Detection of Cryptosporidium oocysts in water: techniques for generating precise recovery data

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.

Comparison of next-generation droplet digital PCR (ddPCR) with quantitative PCR (qPCR) for enumeration of Cryptosporidium oocysts in faecal samples

Clinical microbiology laboratories rely on quantitative PCR for its speed, sensitivity, specificity and ease-of-use. However, quantitative PCR quantitation requires the use of a standard curve or normalisation to reference genes. Droplet digital PCR provides absolute quantitation without the need for calibration curves. A comparison between droplet digital PCR and quantitative PCR-based analyses was conducted for the enteric parasite Cryptosporidium, which is an important cause of gastritis in both humans and animals. Two loci were analysed (18S rRNA and actin) using a range of Cryptosporidium DNA templates, including recombinant plasmids, purified haemocytometer-counted oocysts, commercial flow cytometry-counted oocysts and faecal DNA samples from sheep, cattle and humans. Each method was evaluated for linearity, precision, limit of detection and cost. Across the same range of detection, both methods showed a high degree of linearity and positive correlation for standards (R(2)⩾0.999) and faecal samples (R(2)⩾0.9750). The precision of droplet digital PCR, as measured by mean Relative Standard Deviation (RSD;%), was consistently better compared with quantitative PCR, particularly for the 18S rRNA locus, but was poorer as DNA concentration decreased. The quantitative detection of quantitative PCR was unaffected by DNA concentration, but droplet digital PCR quantitative PCR was less affected by the presence of inhibitors, compared with quantitative PCR. For most templates analysed including Cryptosporidium-positive faecal DNA, the template copy numbers, as determined by droplet digital PCR, were consistently lower than by quantitative PCR. However, the quantitations obtained by quantitative PCR are dependent on the accuracy of the standard curve and when the quantitative PCR data were corrected for pipetting and DNA losses (as determined by droplet digital PCR), then the sensitivity of both methods was comparable. A cost analysis based on 96 samples revealed that the overall cost (consumables and labour) of droplet digital PCR was two times higher than quantitative PCR. Using droplet digital PCR to precisely quantify standard dilutions used for high-throughput and cost-effective amplifications by quantitative PCR would be one way to combine the advantages of the two technologies.

Enumerating Microorganism Surrogates for Groundwater Transport Studies Using Solid-Phase Cytometry

Investigations on the pollution of groundwater with pathogenic microorganisms, e.g. tracer studies for groundwater transport, are constrained by their potential health risk. Thus, microspheres are often used in groundwater transport studies as non-hazardous surrogates for pathogenic microorganisms. Even though pathogenic microorganisms occur at low concentrations in groundwater, current detection methods of microspheres (spectrofluorimetry, flow cytometry and epifluorescence microscopy) have rather high detection limits and are unable to detect rare events. Solid-phase cytometry (SPC) offers the unique capability of reliably quantifying extremely low concentrations of fluorescently labelled microorganisms or microspheres in natural waters, including groundwater. Until now, microspheres have been used in combination with SPC only for instrument calibration purposes and not for environmental applications. In this study, we explored the limits of the SPC methodology for its applicability to groundwater transport studies. The SPC approach proved to be a highly sensitive and reliable enumeration system for microorganism surrogates down to a minimum size of 0.5 μm, in up to 500 ml of groundwater, and 0.75 μm, in up to 1 ml of turbid surface water. Hence, SPC is proposed to be a useful method for enumerating microspheres for groundwater transport studies in the laboratory, as well as in the field when non-toxic, natural products are used.

