Studies on the lethal effect of ultraviolet light on Trichomonas vaginalis

Following cultivation in Asami medium, centrifugation and resuspension in saline or in water from a medicinal spring, Trichomonas vaginalis trophozoites were exposed to well-defined doses of ultraviolet (UV) light (254 nm). We used 24- and 48-h-old trichomonads at concentrations of 1×10⁵ and 5×10⁴ trophozoites/ml in a total volume of 20 ml for these studies. The apparatus for UV irradiation was especially constructed for batch experiments. After irradiation at doses ranging from 80 to 160 mJ/cm², the mobility of the parasites was reduced and morphological alterations appeared: rounding of the cells, vacuolization of the cytoplasm and even cytolysis. A dose of 401.7 mJ/cm² killed 99.8% of the 48-h-old trichomonads when irradiation occurred in saline at a cell density of 1×10⁵ trichomonads/ml and 98.9% when irradiation was done at a cell density of 5×10⁴ trichomonads/ml. A dose of 362.1 mJ/cm² killed only the more sensitive 24-h-old trichomonads. In mineral water, 241 mJ/cm² was sufficient to kill up to 99.5% of the 48-h-old trichomonads. When 48-h-old trichomonads that had been exposed to a radiation dose of 160-240 mJ/cm² were subcultured, they lost their ability to propagate. At a dose of 80 mJ/cm², both the trichomonads that had been harvested during the log phase and the 48-h-old organisms suspended in mineral water lost their ability to propagate on subculture. These results indicate that 24-h-old trichomonads were more sensitive than 48-h-old organisms. Furthermore, the experiments demonstrated that a higher dose of UV radiation must be applied to T. vaginalis trophozoites than to the more sensitive bacterial strain Escherichia coli ATCC 11229 so as to achieve comparable killing results.