 + 0.05). 3) Oxidation-reduction potential in the gut ranged from about + 150 mV in the crop to around -170 mV in the colon. 4) The growth and cytology of Endolimax blattae, a small amoeba living in the colon, were studied in vitro for the first time. Growth would occur at 25C. or at 37C. in diphasic medium. 5) The mitotic cycle is similar to that of E. nana of man, but the intranuclear centride persists during interphase. 6) Desiccation of the cysts does not per se render them non-viable providing oxygen is excluded. Cysts probably survive for more than 93 hours under natural conditions. 7) Yields of amoebae and cysts were increased 5-fold in cultures supplied with starch. 8) The optimum pH for growth in vitro of a strain with simplified flora was between 7.5 and 8.0. 9) In the presence of antibiotics, growth of amoebae would take place on non-viable, 56C - inactivated Klebsiella aerogenes plus medium in which they had been grown. Serum was necessary for subcultivation. Autoclaved or boiled bacteria would not support amoebic growth. 10) Oxygen partial pressures above 78 mm Hg suppressed growth in the above medium. Depletion of reducing agents on storage of the medium had the same effect. 11) Experiments on the culture medium indicated the need for factors continuously produced by the non-viable bacterial associate. 12) The relationships of the amoeba with its bacterial associate and with its host are discussed. 13) In appendix one, a species of Polymastix from cockroaches is described. 14) In appendix two, a list of protozoa which have been described from the cockroach hindgut is given.