Computer-Assisted Laser Scanning and Video Microscopy for Analysis of Cryptosporidium parvum Oocysts in Soil, Sediment, and Feces

Comparison of current methods used to detect Cryptosporidium oocysts in stools

In this review all of the methods that are currently in use for the investigation of Cryptosporidium in stool material are highlighted and critically discussed. It appears that more qualifications and background knowledge in this field regarding the diagnosis of the Cryptosporidium parasite is required. Furthermore, there is no standardization for the protocols that are commonly used to either detect oocysts in faeces or to diagnose the Cryptosporidium infection. It is therefore necessary to initiate further education and research that will assist in improving the accuracy of the diagnosis of Cryptosporidium oocysts in the faecal micro-cosmos. Where ambient concentrations of oocysts are low in stool material, detection becomes a formidable task. Procedures for ring tests and the standardization of multi-laboratory testing are recommended. It is also necessary to enhance the routine surveillance capacity of cryptosporidiosis and to improve the safety against it, considering the fact that this disease is under diagnosed and under reported. This review is intended to stimulate research that could lead to future improvements and further developments in monitoring the diagnostic methodologies that will assist in harmonizing Cryptosporidium oocysts in stool diagnosis.

An overview of methods/techniques for the detection of Cryptosporidium in food samples

Cryptosporidium is one of the most important parasitic protozoa of concern within the food production industry, worldwide. This review describes the evolution and its development, and it monitors the methodology that has been used for Cryptosporidium in food material since 1984, when the first publication appeared regarding the detection of Cryptosporidium parvum in food materials. The methods that are currently being used for the detection of Cryptosporidium oocysts in food material (mainly vegetables) and all of the other available published methods are discussed in this review. Generating more consistent and reliable data should lead to a better understanding of the occurrence, transport and fate of the oocysts in food material. Improvements in monitoring and developing effective methodology, along with food security, offer more practical possibilities for both the developed and developing worlds.

Point-of-Use Removal of Cryptosporidium parvum from Water: Independent Effects of Disinfection by Silver Nanoparticles and Silver Ions and by Physical Filtration in Ceramic Porous Media

Ceramic water filters (CWFs) impregnated with silver nanoparticles are a means of household-level water treatment. CWFs remove/deactivate microbial pathogens by employing two mechanisms: metallic disinfection and physical filtration. Herein we report on the independent effects of silver salt and nanoparticles on Cryptosporidium parvum and the removal of C. parvum by physical filtration in porous ceramic filter media. Using a murine (mouse) model, we observed that treatment of oocysts with silver nitrate and proteinate-capped silver nanoparticles resulted in decreased infection relative to untreated oocysts. Microscopy and excystation experiments were conducted to support the disinfection investigation. Heat and proteinate-capped silver-nanoparticle treatment of oocysts resulted in morphological modifications and decreased excystation rates of sporozoites. Subsequently, disk-shaped ceramic filters were produced to investigate the transport of C. parvum. Two factors were varied: sawdust size and clay-to-sawdust ratio. Five disks were prepared with combinations of 10, 16, and 20 mesh sawdust and sawdust percentage that ranged from 9 to 11%. C. parvum removal efficiencies ranged from 1.5 log (96.4%) to 2.1 log (99.2%). The 16-mesh/10% sawdust had the greatest mean reduction of 2.1-log (99.2%), though there was no statistically significant difference in removal efficiency. Based on our findings, physical filtration and silver nanoparticle disinfection likely contribute to treatment of C. parvum for silver impregnated ceramic water filters, although the contribution of physical filtration is likely greater than silver disinfection.

Correlation between diarrhea severity and oocyst count via quantitative PCR or fluorescence microscopy in experimental cryptosporidiosis in calves

Cryptosporidium is an important diarrhea-associated pathogen, however the correlation between parasite burden and diarrhea severity remains unclear. We studied this relationship in 10 experimentally infected calves using immunofluorescence microscopy and real-time polymerase chain reaction (qPCR) (N = 124 fecal samples). The qPCR data were corrected for extraction/amplification efficiency and gene copy number to generate parasite counts. The qPCR and microscopic oocyst quantities exhibited significant correlation (R(2) = 0.33, P < 0.05), however qPCR had increased sensitivity. Upon comparison with diarrhea severity scores (from 0 to 3), a PCR-based count of ≥ 2.6 × 10(5) parasites or an immunofluorescence microscopy count of ≥ 4.5 × 10(4) oocysts were discriminatory predictors of moderate-to-severe diarrhea (versus no-to-mild diarrhea), with accuracies and predictive values of 72-82%. In summary, a quantitative approach for Cryptosporidium can refine predictive power for diarrhea and appears useful for distinguishing clinical cryptosporidiosis versus subclinical infection.

Investigation of microbial biofilm structure by laser scanning microscopy

Microbial bioaggregates and biofilms are hydrated three-dimensional structures of cells and extracellular polymeric substances (EPS). Microbial communities associated with interfaces and the samples thereof may come from natural, technical, and medical habitats. For imaging such complex microbial communities confocal laser scanning microscopy (CLSM) is the method of choice. CLSM allows flexible mounting and noninvasive three-dimensional sectioning of hydrated, living, as well as fixed samples. For this purpose a broad range of objective lenses is available having different working distance and resolution. By means of CLSM the signals detected may originate from reflection, autofluorescence, reporter genes/fluorescence proteins, fluorochromes binding to specific targets, or other probes conjugated with fluorochromes. Recorded datasets can be used not only for visualization but also for semiquantitative analysis. As a result CLSM represents a very useful tool for imaging of microbiological samples in combination with other analytical techniques.

