Simple and rapid measurement of Cryptosporidium excystation using flow cytometry

Microbiological quality of irrigation water for cultivation of fruits and vegetables: An overview of available guidelines, water testing strategies and some factors that influence compliance

Contaminated irrigation water is among many potential vehicles of human pathogens to food plants, constituting significant public health risks especially for the fresh produce category. This review discusses some available guidelines or regulations for microbiological safety of irrigation water, and provides a summary of some common methods used for characterizing microbial contamination. The goal of such exploration is to understand some of the considerations that influence formulation of water testing guidelines, describe priority microbial parameters particularly with respect to food safety risks, and attempt to determine what methods are most suitable for their screening. Furthermore, the review discusses factors that influence the potential for microbiologically polluted irrigation water to pose substantial risks of pathogenic contamination to produce items. Some of these factors include type of water source exploited, irrigation methods, other agro ecosystem features/practices, as well as pathogen traits such as die-off rates. Additionally, the review examines factors such as food safety knowledge, other farmer attitudes or inclinations, level of social exposure and financial circumstances that influence adherence to water testing guidelines and other safe water application practices. A thorough understanding of relevant risk metrics for the application and management of irrigation water is necessary for the development of water testing criteria. To determine sampling and analytical approach for water testing, factors such as agricultural practices (which differ among farms and regionally), as well as environmental factors that modulate how water quality may affect the microbiological safety of produce should be considered. Research and technological advancements that can improve testing approach and the determination of target levels for hazard characterization or description for the many different pollution contexts as well as farmer adherence to testing requirements, are desirable.

Detection and quantification of soil-transmitted helminths in environmental samples: A review of current state-of-the-art and future perspectives

It is estimated that over a billion people are infected with soil-transmitted helminths (STHs) globally with majority occurring in tropical and subtropical regions of the world. The roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and hookworms (Ancylostoma duodenale and Necator americanus) are the main species infecting people. These infections are mostly gained through exposure to faecally contaminated water, soil or contaminated food and with an increase in the risk of infections due to wastewater and sludge reuse in agriculture. Different methods have been developed for the detection and quantification of STHs eggs in environmental samples. However, there is a lack of a universally accepted technique which creates a challenge for comparative assessments of helminths egg concentrations both in different samples matrices as well as between locations. This review presents a comparison of reported methodologies for the detection of STHs eggs, an assessment of the relative performance of available detection methods and a discussion of new emerging techniques that could be applied for detection and quantification. It is based on a literature search using PubMed and Science Direct considering all geographical locations. Original research articles were selected based on their methodology and results sections. Methods reported in these articles were grouped into conventional, molecular and emerging techniques, the main steps in each method were then compared and discussed. The inclusion of a dissociation step aimed at detaching helminth eggs from particulate matter was found to improve the recovery of eggs. Additionally the selection and application of flotation solutions that take into account the relative densities of the eggs of different species of STHs also results in higher egg recovery. Generally the use of conventional methods was shown to be laborious and time consuming and prone to human error. The alternate use of nucleic acid-based techniques has improved the sensitivity of detection and made species specific identification possible. However, these nucleic acid based methods are expensive and less suitable in regions with limited resources and skill. The loop mediated isothermal amplification method shows promise for application in these settings due to its simplicity and use of basic equipment. In addition, the development of imaging soft-ware for the detection and quantification of STHs shows promise to further reduce human error associated with the analysis of environmental samples. It may be concluded that there is a need to comparatively assess the performance of different methods to determine their applicability in different settings as well as for use with different sample matrices (wastewater, sludge, compost, soil, vegetables etc.).

Extracellular excystation and development of Cryptosporidium: tracing the fate of oocysts within Pseudomonas aquatic biofilm systems

Background

Aquatic biofilms often serve as environmental reservoirs for microorganisms and provide them with a nutrient-rich growth environment under harsh conditions. With regard to Cryptosporidium, biofilms can serve as environmental reservoirs for oocysts, but may also support the growth of additional Cryptosporidium stages.

Results

Here we used confocal laser scanning microscopy, scanning electron microscopy (SEM), and flow cytometry to identify and describe various Cryptosporidium developmental stages present within aquatic biofilm systems, and to directly compare these to stages produced in cell culture. We also show that Cryptosporidium has the ability to form a parasitophorous vacuole independently, in a host-free biofilm environment, potentially allowing them to complete an extracellular life cycle. Correlative data from confocal and SEM imaging of the same cells confirmed that the observed developmental stages (including trophozoites, meronts, and merozoites) were Cryptosporidium. These microscopy observations were further supported by flow cytometric analyses, where excysted oocyst populations were detected in 1, 3 and 6 day-old Cryptosporidium-exposed biofilms, but not in biofilm-free controls.

