Detection of infectious Cryptosporidium oocysts by cell culture immunofluorescence assay: applicability to environmental samples

Molecular Identification of Parasitic Protozoa Sarcocystis in Water Samples

Simple Summary

Members of the genus Sarcocystis are protozoan parasites having two-host prey–predator cycle. These parasites are widespread in farm animals. Sarcocystis species are characterized morphologically in intermediate hosts, and these parasites are identified in definitive hosts by molecular methods. Thus far, only few studies have been conducted on Sarcocystis parasites in environmental samples. The aim of the present work was to evaluate several sample preparation and polymerase chain reaction methods for the identification of several Sarcocystis species in water samples. Overall, 114 samples collected from various water sources, ponds, canals, lakes, lagoons, and rivers in Lithuania were tested for the presence of Sarcocystis spp. Based on molecular methods, eight Sarcocystis species, S. bovifelis, S. cruzi, S. hirsuta, S. arieticanis, S. tenella, S. capracanis, S. bertrami, and S. miescheriana, were identified. The main intermediate hosts of detected Sarcocystis parasites are cattle, sheep, goats, horses, and pigs. Further, more sensitive molecular techniques are needed for the development of the diagnosis of Sarcocystis species in water bodies.

Abstract

Sarcocystis parasites are among the most common parasitic protozoa in farm animals. So far, the diversity of these parasites has been mainly studied in animal carcasses by morphological or molecular methods. Research on parasitic protozoa in environmental samples is scarce due to the lack of an appropriate methodology and low concentrations of parasites. For these reasons, there is a paucity of validated methods for Sarcocystis identification from environmental samples. Therefore, the present study aims to investigate various molecular methods for Sarcocystis parasite identification in water samples. In the present study, the sample volume, sporocysts isolation, and various conventional PCR were evaluated, and species-specific primers for the identification of different Sarcocystis species have been developed. Of the methods studied, based on data the most appropriate method for the identification of analyzed Sarcocystis spp. in water bodies is nested PCR, using species-specific primers targeting the cox1 gene. Sarcocystis DNA was detected in 111 out of 114 (97.4%) samples. This paper represents the first identification of S. bovifelis, S. cruzi, S. hirsuta, S. arieticanis, S. tenella, S. capracanis, S. bertrami, and S. miescheriana by PCR and sequencing in environmental water samples. Our pilot study is useful in developing techniques for the identification of Sarcocystis species from water samples.

Calcium-Mediated Biophysical Binding of Cryptosporidium parvum Oocysts to Surfaces Is Sensitive to Oocyst Age

Cryptosporidium parvum causes potentially life-threatening gastrointestinal disease in humans and may not be effectively removed from drinking water via conventional methods. Prior research has shown that environmental biofilms immobilize oocysts from the water column, but the biophysical mechanisms driving this attraction are still under investigation. This study investigates the affinity of C. parvum oocysts to silanized surfaces. Surfaces were prepared with hydroxyl, amine, and carboxyl moieties. Binding forces between the oocysts and these engineered substrates were analyzed, with and without divalent ions, using atomic force microscopy. Binding forces were measured over several weeks to investigate the influence of age on adhesion. C. parvum oocysts bind most strongly to carboxylic acid functional groups, with rupture forces greater than that required to break noncovalent molecular bonds, regardless of oocyst age. This adhesion is shown to be due to divalent cation bridging mechanisms. In addition, the binding strength increases over a 5-week period as the oocysts age, followed by a decrease in the binding strength, which may be related to structural or biochemical changes in the outer wall-bound glycosylated proteins. This study sheds new light on the biochemical parameters that influence C. parvum oocyst binding to surfaces. Increased understanding of how age and water chemistry influence the binding strength of oocysts may inform future developments in environmental detection and drinking water treatment, such as with the development of oocyst-specific sensors that allow for more frequent tracking of oocysts in the environment.IMPORTANCE The mechanisms by which pathogens bind to surfaces are of interest to a wide variety of scientific communities, as these mechanisms drive infectivity, fate, and transport of the pathogenic organisms. This study begins to reveal the mechanism of direct binding of Cryptosporidium parvum to surfaces containing both carboxylic acid and amine moieties, in an attempt to understand how much of the binding ability is due to long-range electrostatic forces versus other mechanisms (specific or nonspecific) of bonding. In addition to improving the scientific understanding of fate and transport of oocysts, an expanded understanding of the binding mechanisms may aid in the development of new tools and sensors designed to detect and track oocysts in waterways. Furthermore, the methods used to examine binding in this study could be translated to other waterborne pathogens of interest.