Quantitative dielectrophoretic tracking for characterization and separation of persistent subpopulations of Cryptosporidium parvum

Microbial persistence to antibiotics is attributed to subpopulations with phenotypic variations that cause a spread of susceptibility levels, leading to the recurrence of infections and stability of biofilms. Herein, persistent oocyst subpopulations identified by animal infectivity and excystation assays during the disinfection of Cryptosporidium parvum, a water-borne pathogen capable of causing enteric infections at ultra-low doses, are separated and characterized by quantitative dielectrophoretic tracking over a wide frequency range (10 kHz-10 MHz). To enable the simultaneous and facile dielectrophoretic tracking of individual oocysts, insulator constrictions in a microfluidic channel are utilized to spatially modulate the localized field over the extent needed for defining oocyst trajectories and for obtaining high-resolution displacement versus time measurements under both, positive and negative dielectrophoresis. In this manner, by obviating the need for averaging dielectrophoretic data over a large collection region, the force response is more sensitive to differences in electrophysiology from sub-population fractions. Hence, the electrophysiology of sensitive and persistent oocysts after heat and silver nanoparticle treatments can be quantified by correlating the force response at low frequencies (<100 kHz) to the integrity of the oocyst wall and at high frequencies (0.4-1 MHz) to the sporozoites in the oocyst. This label-free method can characterize heterogeneous microbial samples with subpopulations of phenotypically different alterations, for quantifying the intensity of alteration and fraction with a particular alteration type.

Cryptosporidium parvum: determination of ID₅₀ and the dose-response relationship in experimentally challenged dairy calves

The objectives were to determine the median infective dose (ID₅₀) of Cryptosporidium parvum and to describe the dose–response relationship including associated clinical illness in experimentally challenged dairy calves. Within the first 24 h of life, 27 test calves were experimentally challenged with C. parvum oocysts and 3 control calves were sham dosed. Test calves received 1 of 8 possible doses (25, 50, 100, 500, 1 × 10³, 1 × 10⁴, 1 × 10⁵, and 1 × 10⁶ oocysts). All 27 test calves developed diarrhea. Fecal oocyst shedding occurred in 25 (92.6%) test calves and in 0 control calves. The 2 non-shedding test calves both received 25 oocysts. There was an inverse relationship between dose and time to onset of fecal oocyst shedding (P = 0.005). There was no relationship found between dose and duration (P = 0.2) or cessation (P = 0.3) of fecal oocyst shedding. In addition, there was not a significant relationship between log-dose and the log-peak oocysts (P = 0.2) or log-total oocysts (P = 0.5) counted/g of feces across the dose groups. There was a positive dose–response relationship between log-dose and diarrhea (P = 0.01). However, when controlling for other factors, such as onset and cessation of fecal oocyst shedding, dose was not a significant predictor of diarrhea (P = 0.5). Onset and cessation of fecal oocyst shedding were found to be the best predictors of diarrhea (P = 0.0006 and P = 0.04, respectively). The ID₅₀ for fecal oocyst shedding was 5.8 oocysts, for diarrhea was 9.7 oocysts, and for fecal oocyst shedding with diarrhea was 16.6 oocysts. Given that the ID₅₀ of C. parvum is far less than would be excreted into the environment by a naturally infected calf, prevention and control of cryptosporidiosis is a formidable challenge.

Description of fecal shedding of Cryptosporidium parvum oocysts in experimentally challenged dairy calves

The objective was to describe the probability of Cryptosporidium parvum fecal oocyst shedding at different magnitudes of exposure, the pattern of fecal shedding over time, and factors affecting fecal shedding in dairy calves. Within the first 24 h of life, 36 calves were experimentally challenged with C. parvum oocysts at one of four possible magnitudes of oral exposure (1 × 10³, 1 × 10⁴, 1 × 10⁵, and 1 × 10⁶ oocysts), and 7 control calves were sham dosed. Fecal shedding occurred in 33 (91.7 %) experimentally challenged calves and in none of the control calves. There was a difference in the log-total number of oocysts counted per gram of feces dry weight among the four exposure groups; calves with the lowest magnitude of exposure (1 × 10³ oocysts) shed less than the other three groups. At higher magnitudes of exposure, there was more variability in the range of fecal oocyst shedding. There was an inverse relationship between the log-total amount of oocysts counted per gram of feces dry weight and the number of days to the onset of fecal shedding per calf, i.e., the more time that elapsed to the onset of fecal shedding, the fewer oocysts that were shed. The pattern of fecal shedding over time for all calves shedding oocysts was curvilinear; the number of oocysts increased with time, reached a peak, and declined. Therefore, the dynamics of oocyst shedding can be influenced in part by limiting exposure among calves and delaying the onset of fecal oocyst shedding.

A comparison of fecal percent dry matter and number of Cryptosporidium parvum oocysts shed to observational fecal consistency scoring in dairy calves

Evaluation of dairy calf feces is often used in research and for clinical decision making to assess severity of diarrhea. However, this has not been validated for agreement between dry matter content and observed fecal consistency. Therefore, a comparison of observed fecal consistency score to fecal percent dry matter and Cryptosporidium parvum oocyst shedding was performed to assess the accuracy of observational scoring as a measure of diarrhea and its association with number of oocysts shed. Fecal samples from 20 dairy calves experimentally infected with C. parvum oocysts were collected daily post-infection and scored on a scale from 1 to 4, with 1 being normal feces to 4 being severe diarrhea. An aliquot of each sample was analyzed for percent dry matter and Cryptosporidium oocyst counts by using immunofluorescent microscopy. Fecal consistency scores of 1, 2, 3, and 4 had median percent dry matter of 20.9, 16.3, 9.6, and 5.8, respectively. Using percent dry matter assessed by fecal consistency scoring were significantly different from each other (P < 0.001). A higher fecal consistency score also was associated with a greater number of Cryptosporidium oocysts shed (P < 0 .0001). Scores of 1, 2, 3, and 4 had median oocyst counts of 0, 0, 1.3 × 10⁶, and 2.8 × 10⁶, respectively. These results suggest that observational scoring is a useful proxy to assess diarrhea in dairy calves.