Alternative indicators for monitoring Cryptosporidium oocysts in reclaimed water

With the widespread use of reclaimed water all over the world, there is a clear need to optimise its management in order to guarantee water safety. Model microorganisms (with either indicator or index function) are commonly used to assess risks related to the presence of enteric pathogens in water. Samples from five water reclamation plants located in Northeastern Spain were analysed to validate the use of three model microorganisms (Escherichia coli, somatic coliphages and spores of sulphite-reducing clostridia) as surrogates of Cryptosporidium total or infectious oocysts (TOO and IOO, respectively) in reclaimed water. Probability plots, simple and multiple linear regression and discriminant analyses were performed to assess their relationships. Results show that the detection of E. coli alone is not useful to model either the behaviour or concentrations of Cryptosporidium. However, discriminant analyses showed a high rate of correctly classified samples (91.9%) when E. coli and somatic coliphages data were used together to predict the presence/absence of IOO. Spores of sulphite-reducing clostridia (SRC) showed parallel reduction patterns and high correlation values (r = 0.76) with reductions in TOO. Furthermore, simple regression analyses of SRC and TOO in reclaimed water showed high correlation values (r = 0.85). Therefore, at the treatment plants studied, SRC can be considered to have good indicator and index functions for TOO. From the point of view of health protection, the use of SRC together with E. coli (which is mandatory in the current Spanish regulations) would satisfy the need for improved reclaimed water management.

The concentration of Cryptosporidium and Giardia in water--the role and importance of recovery efficiency

The concentration of Cryptosporidium and of Giardia in surface water is a subject of importance to public health and public water supply. The term concentration is a fundamental property of any water quality parameter having a classical definition as used in chemistry and biology. Analytical methods for measuring the occurrence of Cryptosporidium and Giardia in water find only a fraction of the organisms actually present. This paper collects recently available data to examine the role and importance of recovery efficiency measurement to description of the concentrations of these organisms. Data from Australian sources graphically illustrate the variability of recovery efficiency at individual sites over relatively short time scales. Additional data on replicated recovery measurements establish their reproducibility. The recently released USEPA LT2 data along with those from Australia illustrate the independent variation of Cryptosporidium and Giardia occurrence and recovery efficiency at individual sampling locations. Calculation of concentration from paired raw numbers and recovery efficiency measurements clearly shows the magnitude and importance of taking recovery into account in expressing the concentration of these organisms.

Intensive exploitation of a karst aquifer leads to Cryptosporidium water supply contamination

Groundwater from karst aquifers is an important source of drinking water worldwide. Outbreaks of cryptosporidiosis linked to surface water and treated public water are regularly reported. Cryptosporidium oocysts are resistant to conventional drinking water disinfectants and are a major concern for the water industry. Here, we examined conditions associated with oocyst transport along a karstic hydrosystem, and the impact of intensive exploitation on Cryptosporidium oocyst contamination of the water supply. We studied a well-characterized karstic hydrosystem composed of a sinkhole, a spring and a wellbore. Thirty-six surface water and groundwater samples were analyzed for suspended particulate matter, turbidity, electrical conductivity, and Cryptosporidium and Giardia (oo)cyst concentrations. (Oo)cysts were identified and counted by means of solid-phase cytometry (ChemScan RDI(®)), a highly sensitive method. Cryptosporidium oocysts were detected in 78% of both surface water and groundwater samples, while Giardia cysts were found in respectively 22% and 8% of surface water and groundwater samples. Mean Cryptosporidium oocyst concentrations were 29, 13 and 4/100 L at the sinkhole, spring and wellbore, respectively. Cryptosporidium oocysts were transported from the sinkhole to the spring and the wellbore, with respective release rates of 45% and 14%, suggesting that oocysts are subject to storage and remobilization in karst conduits. Principal components analysis showed that Cryptosporidium oocyst concentrations depended on variations in hydrological forcing factors. All water samples collected during intensive exploitation contained oocysts. Control of Cryptosporidium oocyst contamination during intensive exploitation is therefore necessary to ensure drinking water quality.

CONTROLE DE QUALIDADE ANALÍTICA DOS MÉTODOS UTILIZADOS PARA A DETECÇÃO DE PROTOZOÁRIOS PATOGÊNICOS EM AMOSTRAS DE ÁGUA

RESUMO As espécies de protozoários patogênicos de veiculação hídrica Giardia spp. e Cryptosporidium spp. foram responsáveis por cerca 90% dos surtos de gastroenterite ocorridos nos últimos 25 anos, em vários países. Critérios de avaliação das etapas referentes à detecção destes agentes em amostras de água, tais como: precisão inicial, inoculação nas amostras em água bruta e, diagnóstico e localização de erros estão abordados neste trabalho. Estes critérios devem ser correntemente aplicados e constantemente avaliados pelos laboratórios, a fim de assegurar a confiabilidade dos resultados obtidos durante um monitoramento e, assim, fornecer subsídios para uma avaliação do risco de surtos.