Cryptosporidium and Giardia in Wastewater and Surface Water Environments

and spp. are significant contributors to the global waterborne disease burden. Waterways used as sources of drinking water and for recreational activity can become contaminated through the introduction of fecal materials derived from humans and animals. Multiple studies have reported the occurence or concentrations of these pathogens in the environment. However, this information has not been comprehensively reviewed. Quantitative microbial risk assessment (QMRA) for and can be beneficial, but it often relies on the concentrations in environmental sources reported from the literature. A thorough literature review was conducted to develop an inventory of reported and concentrations in wastewater and surface water available in the literature. This information can be used to develop QMRA inputs. and (oo)cyst concentrations in untreated wastewater were up to 60,000 oocysts L and 100,000 cysts L, respectively. The maximum reported concentrations for and in surface water were 8400 oocysts L and 1000 cysts L, respectively. A summary of the factors for interpretation of concentration information including common quantification methods, survival and persistence, biofilm interactions, genotyping, and treatment removal is provided in this review. This information can help in identifying assumptions implicit in various QMRA parameters, thus providing the context and rationale to guide model formulation and application. Additionally, it can provide valuable information for water quality practitioners striving to meet the recreational water quality or treatment criteria. The goal is for the information provided in the current review to aid in developing source water protection and monitoring strategies that will minimize public health risks.

The Biological Basis for Ballast Water Performance Standards: "Viable/Non-Viable" or "Live/Dead"?

The shipping industry is critical to international commerce; however, contemporary shipping practices involve uptake and discharge of ballast water, which introduces the potential for transfer of nonindigenous, invasive species among geographically distinct habitats. To counteract this hazard, regulations for ballast water management have been implemented by the International Maritime Organization (IMO) and by regulatory agencies such as the United States Coast Guard (USCG). IMO and USCG discharge standards are numerically identical, but involve different definitions of treatment end points, which are based on fundamentally different biological assays for quantification of ballast water treatment effectiveness. Available assays for quantification of the responses of organisms in the 10-50 μm size range include vital stains based on fluorescein diacetate (FDA), sometimes used in combination with 5-chloromethylfluorescein diacetate (CMFDA), observations of motility, and the most probable number dilution culture method (MPN). The mechanisms and implications of these assays are discussed relative to the Type Approval process, which quantitatively evaluates compliance with ballast water discharge standards (BWDSs) under controlled shipboard and land-based tests. For antimicrobial processes that accomplish treatment by preventing subsequent replication of the target species, the FDA/CMFDA and MPN methods can yield dramatically different results. An important example of a treatment process that is affected by the choice of assay is ultraviolet (UV) irradiation. Results of laboratory and field experiments have demonstrated UV-based technologies to be effective for accomplishing the objectives of ballast water treatment (inactivation of cellular reproduction), when the MPN assay is used as the basis for evaluation. The FDA, CMFDA, motility, and MPN methods are subject to well recognized sources of error; however, the MPN method is based on a response that is consistent with the objectives of ballast water management as well as the mechanism of action of UV-based inactivation. Complementary assays are available for use in compliance testing; however, the development of relevant indicative tests remains as a research priority. Historical lessons learned from applications of vital stains (and other indirect methods) for quantification of microbial responses to UV irradiation in other settings also support the use of assays that provide a direct measure of growth and reproduction, such as MPN. Collectively, these observations point to the use of MPN assays as the standard for type testing, especially when UV-based treatment is employed.