Concentrations, viability, and distribution of Cryptosporidium genotypes in lagoons of swine facilities in the Southern Piedmont and in coastal plain watersheds of Georgia

Waste lagoons of swine operations are a source of Cryptosporidium oocysts. Few studies, however, have reported on oocyst concentrations in swine waste lagoons; none have reported on oocyst viability status, nor has there been a systematic assessment of species/genotype distributions across different types of swine facilities. Ten swine waste lagoons associated with farrowing, nursery, finishing, and gestation operations were each sampled once a month for a year. Oocysts were extracted from triplicate 900-ml effluent samples, enumerated by microscopy, and assessed for viability by dye exclusion/vital stain assay. DNA was extracted from processed samples, and 18S ribosomal DNA (rDNA) genes were amplified by PCR and sequenced for species and genotype identification. Oocysts were observed at each sampling time at each lagoon. Annual mean concentrations of total oocysts and viable oocysts ranged between 24 and 51 and between 0.6 and 12 oocysts ml(-1) effluent, respectively. The species and genotype distributions were dominated (95 to 100%) by Cryptosporidium suis and Cryptosporidium pig genotype II, the latter of which was found at eight of the lagoons. The lagoon at the gestation facility was dominated by Cryptosporidium muris (90%), and one farrowing facility showed a mix of pig genotypes, Cryptosporidium muris, and various genotypes of C. parvum. The zoonotic C. parvum bovine genotype was observed five times out of 407 18S rDNA sequences analyzed. Our results indicate that pigs can have mixed Cryptosporidium infections, but infection with C. suis is likely to be dominant.

Significance of wall structure, macromolecular composition, and surface polymers to the survival and transport of Cryptosporidium parvum oocysts

The structure and composition of the oocyst wall are primary factors determining the survival and hydrologic transport of Cryptosporidium parvum oocysts outside the host. Microscopic and biochemical analyses of whole oocysts and purified oocyst walls were undertaken to better understand the inactivation kinetics and hydrologic transport of oocysts in terrestrial and aquatic environments. Results of microscopy showed an outer electron-dense layer, a translucent middle layer, two inner electron-dense layers, and a suture structure embedded in the inner electron-dense layers. Freeze-substitution showed an expanded glycocalyx layer external to the outer bilayer, and Alcian Blue staining confirmed its presence on some but not all oocysts. Biochemical analyses of purified oocyst walls revealed carbohydrate components, medium- and long-chain fatty acids, and aliphatic hydrocarbons. Purified walls contained 7.5% total protein (by the Lowry assay), with five major bands in SDS-PAGE gels. Staining of purified oocyst walls with magnesium anilinonaphthalene-8-sulfonic acid indicated the presence of hydrophobic proteins. These structural and biochemical analyses support a model of the oocyst wall that is variably impermeable and resistant to many environmental pressures. The strength and flexibility of oocyst walls appear to depend on an inner layer of glycoprotein. The temperature-dependent permeability of oocyst walls may be associated with waxy hydrocarbons in the electron-translucent layer. The complex chemistry of these layers may explain the known acid-fast staining properties of oocysts, as well as some of the survival characteristics of oocysts in terrestrial and aquatic environments. The outer glycocalyx surface layer provides immunogenicity and attachment possibilities, and its ephemeral nature may explain the variable surface properties noted in oocyst hydrologic transport studies.

Changes of physical and biochemical properties of Cryptosporidium oocysts with various storage conditions

Physical and biochemical properties of Cryptosporidium parvum oocyst were examined after storage under various conditions. Oocyst-positive-fecal samples recovered from calves were either stored in a 2.0% potassium dichromate solution (Cr) or deionized water (W), or kept as a fecal pellet (P), and stored at 4 or 18 degrees C for a maximum of 100 days. When stored in Cr at 4 degrees C, the morphology of oocysts and their ability to withstand ultrasonics was not affected by the storing media or the storage period. However, when stored at 18 degees C as a fecal pellet, the specific gravity of the oocysts increased and a significant decrease in the oocysts resistance to ultrasonics occurred. These changes in oocyst properties may affect the performance of methods used to detect oocysts in water samples. When using the current test methods or when developing a new test method, it is important to take these factors into consideration.

Impacts of viability and purification on the specific gravity of Cryptosporidium oocysts

The specific gravity of unpurified and purified Cryptosporidium oocysts was measured using an isopycnic gradient centrifugation technique. Specific gravity varied depending on the viability of the oocysts, as defined by permeabilty to 4',6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI), the presence or absence of internal structures, and whether or not oocysts were purified. The modal range of densities for a population of 1.4-week-old unpurified oocysts, was 1070-1073 kg/m3. This range was higher than that determined for 14-week-old purified oocysts, 1067-1070 kg/m3. Eleven- and 12-week-old unpurified populations exhibited a bimodal distribution of densities, with densities most frequently in the 1005-1041 and in the 1077-1108 kg/m3 range. In these populations, a high percentage of the oocysts having densities greater than 1077 kg/m3 were viable, while oocysts in the 1005-1024 kg/m3 range were predominately nonintact, and oocysts in the 1024-1041 kg/m3 range were intact, but permeable to DAPI and PI (nonviable). This work demonstrates the importance of controlling factors that may impact the viability of oocysts when conducting studies that examine the transport of these microorganisms in the environment and through water treatment processes.