Quantification of analytical recovery in particle and microorganism enumeration methods

Enumeration-based methods that are often used to quantify microorganisms and microscopic discrete particles in aqueous systems may include losses during sample processing or errors in counting. Analytical recovery (the capacity of the analyst to successfully count each microorganism or particle of interest in a sample using a specific enumeration method) is frequently assessed by enumerating samples that are seeded with known quantities of the microorganisms or particles. Probabilistic models were developed to account for the impacts of seeding and analytical error on recovery data, and probability intervals, obtained by Monte Carlo simulation, were used to evaluate recovery experiment design (i.e., seeding method, number of seeded particles, and number of samples). The method of moments, maximum likelihood estimation, and credible intervals were used to statistically analyze recovery experiment results. Low or uncertain numbers of seeded particles were found to result in variability in recovery data that was not due to analytical recovery, and should be avoided if possible. This additional variability was found to reduce the reproducibility of experimental results and necessitated the use of statistical analysis techniques, such as maximum likelihood estimation using probabilistic models that account for the impacts of sampling and analytical error in recovery data.

Cryptosporidium: detection in water and food

Water and food are major environmental transmission routes for Cryptosporidium, but our ability to identify the spectrum of oocyst contributions in current performance-based methods is limited. Determining risks in water and foodstuffs, and the importance of zoonotic transmission, requires the use of molecular methods, which add value to performance-based morphologic methods. Multi-locus approaches increase the accuracy of identification, as many signatures detected in water originate from species/genotypes that are not infectious to humans. Method optimisation is necessary for detecting small numbers of oocysts in environmental samples consistently, and further work is required to (i) optimise IMS recovery efficiency, (ii) quality assure performance-based methods, (iii) maximise DNA extraction and purification, (iv) adopt standardised and validated loci and primers, (v) determine the species and subspecies range in samples containing mixtures, and standardising storage and transport matrices for validating genetic loci, primer sets and DNA sequences.

Evaluation of the efficacy of immunomagnetic separation for the detection of Clavibacter michiganensis subsp. michiganensis in tomato seeds

AIMS

To evaluate the effectiveness of the optimized immunomagnetic separation (IMS)-plating protocol in relation to other culture, serological and molecular techniques currently used for Clavibacter michiganensis subsp. michiganensis in seed-testing laboratories.

METHODS AND RESULTS

Bacterial suspensions, tomato seed extracts spiked with the pathogen and naturally infected seeds were IMS-plated for the detection of C. m. subsp. michiganensis. These results were compared with plating on general (YPGA) and semiselective (mSCM) media, double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), immunofluorescent assay (IF) or polymerase chain reaction (PCR). Different seed lots and pathogen strains were also tested. IMS-plating allowed the detection of less than 10 CFU ml(-1) of pathogen in all assayed samples. The mSCM medium provided positive results for 10 CFU ml(-1) in naturally infected seeds, but up to 14 days was necessary for the typical colonies of the target to be come visible. By serological techniques, 10(3) and up to 10(4) CFU ml(-1) were detected by IF and ELISA, respectively. DNA extraction was required to obtain positive results by PCR in seed extracts containing 10(3) CFU ml(-1) or more.

CONCLUSIONS

Among the evaluated methods, IMS-plating provided the best results regarding sensitivity and specificity for C. m. subsp. michiganensis detection, allowing the recovery of viable bacteria from seed extracts.

SIGNIFICANCE AND IMPACT OF THE STUDY

IMS-plating increases isolation rates of C. m. subsp. michiganensis and could improve standard protocols currently used for routine analysis.

Comparative study between two laser scanning cytometers and epifluorescence microscopy for the detection ofCryptosporidium oocysts in water

BACKGROUND

Cryptosporidium detection in water and environmental samples has increased during the last years, largely due to an increase in the number of reported waterborne outbreaks of cryptosporidiosis and the implementation of new regulations about Cryptosporidium monitoring in water supplies. The aim of this study was to validate and compare the capacity of two laser scanning cytometers commercially available (LSC and ChemScanRDI), against manual microscopic enumeration of Cryptosporidium oocysts in surface water and reference material samples.