Assessing viability and infectivity of foodborne and waterborne stages (cysts/oocysts) of Giardia duodenalis, Cryptosporidium spp., and Toxoplasma gondii: a review of methods

Giardia duodenalis, Cryptosporidium spp. and Toxoplasma gondii are protozoan parasites that have been highlighted as emerging foodborne pathogens by the Food and Agriculture Organization of the United Nations and the World Health Organization. According to the European Food Safety Authority, 4786 foodborne and waterborne outbreaks were reported in Europe in 2016, of which 0.4% were attributed to parasites including Cryptosporidium, Giardia and Trichinella. Until 2016, no standardized methods were available to detect Giardia, Cryptosporidium and Toxoplasma (oo)cysts in food. Therefore, no regulation exists regarding these biohazards. Nevertheless, considering their low infective dose, ingestion of foodstuffs contaminated by low quantities of these three parasites can lead to human infection. To evaluate the risk of protozoan parasites in food, efforts must be made towards exposure assessment to estimate the contamination along the food chain, from raw products to consumers. This requires determining: (i) the occurrence of infective protozoan (oo)cysts in foods, and (ii) the efficacy of control measures to eliminate this contamination. In order to conduct such assessments, methods for identification of viable (i.e. live) and infective parasites are required. This review describes the methods currently available to evaluate infectivity and viability of G. duodenalis cysts, Cryptosporidium spp. and T. gondii oocysts, and their potential for application in exposure assessment to determine the presence of the infective protozoa and/or to characterize the efficacy of control measures. Advantages and limits of each method are highlighted and an analytical strategy is proposed to assess exposure to these protozoa.

A new in vitro model using small intestinal epithelial cells to enhance infection of Cryptosporidium parvum

To better understand and study the infection of the protozoan parasite Cryptosporidium parvum, a more sensitive in vitro assay is required. In vivo, this parasite infects the epithelial cells of the microvilli layer in the small intestine. While cell infection models using colon, kidney, and stomach cells have been studied to understand the infectivity potential of the oocysts, an ideal in vitro model would be readily-available, human-derived, and originating from the small intestine. In this study, we developed a reproducible, quantitative infection model using a non-carcinoma, human small intestinal epithelial cell type, named FHs 74 Int. Our results show that FHs 74 Int cells are productively infected by viable oocysts, and exhibit higher levels of infection susceptibility compared to other cell types. Moreover, infection rate of the sporozoites on the monolayer was found to be comparable or better than other cell types. We furthermore demonstrate that infection can be improved by 65% when pre-treated oocysts are directly inoculated on cells, compared to inoculation of excysted sporozoites on cells. Identification of a better infection model, which captures the preferred site of infection in humans, will facilitate studies on the host pathogenesis mechanisms of this important parasitic human pathogen.

Assessment of the viability of Cryptosporidium parvum oocysts with the induction ratio of hsp70 mRNA production in manure

Determining the presence of viable Cryptosporidium parvum oocysts in complex environmental matrices in hygiene control can prevent the contamination of water resources and food with this pathogen. This study assessed the induction ratio of hsp70 mRNA production by heat shock in different oocysts as a marker of viability. Using different procedures for (m)RNA extraction directly from manure and reverse transcription real-time qPCR, this study found slightly increased hsp70 mRNA contents in viable oocysts that were heat shock induced at 45°C for 20 min compared to not induced oocysts (1.6 fold induction in average). Prolonging the heat shock treatment to 2h did not further increase the copy numbers. Heat shock by consecutive stimuli, such as freezing and then heating, did not yield significantly higher copy numbers than the 45°C treatment. There was a certain background level of hsp70 mRNA in viable oocysts that were not exposed to heat shock, indicating a constitutive production of the transcripts in the oocysts. The production of hsp70 mRNA induced by heat shock in oocysts aged for 9 months that exhibited reduced viability was lower than in fresher oocysts (induction ratio<1.2). No production of hsp70 mRNA by heat shock was detected in 12 months old oocysts that were not viable in the excystation test. Oocysts inactivated at 75°C for 30 min were not able to respond to heat shock, and low amount of copies were occasionally measured only in total RNA extracts, but not in mRNA extracts that were purified directly with an oligo (dT)25 based system. The induction ratio of hsp70 mRNA varied according to the viability of the organisms in a sample. Copy numbers of β-tubulin mRNA in viable oocysts were lower than hsp70 mRNA, therefore the latter is more suitable to detect low numbers of oocysts by RT-qPCR.