Settling behavior of unpurified Cryptosporidium oocysts in laboratory settling columns

The settling behavior of fresh and aged unpurified oocysts was examined in settling column suspensions with varied ionic strengths and concentrations of calcium and magnesium. Independent measurements of the size and density of unpurified oocysts were performed to determine a theoretical settling velocity for the test populations. Viability of the oocysts was assessed using a dye permeability assay. Latex microspheres were included to provide a standard by which to assess the settling conditions in the columns. Mean settling velocities for viable oocysts measured in this work were faster than predicted and faster than measured for purified oocysts in other work: 1.31 (+/-0.21) microm/s for viable oocysts from populations having a low percentage of viable oocysts and 1.05 (+/-0.20) microm/s for viable oocysts from populations with a high percentage of viable oocysts. Results were attributed to the higher than previously reported densities measured for oocysts in this study and the presence of fecal material, which allowed opportunity for particle agglomeration. Settling velocity of oocysts was significantly related to the viability of the population, particle concentration, ionic strength, and presence of calcium and magnesium in the suspending medium. Behavior of the latex microspheres was not entirely predictive of the behavior of the oocysts under the test conditions. Viable oocysts may have a greater probability of settling than previously assumed; however, nonviable, and especially nonintact, oocysts have the potential to be significantly transported in water. This work underscores the importance of assessing the viability of oocysts to predict their response to environmental and experimental conditions.

Effects of the Norwegian winter environment on Giardia cysts and Cryptosporidium oocysts

The structural integrity of Cryptosporidium oocysts and Giardia cysts in the Norwegian winter environment was investigated. During winter 2001/2002, Cryptosporidium oocysts and Giardia cysts were placed in the upper layers of soil in different matrices contained in chambers and exposed to the Norwegian climate. Morphological characteristics and inclusion/exclusion of vital dyes were monitored and compared to refrigerated controls. Reduction in parasite numbers was recorded for all parasites, geographical locations, and matrices. Shear forces generated during freeze-thaw cycles are postulated to have disintegrated the parasites exposed to the Norwegian winter and retrospective laboratory studies support this theory. Increased dye inclusion, possibly indicative of viability loss, was also noted. The refrigerated control parasites exhibited no decline in numbers, and alteration in dye inclusion characteristics for refrigerated parasites was slower. Cryptosporidium oocysts were apparently more robust than Giardia cysts; differences between isolates were also noted. These results suggest Cryptosporidium oocysts and Giardia cysts do not persist in the Norwegian terrestrial environment over winter, and when detected, will have been excreted since the previous winter. Differences in the morphological characteristics, matrix effects, and the possible relationship of the dye data to parasite survival are discussed in relation to further studies.

A new filter-eluting solution that facilitates improved recovery of Cryptosporidium oocysts from water

Cryptosporidium is a zoonotic coccidian parasite associated with diarrhea, and the disinfectant-resistant oocysts are threats to public health even in industrialized countries. In order to make an accurate assessment of the risk to public health, a detection method that has a high recovery rate of oocysts in water is required. In this study, we developed a new filter-eluting solution that facilitates more efficient recovery of Cryptosporidium oocysts from different kinds of water samples. The filter-eluting solution, referred to as PET, consists of sodium pyrophosphate (0.02%), Tween 80 (0.01%) and trisodium EDTA (0.03%). By using PET instead of conventional filter-eluting solutions, the average recovery rate significantly increased from 25.5+/-15.1% to 43.1+/-13.9% (p<0.05). The improved oocyst recovery was likely due to the increased separation of the oocysts from debris trapped on the filter membrane as well as increased capture of the oocysts by immunomagnetic beads. We recommend that PET be used as the filter-eluting solution for detection of Cryptosporidium oocysts in environmental water.

Assessment of methods for detection of infectious Cryptosporidium oocysts and Giardia cysts in reclaimed effluents

This study evaluates the occurrence of Cryptosporidium oocysts and Giardia cysts in reclaimed effluents if method 1623 with the Envirochek capsule filters (standard and high-volume [HV] filters) and a modified version of the Information Collection Rule method (ICR) with the polypropylene yarn-wound cartridge filter are used. The recovery efficiency of the analytical methods was evaluated with samples of reagent, tap, and reclaimed water by using flow cytometer-sorted spike suspensions. (Oo)cyst recovery efficiency determined filter performance and method reproducibility in the water matrix tested. Method 1623 with the Envirochek HV capsule filter generated significantly higher recovery rates than did the standard Envirochek filter and the modified ICR method. Notwithstanding, large variations in recovery rates (>80%) occurred with samples of reclaimed water, and none of the water quality parameters analyzed in the reclaimed effluents could explain such variability. The highest concentrations of indigenous oocysts were detected by method 1623 with the HV filter, which provided a sufficient number of oocysts for further confirmation of infectious potential. Confirmation of species and potential infectivity for all positive protozoan samples was made by using a nested PCR restriction fragment polymorphism assay and the focus detection method most-probable-number assay, respectively. The methodology and results described in the present investigation provide useful information for the establishment of pathogen numeric standards for reclaimed effluents used for unrestricted irrigation.

Recovery and enumeration of Cryptosporidium parvum from animal fecal matrices

Accurate quantification of Cryptosporidium parvum oocysts in animal fecal deposits on land is an essential starting point for estimating watershed C. parvum loads. Due to the general poor performance and variable recovery efficiency of existing enumeration methods, protocols were devised based on initial dispersion of oocysts from feces by vortexing in 2 mM tetrasodium pyrophosphate, followed by immunomagnetic separation. The protocols were validated by using an internal control seed preparation to determine the levels of oocyst recovery for a range of fecal types. The levels of recovery of 10(2) oocysts from cattle feces (0.5 g of processed feces) ranged from 31 to 46%, and the levels of recovery from sheep feces (0.25 g of processed feces) ranged from 21% to 35%. The within-sample coefficients of variation for the percentages of recovery from five replicates ranged from 10 to 50%. The ranges for levels of recovery of oocysts from cattle, kangaroo, pig, and sheep feces (juveniles and adults) collected in a subsequent watershed animal fecal survey were far wider than the ranges predicted by the validation data. Based on the use of an internal control added to each fecal sample, the levels of recovery ranged from 0 to 83% for cattle, from 4 to 62% for sheep, from 1 to 42% for pigs, and from 40 to 73% for kangaroos. Given the variation in the levels of recovery of oocysts from different fecal matrices, it is recommended that an internal control be added to at least one replicate of every fecal sample analyzed to determine the percentage of recovery. Depending on the animal type and based on the lowest approximate percentages of recovery, between 10 and 100 oocysts g of feces(-1) must be present to be detected.