METHODS

Reference material and surface water samples were analysed by two laser scanning cytometers methodologies and by manual epifluorescence microscopy. Two mAbs from commercial suppliers were used to evaluate background reduction.

RESULTS

Highly significant correlations were obtain between both cytometers (R(2) = 0.99) and with manual microscopy (R(2) = 0.98), showing that oocysts counts made by cytometers were equivalent to those obtained with conventional methods. We observed a variability in oocysts counts when different antibodies where used with laser scanning cytometers and manual microscopy.

CONCLUSIONS

This study showed the efficacy of the laser scanning technology (LSC and ChemScanRDI), as an automated and a more standardized alternative to manual epifluorescence microscopy examination, for Cryptosporidium detection in water samples. High quality antibodies are needed for automated enumeration as well as for manual microscope observations.

Direct counting of Cryptosporidium parvum oocysts using fluorescence in situ hybridization on a membrane filter

This report describes the development of a direct and rapid detection method for the pathogenic protozoan, Cryptosporidium parvum, from environmental water samples using fluorescence in situ hybridization (FISH) on a membrane filter. The hydrophilic polytetrafluoroethylene (PTFE) membrane filter with FISH-stained oocysts yielded the highest signal to noise (S/N) ratio of the different membrane filters tested. PTFE membranes retained 98.8+/-0.4% of the concentrated oocysts after washing, simultaneous permeabilization and fixation with a hot ethanol solution, and hybridization with a fluorescently labeled oligonucleotide probe. This procedure eliminates subsequent time-consuming recovery steps that often result in a loss of the actual oocysts in a given environmental water sample. Furthermore, C. parvum was successfully distinguished from Cryptosporidium muris and other species in environmental water samples with the addition of formamide into the hybridization solution. In tap water samples, the S/N ratio was heightened by washing the membrane filter prior to FISH with a 1 M HCl solution in order to reduce the large amounts of impurities and background fluorescence from the non-specific adsorption of the fluorescently labeled oligonucleotide probe.

Molecular fingerprinting of Cryptosporidium oocysts isolated during water monitoring

We developed and validated a PCR-based method for identifying Cryptosporidium species and/or genotypes present on oocyst-positive microscope slides. The method involves removing coverslips and oocysts from previously examined slides followed by DNA extraction. We tested four loci, the 18S rRNA gene (N18SDIAG and N18SXIAO), the Cryptosporidium oocyst wall protein (COWP) gene (STN-COWP), and the dihydrofolate reductase (dhfr) gene (by multiplex allele-specific PCR), for amplifying DNA from low densities of Cryptosporidium parvum oocysts experimentally seeded onto microscope slides. The N18SDIAG locus performed consistently better than the other three tested. Purified oocysts from humans infected with C. felis, C. hominis, and C. parvum and commercially purchased C. muris were used to determine the sensitivities of three loci (N18SDIAG, STN-COWP, and N18SXIAO) to detect low oocyst densities. The N18SDIAG primers provided the greatest number of positive results, followed by the N18SXIAO primers and then the STN-COWP primers. Some oocyst-positive slides failed to generate a PCR product at any of the loci tested, but the limit of sensitivity is not entirely based on oocyst number. Sixteen of 33 environmental water monitoring Cryptosporidium slides tested (oocyst numbers ranging from 1 to 130) contained mixed Cryptosporidium species. The species/genotypes most commonly found were C. muris or C. andersoni, C. hominis or C. parvum, and C. meleagridis or Cryptosporidium sp. cervine, ferret, and mouse genotypes. Oocysts on one slide contained Cryptosporidium muskrat genotype II DNA.

The effects of time and temperature on flow cytometry enumerated live Cryptosporidium parvum oocysts

AIMS

Recoveries of spiked standard suspensions are used to evaluate method performance. For many applications, gamma-irradiated Cryptosporidium oocysts are appropriate. In contrast, methods that determine viability, such as Cryptosporidium cell culture, require the use of live oocysts. Oocyst standards are usually prepared at a flow cytometry laboratory for use at another laboratory, and thus the samples are shipped. The goal of this study was to evaluate the shipping and storage stability of flow cytometry enumerated live oocysts over time at three temperatures: 4 degrees C, room temperature and 37 degrees C.

