Entamoeba histolytica: Inhibition in vitro by bithionol of respiratory activity and growth

Endogenous and 2-propanol-supported respiration of intact trophozoites of Entamoeba histolytica (stain HM-1:IMSS) were inhibited by bithionol, an effective chemotherapeutic agent for some trematode and cestode infections in humans. Dichlorophene and hexachlorophene also inhibited 2-propanol-supported respiration of the parasite. In contrast, ethanol formation by E. histolytica extract in the presence of N₂ was scarcely inhibited by bithionol. The compound also inhibited in vitro growth of axenic (HM-1 strain) and polyxenic (strain HJ-1:KEIO) amoebae in culture. It took less than 24 hr to kill and disrupt virtually all amoebae of either strain with 0.28 mM bithionol. Omission of bovine serum from BI-S-33 medium resulted in considerably less disruption of HM-1 strain amoebae by the compound. However, organisms that looked undisrupted were stained with trypan blue. Moreover, the number of amoebae incubated for 10 min in the serum-free BI-S-33 medium containing 0.14 mM bithionol did not increase, even after incubation for 24 hr following replacement of the experimental culture fluid with fresh complete BI-S-33 medium free of the compound. These findings suggest that, although serum appears to diminish the antiamoebic action, some halogenated bisphenols (in particular bithionol) may be useful for treatment of amoebiasis.