Conclusions

These observations not only highlight the risk that aquatic biofilms pose in regards to Cryptosporidium outbreaks from water distribution systems, but further indicate that even simple biofilms are able to stimulate oocyst excystation and support the extracellular multiplication and development of Cryptosporidium within aquatic environments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-014-0281-8) contains supplementary material, which is available to authorized users.

Multiplication of the waterborne pathogen Cryptosporidium parvum in an aquatic biofilm system

BACKGROUND

In natural aquatic environments biofilms are known to act as environmental reservoirs for Cryptosporidium parvum oocysts. However, the fate of these oocysts within biofilms has yet to be determined.

METHODS

This study aimed to identify if biofilms have the ability to support the multiplication of Cryptosporidium by measuring the change in parasite number over time using quantitative polymerase chain reaction (qPCR) and detecting the possible extracellular developmental stages using a combination of confocal microscopy and immunolabelling techniques. Pseudomonas aeruginosa biofilm flow cell systems were established and C. parvum oocysts were constantly supplied over a six day period.

RESULTS

A significant (P<0.001) increase in Cryptosporidium was detected as the biofilm matured, with the total number of C. parvum multiplying 2-3 fold during this period. With this, various Cryptosporidium developmental stages (sporozoites, trophozoites, type I and II meronts) were identified from the biofilm.

CONCLUSION

This is the first study demonstrating that biofilms not only serve as an environmental reservoir for oocysts, but are also capable of supporting the multiplication of Cryptosporidium over time in an aquatic environment.

Rapid detection and enumeration of Giardia lamblia cysts in water samples by immunomagnetic separation and flow cytometric analysis

Giardia lamblia is an important waterborne pathogen and is among the most common intestinal parasites of humans worldwide. Its fecal-oral transmission leads to the presence of cysts of this pathogen in the environment, and so far, quantitative rapid screening methods are not available for various matrices, such as surface waters, wastewater, or food. Thus, it is necessary to establish methods that enable reliable rapid detection of a single cyst in 10 to 100 liters of drinking water. Conventional detection relies on cyst concentration, isolation, and confirmation by immunofluorescence microscopy (IFM), resulting in low recoveries and high detection limits. Many different immunomagnetic separation (IMS) procedures have been developed for separation and cyst purification, so far with variable but high losses of cysts. A method was developed that requires less than 100 min and consists of filtration, resuspension, IMS, and flow cytometric (FCM) detection. MACS MicroBeads were used for IMS, and a reliable flow cytometric detection approach was established employing 3 different parameters for discrimination from background signals, i.e., green and red fluorescence (resulting from the distinct pattern emitted by the fluorescein dye) and sideward scatter for size discrimination. With spiked samples, recoveries exceeding 90% were obtained, and false-positive results were never encountered for negative samples. Additionally, the method was applicable to naturally occurring cysts in wastewater and has the potential to be automated.

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.

Flow cytometric assessment of distinct physiological stages withinCryptosporidium parvumsporozoites post-excystation

Cryptosporidium parvumare protozoan parasites responsible for outbreaks of gastrointestinal disease worldwide. Within the apical complex of this organism reside numerous vesicular secretory organelles and their discharge has been identified as essential for sporozoite motility, cell attachment and penetration. Traditionally, investigation of apical organelle discharge has relied on microscopic and immunochemical hybridization techniques. In this study we demonstrate for the first time how flow cytometry, in combination with vital dye staining, provides an avenue for discrimination of distinct physiological events occurring withinCryptosporidiumsporozoites post-excystation. Time-course studies of freshly excysted sporozoites were carried out at 37°C in cell-free medium, stained with the fluorescent dyes SYTO9/PI, DiBAC4(3), Fluo-4 AM or FM1-43 and analysed by flow cytometry. Significant decreases in sporozoite plasma membrane permeability and increased membrane depolarization were found to be accompanied by concomitant increases in intracellular calcium. Subsequent to these changes, large increases in exocytosed vesicular membrane were apparent. In addition, by measuring side and forward angle light scatter we were able to assess changes in internal granularity and size of sporozoites post-excystation. These observations were suggestive of rapid mobilization, utilization and discharge of apical organelles within sporozoites, which we relate to changes in sporozoite infectivity, ATP levels and total secreted soluble protein.