METHODS AND RESULTS

Replicate samples containing 100 live C. parvum oocysts were prepared by flow cytometry and stored at 4 degrees C, room temperature and 37 degrees C. These samples were counted at various time points. Significant oocyst losses were observed after storage for 1 day at 37 degrees C, 7 days at room temperature and 21 days at 4 degrees C.

CONCLUSIONS

Live C. parvum oocysts internal standards should be used within 10 days of preparation, and stored and shipped at 4 degrees C.

SIGNIFICANCE AND IMPACT OF THE STUDY

When evaluating method performance with live oocysts, both the storage temperature and time are critical factors for obtaining reliable and accurate results.

Quantitative and qualitative comparison of density-based purification methods for detection of Cryptosporidium oocysts in turbid environmental matrices

Purification methods for Cryptosporidium oocysts are usually selected on the basis of recovery yield, but the amount of particulate debris in environmental matrices could limit efficiency of oocyst detection by microscopic examination or PCR detection. Previous studies have shown that the standard immunomagnetic separation (IMS) procedure would not be the most suitable method for oocyst purification from turbid matrices. We compared the capacity of Percoll-sucrose flotation and six other density-based purification methods to achieve selective separation of Cryptosporidium oocysts from particulate debris. Rate of oocyst recovery and particulate loading in the purified suspensions were chosen as comparison criteria for the different purification methods. In most earlier studies, the chemical treatments employed to obtain a purified oocyst suspension modify the surface properties of oocysts in spiked samples. Assuming this produces unrealistic conditions affecting the evaluation of purification methods, we performed the present study with native oocysts. Flotation and gradient procedures were tested with and without formaldehyde ethyl acetate (FEA) separation. FEA separation was found to be unsuitable. Filtration and Percoll gradient did not allow selective oocyst separation from debris. Among the purification methods suitable for routine microscopic examination, Percoll-sucrose flotation provided the best recovery rates. For automated enumeration systems or PCR detection, potassium bromide and especially Nycodenz gradients appeared to be the most suitable purification methods. Potassium bromide and Nycodenz gradients provided the best balance between oocyst recovery and particulate load.

Comparison of methods for the concentration ofCryptosporidiumoocysts andGiardiacysts from raw waters

This study compared the recovery of Cryptosporidium oocysts and Giardia cysts ((oo)cysts) from raw waters using 4 different concentration–elution methods: flatbed membranes, FiltaMaxTMfoam, EnvirochekTMHV capsules, and Hemoflow ultrafilters. The recovery efficiency of the combined immunomagnetic separation and staining steps was also determined. Analysis of variance of arcsine-transformed data demonstrated that recovery of Cryptosporidium oocysts by 2 of the methods was statistically equivalent (flatbed filtration 26.7% and Hemoflow 28.3%), with FiltaMaxTMand EnvirochekTMHV recoveries significantly lower (18.9% and 18.4%). Recovery of Giardia cysts was significantly higher using flatbed membrane filtration (42.2%) compared with the other 3 methods (EnvirochekTMHV 29.3%, FiltaMaxTM29.0%, and Hemoflow 20.9%). All methods were generally acceptable and are suitable for laboratory use; 2 of the methods are also suitable for field use (FiltaMaxTMand EnvirochekTMHV). In conclusion, with recoveries generally being statistically equivalent or similar, practical considerations become important in determining which filters to use for particular circumstances. The results indicate that while low-turbidity or "finished" waters can be processed with consistently high recovery efficiencies, recoveries from raw water samples differ significantly with variations in raw water quality. The use of an internal control with each raw water sample is therefore highly recommended.Key words: catchments, EnvirochekTMHV, Hemoflow, FiltaMaxTM, flatbed filtration.