Evaluation of attachment of Cryptosporidium parvum and Giardia lamblia to soil particles

Transport of Cryptosporidium parvum oocysts and Giardia lamblia cysts in the aquatic environment is poorly understood. Information about their transport is essential for actual risk assessment and development of effective control practices. Several studies have suggested that attachment to soil particles is not likely to occur, but the hypothesis has not been well tested, partly because enumeration of C. parvum oocysts or G. lamblia cysts [written as (oo)cysts] in the presence of soil has been difficult. In this paper, a combination of flow cytometry, and epifluorescence and confocal microscopy was successfully used to enumerate (oo)cysts in the presence of soil and determine whether (oo)cysts travel freely in water or attached to soil particles. The maximum soil concentration in water samples for reliable enumeration of (oo)cysts was 2 mg/L. Particle attachment experiments detected attached pairs of oppositely charged beads and (oo)cysts, while no attachment was observed between like charged beads, (oo)cysts, and soil particles. These results support the hypothesis that electrostatic forces govern the interaction between (oo)cysts and soil particles. Batch experiments further confirmed the null hypothesis (p > 0.05) that (oo)cysts do not attach to natural soil particles. These findings suggest that, when (oo)cysts have been entrained in overland flow (i.e., runoff), they will travel freely in the water and not as part of the particulate sediment load.

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.

Structure and carbohydrate analysis of the exopolysaccharide capsule of Pseudomonas putida G7

The aromatic hydrocarbon-degrading bacterium, Pseudomonas putida G7, produces exopolymers of potential interest in biotechnological applications. These exopolymers have been shown to have significant metal-binding ability. To initiate the study of the metal-polymer interactions, we explored the physical and chemical nature of the P. putida G7 exopolysaccharide, a major component of the exopolymer. A capsular structure was observed by light microscopy surrounding both planktonic and attached cells in biofilms after immunofluorescence staining with polyclonal antiserum raised against planktonic cells. Further work with planktonic cells showed that the immunostained capsule remained associated with young (log phase) cells, whereas older (stationary phase) cells lost their capsular material to the external milieu. Visualization of frozen, hydrated stationary phase cells by cryo-field emission scanning electron microscopy (cryoFESEM) revealed highly preserved extracellular material. In contrast, conventional scanning electron microscopy (SEM) of stationary phase cells showed rope-like material that most probably results from dehydrated and collapsed exopolymer. Both capsular and released exopolymers were separated from cells, and the released extracellular polysaccharide (EPS) was purified. Deoxycholate-polyacrylamide gel electrophoresis (PAGE) and silver/alcian blue staining of the partially purified material showed that it contained both EPS and lipopolysaccharide (LPS). Further purification of the EPS using a differential solubilization technique to remove LPS yielded highly purified EPS. Gas chromatography-mass spectrometry revealed that the purified EPS contained the monosaccharides, glucose, rhamnose, ribose, N-acetylgalactosamine and glucuronic acid. The structural and chemical properties of the P. putida EPS described here increase our understanding of the mechanisms of toxic metal binding by this well-known Proteobacterium.

Further biogeochemical characterization of a trichloroethene-contaminated fractured dolomite aquifer: electron source and microbial communities involved in reductive dechlorination

A recent article presented geochemical and microbial evidence establishing metabolic adaptation to and in-situ reductive dechlorination of trichloroethene (TCE) in a fractured dolomite aquifer. This study was designed to further explore site conditions and microbial populations and to explain previously reported enhancement of reductive dechlorination by the addition of pulverized dolomite to laboratory microcosms. A survey of groundwater geochemical parameters (chlorinated ethenes, ethene, H2, CH4, DIC, DOC, and delta13C values for CH4, DIC, and DOC) indicated that in situ reductive dechlorination was ongoing and that an unidentified pool of organic carbon was contributing, likely via microbial respiration, to the large and relatively light on-site DIC pool. Petroleum hydrocarbons associated with the dolomite rock were analyzed by GC/MS and featured a characteristically low delta13C value. Straight chain hydrocarbons were extracted from the dolomite previously found to stimulate reductive dechlorination; these were particularly depleted in hexadecane (HD). Thus, we hypothesized that HD and related hydrocarbons might be anaerobically respired and serve both as the source of on-site DIC and support reductive dechlorination of TCE. Microcosms amended with pulverized dolomite demonstrated reductive dechlorination, whereas a combusted dolomite amendment did not. HD-amended microcosms were also inactive. Therefore, the stimulatory factor in the pulverized dolomite was heat labile, but that component was not HD. Amplified Ribosomal DNA Restriction Analysis (ARDRA) of the microbial populations in well waters indicated that a relatively low diversity, sulfur-transforming community outside the plume was shifted toward a high diversity community including Dehalococcoides ethenogenes-type microorganisms inside the zone of contamination. These observations illustrate biogeochemical intricacies of in situ reductive dechlorination reactions.

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.

Chemical and physical factors affecting the excystation of Cryptosporidium parvum oocysts

Cryptosporidium parvum oocysts were examined to ascertain excystation requirements and the effects of gamma irradiation. Oocysts and excysted sporozoites were examined for dye permeability and infectivity. Maximum excystation occurred when oocysts were pretreated with acid and incubated with bile salts, and potassium or sodium bicarbonate. Pretreatment with Hanks' balanced salt solution or NaCl lowered excystation; however, this effect was overcome with acid. Sodium ions were replaceable with potassium ions, and sodium bicarbonate was replaceable with sodium phosphate. Oocysts that received 200 krad irradiation excysted at the same rates as nonirradiated oocysts (95%), the excystation rates were lowered (50%) by 2,000 krad, and no excystation was observed by 5,000 krad. No differences were observed between the propidium iodide (PI) permeability of untreated oocysts and oocysts treated with 200 krad, while 92% of oocysts were PI positive after 2,000 krad. Most of the sporozoites exposed to 2,000 krad were not viable as indicated by the dye permeability assay. The oocysts irradiated with 200 and 2,000 krad infected cells, but no replication was observed. The results suggest that gamma-irradiated oocysts may still be capable of excystation and apparent infection; however, because the sporozoites could not reproduce they must not have been viable.