In vitro evaluation of the suppressive effect of chitosan/poly(vinyl alcohol) microspheres on attachment of C. parvum to enterocytic cells

We present a new strategy to suppress the attachment of Cryptosporidium parvum to the enterocytes cell surface by bioadhesive microspheres. An optimized microsphere system based on chitosan/poly(vinyl alcohol) was prepared by experimental design for the delivery of Diloxanide Furoate-cyclodextrin complex. Formulations were characterized in terms of size, surface charge, drug release, IR spectroscopy and morphology. Bioadhesion properties of chitosan/poly(vinyl alcohol) microspheres, evaluated in the human enterocytic HCT-8 model, were concentration and time dependent. In vitro efficacy of chitosan/poly(vinyl alcohol) microspheres against Cryptosporidium was tested in infected cultures and stages of parasite were assessed by immunofluorescence. The degree of adherence to cells and the inhibition of infectivity were directly related with the lowest level of cross-linking. The C. parvum attachment to cells surface was efficiently suppressed by a concentration of 100 μg/ml of microspheres. TEM observations showed no epithelial-cell damage when microspheres were co-incubated in infected cultures. These results were coincident with the lack of toxicity in cytocompatibility studies. Microspheres remained adhered after 72 h to the apical area of enterocytes. The results suggest that chitosan/poly(vinyl alcohol) with adequate size and appropriate surface characteristics suppress by impairment the attachment of sporozoites to enterocytes and may have a great potential in the oral chemotherapy of Cryptosporidium infections.

In vitro determination of anticryptosporidial activity of phytogenic extracts and compounds

Cryptosporidiosis caused by Cryptosporidium spp. is an important diarrhoeal disease observed in farm animals and humans, especially in young or immunocompromised individuals. A novel cell culture assay for testing extracts and pure compounds against Cryptosporidium parvum in 96-well microplate format was established and evaluated. It is based on previously described indirect fluorescent antibody techniques and was optimised for higher sample throughput. Rapid assessment of minimal inhibitory concentrations (MICs) was done by checking each well microscopically for the presence or absence of parasite stages. As a novelty, parasite development was quantified by enumeration of clusters of secondary infection (CSI), which typically appeared upon infection with a distinct parasite inoculum after a defined incubation time. Host cell (HCT-8) viability was measured by an integrated non-destructive water-soluble tetrazolium salt assay (WST-1), which facilitated discrimination of antiparasitic activity from possible cytotoxic effects of a test compound against the host cells. Host cell viability was regarded unimpaired when cultures had 75% or more viability when compared to control cultures without test substance. In this study, a maximum density of distinguishable CSI was obtained when cultures were infected with 2.5 × 10(3) oocysts and incubated for 48 h. The applicable inoculum has to be optimised for each batch of oocysts and before each experimental series. Parasite development was inhibited completely by monensin at 134 nM and silymarin at 50 mg/mL. These concentrations were non-toxic to the host cells and comparable to literature data. The percentages of parasite inhibition were determined for monensin and a 50% inhibitory concentration (IC(50)) of 36.6 nM (27.4-45.5) and a 90% inhibitory concentration of 65.9 nM (54.8-90.2) were calculated. The introduced assay is economic because relatively low parasite numbers may be used. If MICs are determined, evaluation is fast, as each well is viewed only briefly under the fluorescence microscope for presence or absence of CSI. Furthermore it is highly critical because only full parasite inhibition is assessed. Counting of CSI is more laborious and time-consuming, but it allows calculation of parasite inhibition rates and parameters like the half maximal inhibitory concentration (IC(50)). This assay shall be used to assess anticryptosporidial activities of various plant waste materials and by-products from the food and the pharmaceutical industries in the course of the EU project SAFEWASTES. Comparison with in vivo models should be performed to further corroborate the results. Automated evaluation by flow cytometry might facilitate higher sample throughput and reduce operator bias.

