[Preliminary study on preservation and preparation of Giardia standard body by ~(60)Co irradiation].

OBJECTIVE: Preliminary study on preparation methods of Giardia standard body by~(60)Co devitalized and the preservation conditions. METHODS: Giardia irradiated by different doses of~(60)Co 0-1200 Gy and assessed by immunofluorescence assay. In the same time, the inactivated Giardia were preserved in 2. 5% K2Cr2O7 at 4℃. Then the Giardia by immunofluorescence assay was observed over the next 5 months. RESULTS: After treatment with 900 Gy of~(60)Co radiation, 91. 44% ± 1. 64% of the cysts were inactivated. Moreover, indicators of cysts meet the requirements. After stored at 4 ℃ for 4 months, the number of total cysts, inactivation ratio and the morphology of cysts were meet the requirement. CONCLUSION: It is an effective method to inactivate Giardia cysts with 900 Gy irradiation of~(60)Co. And Giardia cysts can be preserved in 2. 5% K2Cr2O7 at 4 ℃ for 4months.

Reactivation of Giardia lamblia cysts after exposure to low-pressure UV irradiation.

In this study, we determined the repair capabilities of Giardia lamblia cysts when they were exposed to low-pressure (LP) UV and then 4 different repair conditions. A UV collimated beam apparatus was used to expose shallow suspensions of G. lamblia cysts in buffered reagent water (PBS, pH 7.2) to various doses of LP UV irradiation. After UV irradiation, samples were exposed to 4 repair conditions (light and dark repair conditions with 2 temperatures (25 °C and 37 °C) for each condition). The inactivation of G. lamblia cysts by LP UV was very extensive (∼ 5 log10) even with a low dose of LP UV (1 mJ/cm(2)). More importantly, there was significant restoration of infectivity in G. lamblia cysts when they were exposed to a low dose of LP UV and then to all the repair conditions tested. Overall, the results of this study indicate that G. lamblia cysts do have the ability to repair their UV-damaged DNA when they are exposed to low doses of LP UV irradiation. This is the first study to report the presence of repair in UV-irradiated G. lamblia cysts.

UV irradiation responses in Giardia intestinalis.

The response to ultraviolet light (UV) radiation, a natural stressor to the intestinal protozoan parasite Giardia intestinalis, was studied to deepen the understanding of how the surrounding environment affects the parasite during transmission. UV radiation at 10 mJ/cm(2) kills Giardia cysts effectively whereas trophozoites and encysting parasites can recover from UV treatment at 100 mJ/cm(2) and 50 mJ/cm(2) respectively. Staining for phosphorylated histone H2A showed that UV treatment induces double-stranded DNA breaks and flow cytometry analyses revealed that UV treatment of trophozoites induces DNA replication arrest. Active DNA replication coupled to DNA repair could be an explanation to why UV light does not kill trophozoites and encysting cells as efficiently as the non-replicating cysts. We also examined UV-induced gene expression responses in both trophozoites and cysts using RNA sequencing (RNA seq). UV radiation induces small overall changes in gene expression in Giardia but cysts show a stronger response than trophozoites. Heat shock proteins, kinesins and Nek kinases are up-regulated, whereas alpha-giardins and histones are down-regulated in UV treated trophozoites. Expression of variable surface proteins (VSPs) is changed in both trophozoites and cysts. Our data show that Giardia cysts have limited ability to repair UV-induced damage and this may have implications for drinking- and waste-water treatment when setting criteria for the use of UV disinfection to ensure safe water.

Development of a combined in vitro cell culture--quantitative PCR assay for evaluating the disinfection performance of pulsed light for treating the waterborne enteroparasite Giardia lamblia.

Giardia lamblia is a flagellated protozoan parasite that is recognised as a frequent cause of water-borne disease in humans and animals. We report for the first time on the use of a combined in vitro HCT-8 cell culture-quantitative PCR assay for evaluating the efficacy of using pulsed UV light for treating G. lamblia parasites. Findings showed that current methods that are limited to using vital stains before and after cyst excystation are not appropriate for monitoring or evaluating cyst destruction post PUV-treatments. Use of the human ileocecal HCT-8 cell line was superior to that of the human colon Caco-2 cell line for in vitro culture and determining PUV sensitivity of treated cysts. G. lamblia cysts were also shown to be more resistant to PUV irradiation compared to treating similar numbers of Cryptosporidium parvum oocysts. These observations also show that the use of this HCT-8 cell culture assay may replace use of animal models for determining disinfection performances of PUV for treating both C. parvum and G. lamblia.