Flow cytometry and environmental microbiology

This survey unit discusses many of the issues involved for flow cytometry in the field of microbiology, particularly the preparative procedures, which are far more stringent than many other procedures using larger cells. For instance, it is often necessary to filter laboratory agents multiple times to obtain the true particle-free solutions needed for flow cytometry of microbes. It is difficult enough to recognize bacteria in cell extracts from soil, sediment, or sludge given the background of same-size particles. This unit provides an excellent overview of a potentially large application area in flow cytometry and is written by one of the most respected scientists in the field.

Solar UV reduces Cryptosporidium parvum oocyst infectivity in environmental waters

AIMS

To determine the effect of solar radiation on Cryptosporidium parvum in tap and environmental waters.

METHODS AND RESULTS

Outdoor tank experiments and a cell culture infectivity assay were used to measure solar inactivation of C. parvum oocysts in different waters. Experiments conducted on days with different levels of solar insolation identified rapid inactivation of oocysts in tap water (up to 90% inactivation within the first hour). Increased dissolved organic carbon content in environmental waters decreased solar inactivation. The role of solar ultraviolet (UV) in inactivation was confirmed by long-pass filter experiments, where UV-B was identified as the most germicidal wavelength. Reductions in oocyst infectivity following solar radiation were not related to a loss of excystation capacity.

CONCLUSIONS

Solar UV can rapidly inactivate C. parvum in environmental waters.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to assess natural sunlight inactivation of C. parvum oocysts in surface waters and drinking water using an infectivity measure and determines the wavelengths of light responsible for the inactivation. The findings presented here provide valuable information for determining the relative risks associated with Cryptosporidium oocysts in aquatic environments and identify solar radiation as a critical process affecting the oocyst survival in the environment.

Viability staining and animal infectivity of Cryptosporidium andersoni oocysts after long-term storage

Preservation of biological properties of oocysts during the storage is critical for experimental work. Stomach species of cryptosporidia are less resistant against external influences, and their infectivity decreases rapidly in comparison with intestinal cryptosporidia. Cryptosporidium andersoni oocysts lost their infectivity for gerbil (Meriones unguiculatus) after 7 months storage in deionised water (DW) or in 2.5% potassium dichromate solution (PDS). Evaluation of oocyst viability by flow cytometry indicates higher percentage of viable oocysts stored in PDS than in DW, particularly after 6 months of storage. However, direct counting using fluorescent microscope revealed that these results are false and are influenced by the change of staining properties during the storage in PDS. Moreover, the examination of oocyst integrity by flow cytometry revealed that oocysts preserved in PDS kept their wall integrity longer than those stored in DW, and this fact should be taken into consideration during quantification of oocyst survival.

Environmental inactivation of Cryptosporidium oocysts in catchment soils

AIMS

To generate field-relevant inactivation rates for Cryptosporidium oocysts in soil that may serve as parameter values in models to predict the terrestrial fate and transport of oocysts in catchments.

METHODS AND RESULTS

The inactivation of Cryptosporidium oocysts in closed soil microcosms over time was monitored using fluorescence in situ hybridization (FISH) as an estimate of oocyst 'viability'. Inactivation rates for Cryptosporidium in two soils were determined under a range of temperature, moisture and biotic status regimes. Temperature and soil type emerged as significantly influential factors (P < 0.05) for Cryptosporidium inactivation. In particular, temperatures as high as 35 degrees C may result in enhanced inactivation.

CONCLUSIONS

When modelling the fate of Cryptosporidium oocysts in catchment soils, the use of inactivation rates that are appropriate for the specific catchment climate and soil types is essential. FISH was considered cost-effective and appropriate for determining oocyst inactivation rates in soil.

SIGNIFICANCE AND IMPACT OF THE STUDY

Previous models for predicting the fate of pathogens in catchments have either made nonvalidated assumptions regarding inactivation of Cryptosporidium in the terrestrial environment or have not considered it at all. Field-relevant inactivation data are presented, with significant implications for the management of catchments in warm temperate and tropical environments.

Evaluation of Cryptosporidium parvum oocyst recovery efficiencies from various filtration cartridges by electrochemiluminescence assays

AIMS

To evaluate four types of filtration cartridges for their capacities, efficiency for capture and release of Cryptosporidium parvum oocysts for detection.