Leaching of Cryptosporidium parvum oocysts, Escherichia coli, and a Salmonella enterica serovar Typhimurium bacteriophage through intact soil cores following surface application and injection of slurry

Increasing amounts of livestock manure are being applied to agricultural soil, but it is unknown to what extent this may be associated with contamination of aquatic recipients and groundwater if microorganisms are transported through the soil under natural weather conditions. The objective of this study was therefore to evaluate how injection and surface application of pig slurry on intact sandy clay loam soil cores influenced the leaching of Salmonella enterica serovar Typhimurium bacteriophage 28B, Escherichia coli, and Cryptosporidium parvum oocysts. All three microbial tracers were detected in the leachate on day 1, and the highest relative concentration was detected on the fourth day (0.1 pore volume). Although the concentration of the phage 28B declined over time, the phage was still found in leachate at day 148. C. parvum oocysts and chloride had an additional rise in the relative concentration at a 0.5 pore volume, corresponding to the exchange of the total pore volume. The leaching of E. coli was delayed compared with that of the added microbial tracers, indicating a stronger attachment to slurry particles, but E. coli could be detected up to 3 months. Significantly enhanced leaching of phage 28B and oocysts by the injection method was seen, whereas leaching of the indigenous E. coli was not affected by the application method. Preferential flow was the primary transport vehicle, and the diameter of the fractures in the intact soil cores facilitated transport of all sizes of microbial tracers under natural weather conditions.

Cryptosporidiumcell culture infectivity assay design

Members of the genusCryptosporidium, which cause the gastrointestinal disease cryptosporidiosis, still represent a significant cause of water-borne disease worldwide. While intensive efforts have been invested in the development of techniques for parasite culture,in vitrogrowth has been hampered by a number of factors including low levels of infectivity as well as delayed life-cycle development and poor synchronicity. In this study we examined factors affecting the timing of contact between excysted sporozoites and target host cells and the subsequent impact of this upon the establishment of infection. We demonstrate that excystation rate impacts upon establishment of infection and that in our standard assay format the majority of sporozoites are not close enough to the cell monolayer when they are released from the oocyst to successfully establish infection. However, this can be easily overcome by centrifugation of oocysts onto the cell monolayer, resulting in approximately 4-fold increases in sporozoite attachment and subsequent infection. We further demonstrate that excystation procedures can be tailored to control excystation rate to match the assay end purpose and that excystation rate can influence data interpretation. Finally, the addition of both a centrifugation and washing step post-sporozoite attachment may be appropriate when considering the design ofin vitroculture experiments for developmental analysis and stage-specific gene expression as this appears to increase the synchronicity of early developmental stages.

Improved risk analysis by dual direct detection of total and infectious Cryptosporidium oocysts on cell culture in combination with immunofluorescence assay

The inactivation of Cryptosporidium oocysts is a main driver in the selection of water treatment disinfection strategies, and microbial risk analysis provides a sound basis for optimizing water treatment processes. U.S. Environmental Protection Agency method 1622/23 provides an estimate of the total oocyst count; however, it cannot be used directly for risk assessment, as it does not determine the fraction of infectious oocysts. Improved assessment of the risk for designated sources or in treated water requires evaluation of the total number of oocysts and an estimate of their infectivity. We developed a dual direct detection method using differential immunofluorescent staining that allows detection of both oocysts and cell culture infection foci for each sample. Using Cryptosporidium parvum oocysts, various pH levels, proteases, and gastroenteric compounds and substrates were assessed to determine their abilities to enhance the number of infection foci. The results showed that the key trigger for oocyst stimulation was acidification. Addition of a low concentration of D-glucose (50 mM) to the infection media increased rates of infectivity, while a higher dose (300 mM) was inhibitory. The total number of oocysts in each sample was determined by counting the oocysts remaining on a cell monolayer and the oocysts recovered from cell monolayer washes during processing using a simple filtration technique. With the dual direct detection on cell culture with immunofluorescence assay method, it is now possible to determine the numbers of total and infectious oocysts for a given sample in a single analysis. Direct percentages of infectivity are then calculated, which allows more accurate assessments of risk.