Reactivation of Giardia lamblia cysts after exposure to polychromatic UV light.

AIMS: In this study, we determined the ability of a promising alternative UV technology--a polychromatic emission from a medium-pressure UV (MP UV) technology--to inhibit the reactivation of UV-irradiated Giardia lamblia cysts. METHODS AND RESULTS: A UV-collimated beam apparatus was used to expose shallow suspensions of purified G. lamblia cysts in PBS (pH 7.2) or filtered drinking water to a low dose (1 mJ cm(-2)) of MP UV irradiation. After UV irradiation, samples were exposed to two repair conditions (light or dark) and two temperature conditions (25 °C or 37 °C for 2-4 h). The inactivation of G. lamblia cysts by MP UV was very extensive, and c. 3 log(10) inactivation was achieved with a dose of 1 mJ cm(-2) . Meanwhile, there was no apparent reactivation (neither in vivo nor in vitro) of UV-irradiated G. lamblia under the conditions tested. CONCLUSION: The results of this study indicated that, unlike the traditional low-pressure (LP) UV technology, an alternative UV technology (MP UV) could inhibit the reactivation of UV-irradiated G. lamblia cysts even when the cysts were exposed to low UV doses. SIGNIFICANCE AND IMPACT OF THE STUDY: It appears that alternative UV technology has some advantages over the traditional LP UV technology in drinking water disinfection because of their high level of inactivation against G. lamblia cysts and also effective inhibition of reactivation in UV-irradiated G. lamblia cysts.

Inactivation of Giardia lamblia cysts by cobalt-60 irradiation.

Cysts of Giardia lamblia can be a contaminant of water and food that can infect humans and cause the zoonotic disease giardiasis. Irradiation by a cobalt-60 source was investigated for its ability to inactivate cysts such that they would not be infective to gerbils. Cysts that received doses of radiation ranging from 0.25 to 2.0 kGy, with a recovery period of 6 hr or less, did not infect gerbils. Cysts that were irradiated at 0.25 kGy and allowed to recover at 23 C in water for 24 hr or longer were infective. Temperature had an effect on the ability of cysts to regain infectivity in that cysts allowed to recover at 4 C after irradiation were not infective. Therefore, recovery time and temperature are important parameters for determination of the doses that are necessary for inactivation of this pathogen. The ability of staining with propidium iodide to predict infectivity of cysts was tested. Cysts that were damaged by higher doses of radiation and were not infective to gerbils stained similarly to viable cysts that were infective. Thus, propidium iodide is not a reliable indicator of viability and infectivity of cysts that have been treated with gamma radiation.

Infectivity of Giardia lamblia cysts obtained from wastewater treated with ultraviolet light.

Several waterborne outbreaks of giardiasis have been linked to discharge of wastewater effluents into surface water. Little is known about the infectivity of Giardia lamblia cysts present in UV treated wastewater effluents. In this study, the infectivity of G. lamblia cysts, recovered from primary effluent and secondary effluent, both upstream and downstream of operating full-scale UV reactors at four wastewater treatment plants, was assessed using the Mongolian gerbil model. Infectivity of cysts obtained from the primary effluents was scored as either strong or moderate for induction of infection in gerbils at three out of four wastewater treatment plants. G. lamblia recovered from secondary effluent both upstream and downstream of the UV reactors caused weak infections in the gerbils. The probability of weak infections caused by inoculums of 50-1400 cysts per gerbil was, on the average, reduced by approximately 10% at the four wastewater UV installations with coliform reduction equivalent doses ranging from 6 to 18 mJ/cm2. The UV systems provided considerably less inactivation of the parasite than expected based on the UV dose response of Giardia reported in the literature.

Impact of solar radiation in disinfecting drinking water contaminated with Giardia duodenalis and Entamoeba histolytica/dispar at a point-of-use water treatment.