Production of precise microbiology standards using flow cytometry and freeze drying

BACKGROUND

Quality control standards provide a quantity of microorganisms for routine use in microbiology to demonstrate the efficacy of testing methods and culture media. Standards are normally prepared by diluting a culture of microorganisms to obtain a suspension that contains an estimated number of colony-forming units per milliliter. The variability and inaccuracy of these standards increase the potential for false results. Flow cytometry has been used extensively to prepare precise standards of Cryptosporidium and Giardia that contain exact numbers of organisms in a volume of liquid (1). However, the same levels of accuracy have yet to be obtained for bacterial quality control standards.

METHODS

A modification of a Becton Dickinson FACScalibur flow cytometer enabled 30 bacterial cells to be sorted into a single droplet, mixed with a cryoprotective solution within the droplet, and frozen in liquid nitrogen. The frozen droplets were then freeze dried for stable preservation of the viable bacterial cells.

RESULTS

A freeze-dried sphere 3 mm in diameter was produced, which contained 30 microorganisms. The within-batch variation for these freeze-dried spheres was no greater than two standard deviations, and the between-batch variation was less than one standard deviation.

CONCLUSIONS

Bacterial reference controls can now be produced with consistent accuracy and unparalleled precision, thus enabling harmonization across the microbiological testing industry.

Evaluation of an internal positive control for Cryptosporidium and Giardia testing in water samples

AIMS

An internal positive control for Cryptosporidium and Giardia monitoring was evaluated for use in routine water monitoring quality control. The control, known as ColorSeed C&G (BTF Pty Ltd, Sydney, Australia), is a suspension containing exactly 100 Cryptosporidium oocysts and 100 Giardia cysts that have been modified by attachment of Texas Red to the cell wall, allowing them to be differentiated from unmodified oocysts and cysts. The control enables recovery efficiencies to be determined for every water sample analysed.

METHODS AND RESULTS

A total of 494 water samples were seeded with ColorSeed C&G and with unlabelled Cryptosporidium and Giardia and then analysed. Additionally, the robustness of the ColorSeed labelling was challenged with various chemical treatments. Recoveries were significantly lower for the ColorSeed Texas Red labelled Cryptosporidium and Giardia than recoveries of unlabelled Cryptosporidium and Giardia. However, the differences in recoveries were small. On average ColorSeed Cryptosporidium recoveries were 3.3% lower than unlabelled Cryptosporidium, and ColorSeed Giardia recoveries were 4% lower than unlabelled Giardia.

CONCLUSIONS

ColorSeed C&G is suitable for use as an internal positive control for routine monitoring of both treated and raw water samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

The small differences in recoveries are unlikely to limit the usefulness of ColorSeed C&G as an internal positive control. The ColorSeed labelling was found to be robust after different treatments.

Identification of Cryptosporidium spp. oocysts in United Kingdom noncarbonated natural mineral waters and drinking waters by using a modified nested PCR-restriction fragment length polymorphism assay

We describe a nested PCR-restriction fragment length polymorphism (RFLP) method for detecting low densities of Cryptosporidium spp. oocysts in natural mineral waters and drinking waters. Oocysts were recovered from seeded 1-liter volumes of mineral water by filtration through polycarbonate membranes and from drinking waters by filtration, immunomagnetizable separation, and filter entrapment, followed by direct extraction of DNA. The DNA was released from polycarbonate filter-entrapped oocysts by disruption in lysis buffer by using 15 cycles of freeze-thawing (1 min in liquid nitrogen and 1 min at 65 degrees C), followed by proteinase K digestion. Amplicons were readily detected from two to five intact oocysts on ethidium bromide-stained gels. DNA extracted from Cryptosporidium parvum oocysts, C. muris (RN 66), C. baileyi (Belgium strain, LB 19), human-derived C. meleagridis, C. felis (DNA from oocysts isolated from a cat), and C. andersoni was used to demonstrate species identity by PCR-RFLP after simultaneous digestion with the restriction enzymes DraI and VspI. Discrimination between C. andersoni and C. muris isolates was confirmed by a separate, subsequent digestion with DdeI. Of 14 drinking water samples tested, 12 were found to be positive by microscopy, 8 were found to be positive by direct PCR, and 14 were found to be positive by using a nested PCR. The Cryptosporidium species detected in these finished water samples was C. parvum genotype 1. This method consistently and routinely detected >5 oocysts per sample.