METHODS AND RESULTS

Filtration cartridges included in this evaluation were IDEXX Filta-Max, Gelman Envirochek HV, Corning CrypTest, and Filterite Sigma+. Various dosages of C. parvum oocysts were spiked into water samples with a wide range of turbidity (10-50 NTU). Electrochemiluminescence assays were employed to enumerate viable or total number of C. parvum oocysts in these eluates. Among the cartridges tested, Filta-Max consistently showed higher oocyst recovery efficiency, especially with large volume, highly turbid water samples.

CONCLUSIONS

Filta-Max filter is the best performer because of its higher oocyst recovery efficiency.

SIGNIFICANCE AND IMPACT OF THE STUDY

The overall sensitivities of various C. parvum oocyst detection assays in water samples can be improved if highly efficient oocyst recovery filtration cartridges such as Filta-Max are incorporated in sample preparation.

Fluorescence resonance energy transfer (FRET)-based specific labeling ofCryptosporidium oocysts for detection in environmental samples

BACKGROUND

Accurate detection and quantification of Cryptosporidium oocysts in water are a challenge to the water industry. This article demonstrates a way to fluorescently label Cryptosporidium oocysts, based on fluorescence resonance energy transfer (FRET). Labeled oocysts can then be applied to environmental waters and their movement followed by flow cytometric detection and enumeration of the FRET-labeled oocysts, as demonstrated here with environmental water samples.

METHODS

Cryptosporidium oocysts were labeled with three fluorochromes, FITC, Texas red, and Cy7, that through FRET yielded a Stokes shift of approximately 272 nm with excitation from a standard argon laser emitting at 488 nm. Defined flow cytometric settings and gatings were used to select FITC/green (530-nm), Texas red/red (650-nm), and Cy7/infrared (780-nm) fluorescing particles with light scatter properties similar to oocysts. Water concentrates were seeded with 10 tri-labeled oocysts and were analyzed using flow cytometry. Unseeded water concentrates were also analyzed.

RESULTS

Analysis of unseeded water concentrates detected no autofluorescent particle similar to the labeled oocysts. Labeled oocysts were detected successfully with up to 85% recovery in water concentrates spiked with 10 tri-labeled oocysts.

CONCLUSIONS

Low numbers of FRET-labeled oocysts can be quantified and clearly distinguished from autofluorescing background in environmental water concentrates.

Evaluation of a combined immunomagnetic separation/flow cytometry technique for epidemiological investigations of Cryptosporidium in domestic and Australian native animals

A combined immunomagnetic separation (IMS) and flow cytometry (FC) technique was developed for the sensitive detection of Cryptosporidium in faecal samples. The IMS/FC technique was found to be approximately 50-fold more sensitive than formol-ether concentration, which is commonly used for Cryptosporidium epidemiological investigations. Of 31 faecal samples from captive animals 16 were found to contain Cryptosporidium oocysts when analysed using the IMS/FC compared to four when using formol-ether concentration (FEC). In a wild population of eastern grey kangaroos Macropus giganteus 66.3% of infected animals were shedding <500oocysts/gfaeces when analysed using IMS/FC. This is below the detection limit for the FEC method. The dispersal of Cryptosporidium in host populations is aggregated, with many individuals shedding low numbers of oocysts and few individuals shedding numbers of oocysts sufficiently high to be detected by FEC. This research demonstrates that the prevalence and oocyst shedding intensity of Cryptosporidium in animal populations will be significantly underestimated using standard detection methods.

Emerging waterborne infections: contributing factors, agents, and detection tools

Because microorganisms are easily dispersed, display physiological diversity, and tolerate extreme conditions, they are ubiquitous and may contaminate and grow in water. The presence of waterborne enteric pathogens (bacteria, viruses, and protozoa) in domestic water supplies represents a potentially significant human health risk. Even though major outbreaks of waterborne disease are comparatively rare, there is substantial evidence that human enteric pathogens that are frequently present in domestic water supplies are responsible for low-level incidence of waterborne microbial disease. Although these diseases are rarely debilitating to healthy adults for more than a few hours to a few days, enteric pathogens can cause severe illness, even death, for young children, the elderly, or those with compromised immune systems. As the epidemiology of waterborne diseases is changing, there is a growing global public health concern about new and reemerging infectious diseases that are occurring through a complex interaction of social, economic, evolutionary, and ecological factors. New microbial pathogens have emerged, and some have spread worldwide. Alternative testing strategies for waterborne diseases should significantly improve the ability to detect and control the causative pathogenic agents. In this article, we provide an overview of the current state of knowledge of waterborne microbial pathogens, their detection, and the future of new methods in controlling these infectious agents.