Immunoassay for viable Cryptosporidium parvum oocysts in turbid environmental water samples

Cryptosporidium parvum oocysts in drinking water have been implicated in outbreaks of diarrheal disease. Current methods for monitoring environmental exposures to C. parvum only account for total number of oocysts without regard for the viability of the parasite. Measurement of oocyst viability, as indicated by an oocyst's ability to excyst, is useful because over time oocysts lose the ability to excyst and become noninfective. Thus, correlating the number of viable oocysts in drinking water with incidence and risk for disease should be more reliable than using the total number of oocysts. We have developed a quantitative assay capable of detecting low numbers of excystable, sporozoite-releasing C. parvum oocysts in turbid water samples. Monoclonal (CP7) and polyclonal antibodies have been developed against a sporozoite antigen released only during excystation or when the oocyst is mechanically disrupted. CP7 is specific for C. parvum and does not react with C. baileyi, C. muris, C. serpentis, Giardia spp., Eimeria spp., or E. nieschulzi. In this assay, oocysts in the test sample are first excysted and then centrifuged. The soluble sporozoite antigen is captured by CP7 attached to a magnetic bead. The captured antigen is then detected by ruthenium-labeled polyclonal antibodies via electrochemiluminescence. The CP7 viability assay can detect as few as 50 viable oocysts in a 1-ml assay sample with a turbidity as high as 200 Nephelometric turbidity units. This sensitive, turbidity-tolerant assay for oocyst viability may permit a better assessment of the disease risk associated with the presence of environmental oocysts.

Use of substrate responsive-direct viable counts to visualize naphthalene degrading bacteria in a coal tar-contaminated groundwater microbial community

A microscopy-based method was developed to distinguish naphthalene-degrading bacteria within the microbial community of a coal tar-contaminated groundwater system. Pure cultures of Pseudomonas putida NCIB 9816-4 were used to develop the substrate responsive-direct viable count (SR-DVC) method. Cells were concentrated on membrane filters, placed on agar plates of Stanier's minimal basal salts media containing antibiotics (nalidixic acid, piromidic acid, pipemidic acid, and cephalexin), and exposed to vapors of naphthalene. Following brief incubation, samples were fixed in 2% formaldehyde and examined by epifluorescent microscopy. Pure cultures displayed the expected cell elongation response to the SR-DVC assay and required a minimum incubation time of 9 h for differentiation of elongated cells. When applied to groundwater samples from the study site, naphthalene responsive cells in the groundwater community were easily distinguished from unresponsive cells and debris (350+/-180 substrate responsive cells/ml, relative to negative controls with no added growth substrate). In an attempt to reduce background counts of elongated bacteria and fungi, the SR-DVC procedure was modified by adding a wash step prior to incubation and a fungal inhibitor, cyclohexamide, to the plates. When groundwater samples were subjected to the modified procedure, only cells in washed samples showed a significant response to naphthalene (150+/-25 cells/ml), indicating the presence of inhibitory substances in the groundwater. Variations in response of the groundwater microbial community to the two SR-DVC procedures suggest that subsurface conditions (microbial and chemical composition) vary temporally. SR-DVC allows the phenotypes of individual naturally occurring cells to be assessed.

Epidemiology of Cryptosporidium: transmission, detection and identification

There are 10 valid species of Cryptosporidium and perhaps other cryptic species hidden under the umbrella of Cryptosporidium parvum. The oocyst stage is of primary importance for the dispersal, survival, and infectivity of the parasite and is of major importance for detection and identification. Because most oocysts measure 4-6 microm, appear nearly spherical, and have obscure internal structures, there are few or no morphometric features to differentiate species and in vitro cultivation does not provide differential data as for bacteria. Consequently, we rely on a combination of data from three tools: morphometrics, molecular techniques, and host specificity. Of 152 species of mammals reported to be infected with C. parvum or an indistinguishable organism, very few oocysts have ever been examined using more than one of these tools. This paper reviews the valid species of Cryptosporidium, their hosts and morphometrics; the reported hosts for the human pathogen, C. parvum; the mechanisms of transmission; the drinking water, recreational water, and food-borne outbreaks resulting from infection with C. parvum; and the microscopic, immunological, and molecular methods used to detect and identify species and genotypes.

Method for detection and enumeration of Cryptosporidium parvum oocysts in feces, manures, and soils