Application of laser scanning cytometry followed by epifluorescent and differential interference contrast microscopy for the detection and enumeration of Cryptosporidium and Giardia in raw and potable waters

AIMS

The main goal of this study was to validate a new laser scanning cytometry method (ChemScanRDI) that couples immunofluorescence detection with differential interference contrast (DIC) confirmation, against manual microscopic enumeration of Giardia and Cryptosporidium (oo)cysts. This study also assessed the basic performance of the new Association Française de Normalisation (AFNOR) NF T 90-455 method for Giardia and Cryptosporidium (oo)cyst enumeration with respect to (oo)cyst yield, linearity, repeatability, influence of turbidity and detection limit in raw and potable waters.

METHODS AND RESULTS

The new standard method relies on cartridge (Envirocheck) filtration, immunomagnetic separation purification, immunofluorescence staining and detection followed by DIC confirmation. The recovery was 30-50% for both parasites at seeding levels from 30 to 230 (oo)cysts. The method is linear from 0 to around 400 seeded (oo)cysts and the yield does not significantly vary for turbidity levels from 10 to 40 Formazin Nephelometric Units (FNU). The results were obtained using manual microscopic enumeration of the (oo)cysts. The ChemScanRDI yielded counts that were at least equivalent to those obtained using manual microscopy for both parasites in raw and potable water concentrates, for seeding levels of 10-300 or 10-100, respectively. The purification and labelling method proposed by the supplier of theChemScanRDI (Chemunex) reached very similar recoveries to the AFNOR protocol (70-86% in both cases).

CONCLUSIONS

Laser scanning cytometry can be used as a more standardized alternative to manual enumeration as part of the new AFNOR standard method.

SIGNIFICANCE AND IMPACT OF THE STUDY

By using laser scanning cytometry instead of manual microscopy, laboratories could circumvent the limitations of manual microscopy, namely: low sample throughput, operator subjectivity and operator fatigue. The study further supports the drive to incorporate laser scanning cytometry in the standard methods for Giardia and Cryptosporidium enumeration.

Optimised immunofluorescence procedure for enumeration of Cryptosporidium parvum oocyst suspensions

The aim of this study was to evaluate an optimised immunofluorescence assay in terms of the variability of sets of counts for Cryptosporidium parvum oocyst suspensions and data recovery and the reliability of the procedure. A coefficient of variation (CV) of 10% was determined to be the maximum value acceptable for count variability. It was found that the optimised IFA tested provided a high precision for the sets of enumerations for suspensions containing 800-20,000 oocysts/mL. The procedure was found to be robust and providing high recovery level (96.3%). In terms of counting precision, the technique described here approaches the performance of flow cytometry and surpasses other manual techniques with a CV of 10% for a concentration close to 800 oocysts/mL. The procedure described is particularly suitable for the production of seed doses and for other applications requiring the titration of oocyst suspensions with a high degree of precision and accuracy.

Immunomagnetic separation (IMS)-fluorescent antibody detection and IMS-PCR detection of seeded Cryptosporidium parvum oocysts in natural waters and their limitations

Detection and enumeration of Cryptosporidium parvum in both treated and untreated waters are important to facilitate prevention of future cryptosporidiosis incidents. Immunomagnetic separation (IMS)-fluorescent antibody (FA) detection and IMS-PCR detection efficiencies were evaluated in two natural waters seeded with nominal seed doses of 5, 10, and 15 oocysts. IMS-FA detected oocysts at concentrations at or below the three nominal oocyst seed doses, illustrating that IMS-FA is sensitive enough to detect low oocyst numbers. However, the species of the oocysts could not be determined with this technique. IMS-PCR, targeting the 18S rRNA gene in this study, yielded positive amplification for 17 of the 18 seeded water samples, and the amplicons were subjected to restriction fragment length polymorphism digestion and DNA sequencing for species identification. Interestingly, the two unseeded, natural water samples were also PCR positive; one amplicon was the same base pair size as the C. parvum amplicon, and the other amplicon was larger. These two amplified products were determined to be derived from DNA of Cryptosporidium muris and a dinoflagellate. These IMS-PCR results illustrate that (i) IMS-PCR is able to detect low oocyst numbers in natural waters, (ii) PCR amplification alone is not confirmatory for detection of target DNA when environmental samples are used, (ii) PCR primers, especially those designed against the rRNA gene region, need to be evaluated for specificity with organisms closely related to the target organism, and (iv) environmental amplicons should be subjected to appropriate species-specific confirmatory techniques.

