Blastocystis hominis undergoing programmed cell death via cytotoxic gamma irradiation

Blastocystis hominis is a worldwide common enteric parasite. Its pathogenic potential has not yet been established, although many reports suggest that it may cause the development of various gastrointestinal symptoms. The aim of the present study is to evaluate the destructive effect of different doses of cytotoxic gamma (γ) irradiation combined with and compared to metronidazole (MTZ) on Blastocystis spp. in vitro. The detection of the parasite in the stool specimen was conventionally done by light microscopic examination of direct smears, cultivation, followed by PCR-sequencing. Evaluation of γ-irradiation and MTZ effects on B. hominis was carried out by trypan blue exclusion assay, caspase activity detection, acridine orange staining, DNA fragmentation assay and transmission electron microscopic (TEM) examination. The current study demonstrated that exposure to γ-irradiation in a dose of 0.5 kGray (kGy) significantly (P < 0.05) reduced the viability of B. hominis subtype 2 by 95.2% compared to the untreated and MTZ-treated parasites (87.1%) after 48 h incubation. Combining the same dose of irradiation (0.5 kGy) with MTZ yielded a viability reduction of 94.2% and 94% after 24 and 48 h respectively, which were statistically significant (P < 0.05) compared to MTZ alone. Moreover, our results showed features of programmed cell death in the form of morphological, biochemical, and molecular changes (TEM abnormalities, caspase-like activity, and DNA fragmentation, respectively) with the high doses of γ-irradiation (0.3 and 0.5 kGy) either singly or combined with MTZ. In conclusion, cytotoxic γ-irradiation plays an important role in the inactivation of Blastocystis spp., so, it can be a promising prophylactic water-sterilizing tool against blastocystosis.