Eight concentration and purification methods were evaluated to determine percentages of recovery of Cryptosporidium parvum oocysts from calf feces. The NaCl flotation method generally resulted in the highest percentages of recovery. Based on the percentages of recovery, the amounts of fecal debris in the final oocyst preparations, the relatively short processing time (<3 h), and the low expense, the NaCl flotation method was chosen for further evaluation. Extraction efficiency was evaluated by using oocyst concentrations of 25, 50, 10(2), 10(3), 10(4), and 10(5) oocysts g of bovine feces-1. The percentages of recovery ranged from 10.8% (25 oocysts g-1) to 17.0% (10(4) oocysts g-1) (r2 = 0.996). A conservative estimate of the detection limit for bovine feces is ca. 30 oocysts g of feces-1. Percentages of recovery were determined for six different types of animal feces (cow, horse, pig, sheep, deer, and chicken feces) at a single oocyst concentration (10(4) oocysts g-1). The percentages of recovery were highest for bovine feces (17. 0%) and lowest for chicken feces (3.2%). Percentages of recovery were determined for bovine manure after 3 to 7 days of storage. The percentages of recovery ranged from 1.9 to 3.5% depending on the oocyst concentration, the time of storage, and the dispersing solution. The percentages of oocyst recovery from soils were evaluated by using different flotation solutions (NaCl, cold sucrose, ZnSO4), different dispersing solutions (Triton X-100, Tween 80, Tris plus Tween 80), different dispersion techniques (magnetic stirring, sonication, blending), and different dispersion times (5, 15, and 30 min). Twenty-five-gram soil samples were used to reduce the spatial variability. The highest percentages of recovery were obtained when we used 50 mM Tris-0.5% Tween 80 as the dispersing solution, dispersion for 15 min by stirring, and saturated NaCl as the flotation solution. The percentages of oocyst recovery from freshly spiked sandy loam, silty clay loam, and clay loam soils were ca. 12 to 18, 8, and 6%, respectively. The theoretical detection limits were ca. 1 to 2 oocysts g of soil-1 depending on the soil type. The percentages of recovery without dispersant (distilled H2O or phosphate-buffered saline) were less than 0.1%, which indicated that oocysts adhere to soil particles. The percentages of recovery decreased with storage time, although the addition of dispersant (Tris-Tween 80) before storage appeared to partially prevent adhesion. These data indicate that the NaCl flotation method is suitable for routine detection and enumeration of oocysts from feces, manures, soils, or soil-manure mixtures.

Use of a sentinel system for field measurements of Cryptosporidium parvum oocyst inactivation in soil and animal waste

A small-volume sentinel chamber was developed to assess the effects of environmental stresses on survival of sucrose-Percoll-purified Cryptosporidium parvum oocysts in soil and animal wastes. Chambers were tested for their ability to equilibrate with external chemical and moisture conditions. Sentinel oocysts were then exposed to stresses of the external environment that affected their viability (potential infectivity), as indicated by results of a dye permeability assay. Preliminary laboratory experiments indicated that temperatures between 35 and 50 degrees C and decreases in soil water potential (-0.003 to -3.20 MPa) increased oocyst inactivation rates. The effects of two common animal waste management practices on oocyst survival were investigated on three dairy farms in Delaware County, N.Y., within the New York City watershed: (i) piling wastes from dairy youngstock (including neonatal calves) and (ii) spreading wastes as a soil amendment on an agricultural field. Sentinel containers filled with air-dried and sieved (2-mm mesh) youngstock waste or field soil were wetted and inoculated with 2 million oocysts in an aqueous suspension and then placed in waste piles on two different farms and in soil within a cropped field on one farm. Controls consisted of purified oocysts in either phosphate-buffered saline or distilled water contained in sealed microcentrifuge tubes. Two microdata loggers recorded the ambient temperature at each field site. Sentinel experiments were conducted during the fall and winter (1996 to 1997) and winter (1998). Sentinel containers and controls were removed at 2- to 4-week intervals, and oocysts were extracted and tested by the dye permeability assay. The proportions of potentially infective oocysts exposed to the soil and waste pile material decreased more rapidly than their counterpart controls exposed to buffer or water, indicating that factors other than temperature affected oocyst inactivation in the waste piles and soil. The effect of soil freeze-thaw cycles was evident in the large proportion of empty sentinel oocysts. The potentially infective sentinel oocysts were reduced to <1% while the proportions in controls did not decrease below 50% potentially infective during the first field experiment. Microscopic observations of empty oocyst fragments indicated that abrasive effects of soil particles were a factor in oocyst inactivation. A similar pattern was observed in a second field experiment at the same site.

Influence of pretreatment and experimental conditions on electrophoretic mobility and hydrophobicity of Cryptosporidium parvum oocysts

Surface properties of Cryptosporidium parvum oocysts were investigated by using electrophoretic mobility and hydrophobicity measurements. Oocysts purified from calf feces by several sucrose flotation steps and deionized water (DI) washes (DIS method) had an electrophoretic mobility (neutral surface charge) near 0.0 m2 V-1 s-1 over a pH range of 2 to 10. The mean electrophoretic mobility of oocysts stored in DI containing a mixture of antibiotics had a lower standard deviation (sigma = 0.36) than that of oocysts stored in DI without antibiotics (sigma = 0.53); their electrophoretic mobility remained unchanged up to 121 days after collection. The electrophoretic mobility of oocysts purified on a cold Percoll-sucrose gradient after the feces was defatted with ethyl acetate (EAPS method) varied linearly with pH from 0.0 m2 V-1 s-1 at pH 2.4 to -3.2 x 10(-8) m2 V-1 s-1 at pH 10 (sigma = 0.52), thus displaying the negative surface charge at neutral pH observed by other researchers. The hydrophobicity of oocysts and two types of polystyrene beads was measured as a function of ionic strength by adhesion to polystyrene. Oocysts were purified by the DIS method. The ionic strength of the suspending solution was varied from 0 to 95 mmol liter-1. Two-week-old oocysts exhibited strong adhesion ( approximately 85%) at ionic strengths of 0 to 10 mmol liter-1 and moderate adhesion ( approximately 20%) at ionic strengths of 20 to 95 mmol liter-1. Two-month-old oocysts exhibited high adhesion ( approximately 60 to 80%) at all ionic strengths. These results show that adhesion properties governed by the electrophoretic mobility of purified C. parvum oocysts can be altered by the method of purification and that hydrophobicity can change as oocysts age.

Microbial Community Composition of Wadden Sea Sediments as Revealed by Fluorescence In Situ Hybridization

The microbial community composition of Wadden Sea sediments of the German North Sea coast was investigated by in situ hybridization with group-specific fluorescently labeled, rRNA-targeted oligonucleotides. A large fraction (up to 73%) of the DAPI (4',6-diamidino-2-phenylindole)-stained cells hybridized with the bacterial probes. Nearly 45% of the total cells could be further identified as belonging to known phyla. Members of the Cytophaga-Flavobacterium cluster were most abundant in all layers, followed by the sulfate-reducing bacteria.