Flow cytometry in oceanography 1989--1999: environmental challenges and research trends

BACKGROUND

The present review is based on the identification of four major environmental crises that have been approached from a biological oceanographic viewpoint. These crises are the release of contaminants in near shore marine waters, the collapse of marine resources that were renewable until recently, the loss of biodiversity, and global climate change

METHODS

The review examines the contribution of cytometry-based biological oceanography to the resolution of the four environmental crises. Using a database of 302 papers, flow cytometric (FCM) studies in biological oceanography over the 1989--1999 decade are examined. Future biological oceanographic applications of FCM are discussed.

RESULTS

Most of the published FCM oceanographic studies focus on phytoplankton and bacterioplankton. Analysis of our 1989-1999 database shows the predominance of studies dedicated to phytoplankton (77%), followed by heterotrophic bacteria (21%). The latter progressively increased over the last decade, together with the improved understanding of the biogeochemical and trophic roles of marine bacteria. Most studies on these two microorganisms were conducted in vitro until 1996, after which the trend reversed in favor of in situ research. The most investigated areas were those with major international sampling efforts, related to the changing climate. Concerning environmental topics, 62% of papers on phytoplankton and bacterioplankton focused on the structure of microbial communities and fluxes (e.g., production, grazing); this provides the basis for biological oceanographic studies on resources and climate change.

CONCLUSIONS

Future progress in the biological oceanographic use of FCM will likely fall into two categories, i.e., applications where FCM will be combined with the development of other methods and those where FCM will be the main analytical tool. It is expected that FCM and other cytometric approaches will improve the ability of biological oceanography to address the major environmental challenges that are confronting human societies.

Use of fluorescent probes to assess physiological functions of bacteria at single-cell level

A wide diversity of fluorescent probes is currently available to assess the physiological state of microorganisms. The recent development of techniques such as solid-phase cytometry, the increasing sensitivity of fluorescence tools and multiparametric approaches combining taxonomic and physiological probes have improved the effectiveness of direct methods in environmental and industrial microbiology.

Comparison of Cryptosporidium parvum viability and infectivity assays following ozone treatment of oocysts

Several in vitro surrogates have been developed as convenient, user-friendly alternatives to mouse infectivity assays for determining the viability of Cryptosporidium parvum oocysts. Such viability assays have been used increasingly to determine oocyst inactivation following treatment with chemical, physical, or environmental stresses. Defining the relationship between in vitro viability assays and oocyst infectivity in susceptible hosts is critical for determining the significance of existing oocyst inactivation data for these in vitro assays and their suitability in future studies. In this study, four viability assays were compared with mouse infectivity assays, using neonatal CD-1 mice. Studies were conducted in the United States and United Kingdom using fresh (<1 month) or environmentally aged (3 months at 4 degrees C) oocysts, which were partially inactivated by ozonation before viability and/or infectivity analyses. High levels of variability were noted within and between the viability and infectivity assays in the U.S. and United Kingdom studies despite rigorous control over oocyst conditions and disinfection experiments. Based on the viability analysis of oocyst subsamples from each ozonation experiment, SYTO-59 assays demonstrated minimal change in oocyst viability, whereas 4',6'-diamidino-2-phenylindole-propidium iodide assays, in vitro excystation, and SYTO-9 assays showed a marginal reduction in oocyst viability. In contrast, the neonatal mouse infectivity assay demonstrated significantly higher levels of oocyst inactivation in the U.S. and United Kingdom experiments. These comparisons illustrate that four in vitro viability assays cannot be used to reliably predict oocyst inactivation following treatment with low levels of ozone. Neonatal mouse infectivity assays should continue to be regarded as a "gold standard" until suitable alternative viability surrogates are identified for disinfection studies.