Evaluation of two methods for quantification of hsp70 mRNA from the waterborne pathogen Cryptosporidium parvum by reverse transcription real-time PCR in environmental samples

We optimized and evaluated two mRNA extraction methods to quantify induced hsp70 mRNA from viable and injured Cryptosporidium parvum oocysts by reverse transcription quantitative real-time PCR (RT-qPCR) in raw and treated manure. Methods based on guanidinium isothiocyanate/phenol/chloroform (GITC-PC) purification and direct mRNA extraction with magnetic oligo(dT)25-coated beads were evaluated for applicability and sensitivity. Both methods proved to be suitable for processing manure samples. With washed manure samples and oocyst disruption by bead beating for 165 s in time intervals with cumulative pooling of the lysate fractions, optimum RT-qPCR results were achieved. On average, 2.6 times more hsp70 mRNA was detected with the oligo(dT)25 method in comparison to the GITC-PC based method using fresh oocysts, whereas less mRNA was detected in aged oocysts. For fresh oocysts, analytical and method detection limits for the oligo(dT)25 based method were 1.7 cDNA copies/qPCR reaction and 5150 oocysts/mL manure, and for the GITC-PC based method 17 cDNA copies/qPCR reaction and 4950 oocysts/mL, respectively. In 12 months old oocysts with reduced viability, mRNA was occasionally detected only by the GITC-PC based method. Failure of or reduced detection with the oligo(dT)25 based method was apparently a result of weakened oocyst walls leading to quicker release of mRNA and therefore mRNA shredding by bead beating in the relatively long stretch between the capture sequence and the RT-qPCR target sites.

Microbial indicators and pathogens: removal, relationships and predictive capabilities in water reclamation facilities

Four water reclamation facilities in north-eastern Spain were monitored over 2 years to determine the occurrence and concentrations of a set of microbial indicators (total coliforms, Escherichia coli, enterococci, spores of sulphite reducing clostridia, somatic coliphages, F-specific RNA phages, phages infecting Bacteroides fragilis strain RYC2056 and phages infecting Bacteroides tethaiotaomicron strain GA-17), and two selected pathogens (cytopathogenic enteroviruses and viable Cryptosporidium oocysts). The indicator (survival) and index (presence) functions of the various indicators tested were evaluated through the wastewater treatments. The inactivation pattern of all groups of bacteriophages tested was closer to the inactivation of enteroviruses than to the inactivation of the conventional bacterial indicators tested. The inactivation of sulfite reducing clostridia spores and bacteriophages more closely approximates the reduction of viable Cryptosporidium than do the conventional bacterial indicators. We observed neither index functions nor a predictive relationship between any of microbial indicators and viable Cryptosporidium oocysts. In contrast, several regression models (r>0.6) and discriminant functions (67-88% well classified samples) based mostly on numbers of bacteriophages were able to predict both the presence and concentrations of enteroviruses. A combination of both bacterial and bacteriophage indicators seem to be the best choice for ensuring the microbial quality of reclaimed water.

Microbial adhesion of Cryptosporidium parvum: identification of a colostrum-derived inhibitory lipid

We previously described an unidentified lipid purified from calf small intestine that inhibits the in vitro adhesion of Cryptosporidium parvum sporozoites to host cells [Johnson JK, Schmidt J, Gelberg HB, Kuhlenschmidt MS. Microbial adhesion of Cryptosporidium parvum sporozoites: purification of an inhibitory lipid from bovine mucosa. J Parasitol 2004;90:980-90]. Intestinal mucosa from some calves, however, failed to yield this bioactive lipid. Accordingly, we examined other potential sources, especially dietary sources, of the inhibitory lipid and discovered it was principally derived from bovine colostrum. Interestingly, fresh colostrum yielded little or no inhibitory lipid, however, the lipid was found in relatively large quantities following incubation of colostrum with the aqueous fraction of calf intestinal contents. Using FAB-MS and NMR analysis, the sporozoite inhibitory lipid (SIL) was identified as oleic acid, a monounsaturated fatty acid likely released from colostrum triglycerides and phospholipids by digestion in the lumen of the calf small intestine. Oleic acid dose-dependently inhibited in vitro sporozoite-host cell adhesion with an inhibitory constant (IC(50)) of approximately 5 microM. Comparison of oleic acid with other C-18 fatty acids revealed linolenic, but not stearic acid, also displayed potent inhibitory activity. Neither linolenic nor oleic acid, however, affect either sporozoite or host cell viability at concentrations that inhibit sporozoite adhesion. These results suggest certain colostrum-derived long-chain fatty acids may serve as natural inhibitors of the early steps in C. parvum sporozoite-host cell interactions.