Method detection limits of PCR and immunofluorescence assay for Cryptosporidium parvum in soil

We determined and compared the method detection limits (MDLalpha) of a PCR and an immunofluorescence assay (IFA) for detection of Cryptosporidium parvum oocysts in soils. Based on the MDLalpha and the quantitative nature and stability of the IFA, PCR analysis is not a useful screening step for soil studies of oocyst transport.

Sensitive and rapid detection of viable Giardia cysts and Cryptosporidium parvum oocysts in large-volume water samples with wound fiberglass cartridge filters and reverse transcription-PCR

We recently described a reverse transcription-PCR (RT-PCR) for detecting low numbers of viable Cryptosporidium parvum oocysts spiked into clarified environmental water concentrates. We have now modified the assay for direct analysis of primary sample concentrates with simultaneous detection of viable C. parvum oocysts, Giardia cysts, and a novel type of internal positive control (IPC). The IPC was designed to assess both efficiency of mRNA isolation and potential RT-PCR inhibition. Sensitivity testing showed that low numbers of organisms, in the range of a single viable cyst and oocyst, could be detected when spiked into 100-microliter packed pellet volumes of concentrates from creek and river water samples. The RT-PCR was compared with an immunofluorescence (IF) assay by analyzing 29 nonspiked environmental water samples. Sample volumes of 20 to 1,500 liters were concentrated with a wound fiberglass cartridge filter. Frequency of detection for viable Giardia cysts increased from 24% by IF microscopy to 69% by RT-PCR. Viable C. parvum oocysts were detected only once by RT-PCR (3%) in contrast to detection of viable Cryptosporidium spp. in four samples by IF microscopy (14%), suggesting that Cryptosporidium species other than C. parvum were present in the water. This combination of the large-volume sampling method with RT-PCR represents a significant advance in terms of protozoan pathogen monitoring and in the wider application of PCR technology to this field of microbiology.

Inactivation of Cryptosporidium parvum Oocysts by Ammonia

The survival of Cryptosporidium parvum oocysts in soil and water microhabitats may be affected by the environmental production and release of free ammonia. The objective of this study was to determine the effects of increasing free ammonia concentrations and times of exposure on oocyst viability. Wild-type oocysts were obtained from naturally infected calf feces by chemical (continuous-flow) centrifugation and sucrose gradients. Ammonia (NH 3 ) from a commercial solution was applied in concentrations ranging from 0.007 to 0.148 M. Exposure times ranged from 10 min to 24 h at a constant temperature of 24 ± 1°C. Viability of oocysts was determined with a dye permeability assay and an in vitro excystation assay (M. B. Jenkins, L. J. Anguish, D. D. Bowman, M. J. Walker, and W. C. Ghiorse, Appl. Environ. Microbiol. 63:3844–3850, 1997). Even the lowest concentration of ammonia decreased significantly the viability of oocysts after 24 h of exposure. Increasing concentrations of ammonia increased inactivation rates, which ranged from 0.014 to 0.066 h −1 . At the highest concentration of ammonia, a small fraction of viable oocysts still remained. Exposure to pH levels corresponding to those associated with the ammonia concentrations showed minimal effects of alkaline pH alone on oocyst viability. This study shows that environmentally relevant concentrations of free ammonia may significantly increase the inactivation of oocysts in ammonia-containing environments.

Assessment of a dye permeability assay for determination of inactivation rates of Cryptosporidium parvum oocysts

The ability to determine inactivation rates of Cryptosporidium parvum oocysts in environmental samples is critical for assessing the public health hazard of this gastrointestinal parasite in watersheds. We compared a dye permeability assay, which tests the differential uptake of the fluorochromes 4'-6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI) by the oocysts (A. T. Campbell, L. J. Robertson, and H. V. Smith, Appl. Environ. Microbiol. 58:3488-3493, 1992), with an in vitro excystation assay, which tests their ability to excyst and, thus, their metabolic potential and potential for infectivity (J.B. Rose, H. Darbin, and C.P. Gerba, Water Sci. Technol. 20:271-276, 1988). Formaldehyde-fixed (killed) oocysts and untreated oocysts were permeabilized with sodium hypochlorite and subjected to both assays. The results of the dye permeability assays were the same, while the excystation assay showed that no excystation occurred in formaldehyde-fixed oocysts. This confirmed that oocyst wall permeability, rather than metabolic activity potential, was the basis of the dye permeability viability assessment. A previously developed protocol (L. J. Anguish and W. C. Ghiorse, Appl. Environ. Microbiol. 63:724-733, 1997) for determining viability of oocysts in soil and sediment was used to examine further the use of oocyst permeability status as an indicator of oocyst viability in fecal material stored at 4 degrees C and in water at various temperatures. Most of the oocysts in fresh calf feces were found to be impermeable to the fluorochromes. They were also capable of excystation, as indicated by the in vitro excystation assay, and were infective, as indicated by a standard mouse infectivity assay. The dye permeability assay further showed that an increase in the intermediate population of oocysts permeable to DAPI but not to PI occurred over time. There was also a steady population of oocysts permeable to both dyes. Further experiments with purified oocysts suspended in distilled water showed that the shift in oocyst populations from impermeable to partially permeable to fully permeable was accelerated at temperatures above 4 degrees C. This sequence of oocyst permeability changes was taken as an indicator of the oocyst inactivation pathway. Using the dye permeability results, inactivation rates of oocysts in two fecal pools stored in the dark at 4 degrees C for 410 and 259 days were estimated to be 0.0040 and 0.0056 oocyst day-1, respectively. The excystation assay gave similar inactivation rates of 0.0046 and 0.0079 oocyst day-1. These results demonstrate the utility of the dye permeability assay as an indicator of potential viability and infectivity of oocysts, especially when combined with improved microscopic methods for detection of oocysts in soil, turbid water, and sediments.