Cryptosporidium parvum and Cyclospora cayetanensis: a review of laboratory methods for detection of these waterborne parasites

Cryptosporidium and Cyclospora are obligate, intracellular, coccidian protozoan parasites that infest the gastrointestinal tract of humans and animals causing severe diarrhea illness. In this paper, we present an overview of the conventional and more novel techniques that are currently available to detect Cryptosporidium and Cyclospora in water. Conventional techniques and new immunological and genetic/molecular methods make it possible to assess the occurrence, prevalence, virulence (to a lesser extent), viability, levels, and sources of waterborne protozoa. Concentration, purification, and detection are the three key steps in all methods that have been approved for routine monitoring of waterborne oocysts. These steps have been optimized to such an extent that low levels of naturally occurring Cryptosporidium oocysts can be efficiently recovered from water. The filtration systems developed in the US and Europe trap oocysts more effectively and are part of the standard methodologies for environmental monitoring of Cryptosporidium oocysts in source and treated water. Purification techniques such as immunomagnetic separation and flow cytometry with fluorescent activated cell sorting impart high capture efficiency and selective separation of oocysts from sample debris. Monoclonal antibodies with higher avidity and specificity to oocysts in water concentrates have significantly improved the detection and enumeration steps. To date, PCR-based detection methods allow us to differentiate the human pathogenic Cryptosporidium parasites from those that do not infect humans, and to track the source of oocyst contamination in the environment. Cell culture techniques are now used to examine oocyst viability. While fewer studies have focused on Cyclospora cayetanensis, the parasite has been successfully detected in drinking water and wastewater using current methods to recover Cryptosporidium oocysts. More research is needed for monitoring of Cyclospora in the environment. Meanwhile, molecular methods (e.g. molecular markers such as intervening transcribed spacer regions), which can identify different genotypes of C. cayetanensis, show good promise for detection of this emerging coccidian parasite in water.

Estimating viability of Cryptosporidium parvum oocysts using reverse transcriptase-polymerase chain reaction (RT-PCR) directed at mRNA encoding amyloglucosidase

The purpose of the present study was to determine if reverse transcriptase-polymerase chain reaction (RT-PCR) directed at mRNA encoding the enzyme amyloglucosidase (CPAG) could serve as a indicator for C. parvum oocyst viability. Oocysts were stored for 1-11 months in the refrigerator and at monthly intervals extracted for total RNA for RT-PCR analysis. An aliquot of these C. parvum oocysts was inoculated into neonatal mice which were necropsied 4 days later for ileal tissue that was analyzed by semi-quantitative PCR to determine the level of parasite replication. The CPAG RT-PCR assay detected RNA from as few as 10(3) C. parvum oocysts. An effect of storage time on both RT-PCR signal and mouse infectivity was observed. RNA from oocysts stored for 1-7 months, unlike oocysts stored for 9 or 11 months, contained CPAG mRNA that was detectable by RT-PCR. A gradual decrease in the RT-PCR signal intensity was observed between 5 and 7 months storage. The intensity of RT-PCR product from oocysts and the signal from semi-quantitative PCR of ileal tissue DNA from mice infected with these same aged oocysts were comparable. The RT-PCR assay of CPAG mRNA in cultured cells infected with viable C. parvum oocysts first detected expression at 12 h with highest expression levels observed at 48 h post-infection. These results indicate that CPAG RT-PCR may be useful for differentiating viable from non-viable C. parvum oocysts and for studying the expression of the gene for amyloglucosidase in vitro.

Quantitative flow cytometric evaluation of maximal Cryptosporidium parvum oocyst infectivity in a neonate mouse model

The importance of waterborne transmission of Cryptosporidium parvum to humans has been highlighted by recent outbreaks of cryptosporidiosis. The first step in a survey of contaminated water currently consists of counting C. parvum oocysts. Data suggest that an accurate risk evaluation should include a determination of viability and infectivity of counted oocysts in water. In this study, oocyst infectivity was addressed by using a suckling mouse model. Four-day-old NMRI (Naval Medical Research Institute) mice were inoculated per os with 1 to 1,000 oocysts in saline. Seven days later, the number of oocysts present in the entire small intestine was counted by flow cytometry using a fluorescent, oocyst-specific monoclonal antibody. The number of intestinal oocysts was directly related to the number of inoculated oocysts. For each dose group, infectivity of oocysts, expressed as the percentage of infected animals, was 100% for challenge doses between 25 and 1,000 oocysts and about 70% for doses ranging from 1 to 10 oocysts/animal. Immunofluorescent flow cytometry was useful in enhancing the detection sensitivity in the highly susceptible NMRI suckling mouse model and so was determined to be suitable for the evaluation of maximal infectivity risk.