AIMS: To determine the impact of natural sunlight in disinfecting water contaminated with cysts of Giardia duodenalis and Entamoeba histolytica/dispar using plastic containers. METHODS AND RESULTS: Known quantities of Giardia duodenalis and Entamoeba histolytica/dispar cysts in sterile water were exposed to the sun. Containers were made of polyethylene terephthalate, eight painted black on one side, one not painted and another cut open at the top and the last was a high density polypropylene container. Viability testing was performed using vital and fluorescent dyes. The same assays were conducted under cloudy conditions. Thermal control tests were also performed using heat without ultra violet light from the sun. Results show that 99.9% of parasites was inactivated when water temperatures reached 56 degrees C after sunlight exposure. CONCLUSION: Both solar radiation and heat produced by the sun have a synergistic effect in killing cysts of Giardia duodenalis and Entamoeba histolytica/dispar when temperatures rise above 50 degrees C, with complete death at 56 degrees C, using painted 2-l PET containers. SIGNIFICANCE AND IMPACT OF THE STUDY: Solar disinfection system using PET containers painted black on one side can be used to disinfect water against Giardia duodenalis and Entamoeba histolytica/dispar using natural sunlight.

Luminescent europium nanoparticles with a wide excitation range from UV to visible light for biolabeling and time-gated luminescence bioimaging.

Silica-encapsulated highly luminescent europium nanoparticles with a wide excitation range from UV to visible light (200-450 nm) have been prepared and used for streptavidin labeling and time-gated luminescence imaging of an environmental pathogen, Giardia lamblia.

Photocatalytic disinfection of Giardia intestinalis and Acanthamoeba castellani cysts in water.

In this study, disinfection of water containing Giardia intestinalis and Acanthamoeba castellani cysts with TiO2 and modified catalyst silver loaded TiO2 (Ag-TiO2) was investigated. Destruction of the parasites was evaluated after UV illumination of the suspension consisting 5 x 10(8)-13.5 x 10(8)cysts/mL in the presence of 2g/L neat or modified TiO2 at neutral pH. In the initial stage, the solid photocatalyst particles penetrated the cyst wall and then oxidant species produced by TiO2/UV destroyed both cell wall and intracellular structure. In the case of G. intestinalis inactivation (disinfection) performance of TiO2/UV system reached 52.5% only after 25 min illumination and total parasite disinfection was achieved after 30 min illumination. However, silver loaded TiO2 seemed to be more effective as this loading provided better catalytic action as well as additional antimicrobial properties. Cell viability tests showed that parasite cysts, their walls in particular, were irreversibly damaged and cysts did not re-grow. Nevertheless the studied system seemed to be ineffective for the inactivation of A. castellani. Inactivation percentages of TiO2/UV and Ag-TiO2/UV systems were far lower than that of UV alone, being 50.1% and 46.1%, respectively.

Survival of Giardia lamblia trophozoites after exposure to UV light.

The ability of Giardia lamblia trophozoites to reproduce after exposure to different fluences of UV radiation was determined using an in vitro-cultured method. The rate of parasite reproduction following UV exposure was measured by direct enumeration of trophozoites cultured in Diamond's Trypticase Yeast extract-Iron (TYI)-S-33 medium. The results suggested that some G. lamblia trophozoites may survive or are reactivated following exposure to UV fluences up to 10 mJ cm(-2). In addition, trophozoites exposed to a UV fluence of 1 mJ cm(-2) were infectious to Mongolian gerbils. Evidence of survival or reactivation at UV fluences of 20 and 40 mJ cm(-2) was ambiguous and statistically inconclusive, while at 100 mJ cm(-2) there was no evidence of survival or reactivation. This finding may have implications for criteria used by the drinking water and wastewater treatment industry to ensure safe reduction of G. lamblia cysts by UV disinfection processes.

Comparison of levels of inactivation of two isolates of Giardia lamblia cysts by UV light.

The effects of 254-nm UV irradiation on two human isolates (WB and H3) of Giardia lamblia cysts were assessed using a collimated beam protocol and a Mongolian gerbil model. The levels of infection of cysts in the gerbils were assessed based on the presence of cysts in feces and the presence and activity of trophozoites in the small intestine of inoculated gerbils. The results suggest that there were differences in the infectivities of the WB and H3 isolates, as well as in susceptibilities of the parasites to UV light. Without UV exposure, gerbils were more readily infected by isolate H3 cysts. After UV exposure of the cysts, however, the gerbils were more susceptible to isolate WB cysts.