Comparing the efficacy of chlorine, chlorine dioxide, and ozone in the inactivation of Cryptosporidium parvum in water from Parana State, Southern Brazil

In the present work, assays were performed to compare the efficacy of hypochlorous acid, chlorine dioxide, and ozone in the inactivation of Cryptosporidium oocyst in public water supply from Brazilian South conditions. Experiments were carried out in samples containing 2 x 10(4) oocysts/ml of C. parvum purified from feces of experimentally contaminated calves. An in vitro excystation method was used to evaluate oocysts' viability and to determine the inactivation rates of hypochlorous acid at 2 ppm, chlorine dioxide at 1, 2, and 5 ppm, and ozone at the doses of 0.18, 0.24, 0.36, 0.48, and 1.44 mg/l. By using hypochlorous acid, the maximum inactivation rate obtained was 49.04% after 120 min. Chlorine dioxide at 5 ppm inactivated 90.56% of oocysts after 90 min of contact. Ozone was the most effective product, rendering an inactivation of 100% with the concentration of 24 mg/l. Resistance of Cryptosporidium to the usual disinfectants and the need for more effective water treatments to prevent waterborne diseases in Brazil are discussed in this manuscript.

Aged HCT-8 cell monolayers support Cryptosporidium parvum infection

Cell culture assays in various formats have been used to study the infectivity of Cryptosporidium spp. as well as to determine the infectivity of naturally occurring oocysts in water. Currently, cell culture assays for infectious Cryptosporidium spp. in water have largely been limited to practice in research laboratories. One obstacle to the routine use of Cryptosporidium cell culture assays for the analysis of water samples is the coordination of water sample collection and processing with readiness of cell culture monolayers. For most Cryptosporidium cell culture assays, monolayers are allowed to develop for 24 to 48 h to reach 80 to 100% confluence prior to inoculation. In this study, we used immunofluorescent assay microscopy to evaluate freshly confluent (2-day-old) and aged (8- to 67-day-old) HCT-8 cell monolayers for their ability to support Cryptosporidium parvum infection. HCT-8 monolayers as old as 67 days were clearly shown to support infection. In two of three experiments, aged monolayers (8- to 11-day-old and 11- to 22-day-old, respectively) developed the same number of C. parvum clusters of infection as freshly confluent monolayers. Results suggest that it may be possible to use cell monolayers from freshly confluent to 3 weeks old on hand for infectivity assays without having to schedule sample processing to coincide with development of freshly confluent monolayers. This would make Cryptosporidium cell culture assays much more feasible for water quality and utility laboratories.

Comparison of most probable number-PCR and most probable number-foci detection method for quantifying infectious Cryptosporidium parvum oocysts in environmental samples

Microbial contamination of public water supplies is of significant concern, as numerous outbreaks, including Cryptosporidium, have been reported worldwide. Detection and enumeration of Cryptosporidium parvum oocysts in water supplies is important for the prevention of future cryptosporidiosis outbreaks. In addition to not identifying the oocyst species, the U.S. EPA Method 1622 does not provide information on oocyst viability or infectivity. As such, current detection strategies have been coupled with in vitro culture methods to assess oocyst infectivity. In this study, a most probable number (MPN) method was coupled with PCR (MPN-PCR) to quantify the number of infectious oocysts recovered from seeded raw water concentrates. The frequency of positive MPN-PCR results decreased as the oocyst numbers decreased. Similar results were observed when MPN was coupled to the foci detection method (MPN-FDM), which was done for comparison. For both methods, infectious oocysts were not detected below 10(3) seeded oocysts and the MPN-PCR and MPN-FDM estimates for each seed dose were generally within one-log unit of directly enumerated foci of infection. MPN-PCR estimates were 0.25, 0.54, 0 and 0.66 log(10) units higher than MPN-FDM estimates for the positive control, 10(5), 10(4) and 10(3) seed doses, respectively. The results show the MPN-PCR was the better method for the detection of infectious C. parvum oocysts in environmental water samples.