An immunoglobulin G1 monoclonal antibody highly specific to the wall of Cryptosporidium oocysts

The detection of Cryptosporidium oocysts in drinking water is critically dependent on the quality of immunofluorescent reagents. Experiments were performed to develop a method for producing highly specific antibodies to Cryptosporidium oocysts that can be used for water testing. BALB/c mice were immunized with six different antigen preparations and monitored for immunoglobulin G (IgG) and IgM responses to the surface of Cryptosporidium oocysts. One group of mice received purified oocyst walls, a second group received a soluble protein preparation extracted from the outside of the oocyst wall, and the third group received whole inactivated oocysts. Three additional groups were immunized with sequentially prepared oocyst extracts to provide for a comparison of the immune response. Mice injected with the soluble protein extract demonstrated an IgG response to oocysts surface that was not seen in the whole-oocyst group. Mice injected with whole oocysts showed an IgM response only, while mice injected with purified oocyst walls showed little increase in IgM or IgG levels. Of the additional reported preparations only one, BME (2-mercaptoethanol treated), produced a weak IgM response to the oocyst wall. A mouse from the soluble oocyst extract group yielding a high IgG response was utilized to produce a highly specific IgG(1) monoclonal antibody (Cry104) specific to the oocyst surface. Comparative flow cytometric analysis indicated that Cry104 has a higher avidity and specificity to oocysts in water concentrates than other commercially available antibodies.

Survival ofCryptosporidium parvumoocysts in source separated human urine

The survival of Cryptosporidium parvum in source separated urine was investigated as part of a broader study on microbial risks associated with the reuse of human urine for sustainable agriculture. A dye permeability assay and in vitro excystation were the primary methods used to assess viability. In the collected urine most of the nitrogen is present as ammonia and the pH is generally around 9. Parallel investigations were made in buffers to compare possible toxic effects of urine to actual pH effects. Oocysts in the untreated urine were inactivated below the detection limit (1/300) within 63 days. This inactivation rate was significantly higher (P < 0.01) than in urine adjusted to pH 5 or 7 according to the dye permeability assay. The corresponding difference between different pH values was not seen in buffers, suggesting that the antiprotozoan effect of urine was mediated by other factors besides pH. The Swedish practice of storing urine for six months before its use thus appears satisfactory for the inactivation of Cryptosporidium oocysts.Key words: Cryptosporidium parvum, oocysts, human urine, survival, source separation.

Rapid method for fluorescent in situ ribosomal RNA labelling of Cryptosporidium parvum

A method for fluorescence in situ hybridization (FISH) is described that requires less than 1 h duration. Oocysts were resuspended in 50% ethanol and incubated at 80 degrees C for 10 min for simultaneous fixation and permeabilization. Samples were than incubated with the oligonucleotide probe at 48 degrees C for more than 30 min. The rRNA binding specificity of the optimized protocol was confirmed. FISH was found to be valuable as a second label for oocysts presumptively identified immunofluorescently, but required more than an order of magnitude signal amplification for independent use. The number of oligonucleotide probes bound per oocyst was compared with the copy number of 18S rRNA molecules per oocyst to provide a measure of the labelling efficiency of the FISH method. Hybridization kinetics were also analysed. These data indicate that significant further increases in the brightness of FISH-labelled oocysts cannot be achieved by further optimization of the pre-treatment and hybridization conditions.

Viable Cryptosporidium parvum oocysts exposed to chlorine or other oxidising conditions may lack identifying epitopes

The intestinal protozoan parasite Cryptosporidium parvum is a known cause of water-borne disease in humans. The detection of Cryptosporidium oocysts in water samples relies upon the use of fluorescently labelled antibodies, preferably using flow cytometry and epifluorescence microscopy. Here we demonstrate that four commercially available antibodies recognise a similar set of immunodominant epitopes on the oocyst wall. These epitopes appear to be carbohydrate in nature and are labile to chlorine treatment and oxidising conditions. Sodium hypochlorite and sodium meta-periodate reduced the ability of the antibodies to detect Cryptosporidium oocysts. Damage to the epitopes did not necessarily reduce the viability of oocysts. This finding may be important for the water industry, where naturally occurring oxidising conditions or sanitizing treatments could produce viable oocysts that are undetectable using standard protocols.