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

Evaluation of molecular-based methods for the detection and quantification of Cryptosporidium spp. in wastewater

Cryptosporidium poses significant public health risks as a cause of waterborne disease worldwide. Clinical surveillance of cryptosporidiosis is largely underreported due to the asymptomatic and mildly symptomatic infections, clinical misdiagnoses, and barriers to access testing. Wastewater surveillance overcomes these limitations and could serve as an effective tool for identifying cryptosporidiosis at the population level. Despite its potential, the lack of standardized wastewater surveillance methods for Cryptosporidium spp. challenges implementation design and the comparability between studies. Thus, this study compared and contrasted Cryptosporidium wastewater surveillance methods for concentrating wastewater oocysts, extracting oocyst DNA, and detecting Cryptosporidium genetic markers. The evaluated concentration methods included electronegative membrane filtration, Envirocheck HV capsule filtration, centrifugation, and Nanotrap Microbiome Particles, with and without additional immunomagnetic separation purification (except for the Nanotrap Microbiome Particles). Oocyst DNA extraction by either the DNeasy Powersoil Pro kit and the QIAamp DNA Mini kit were evaluated and the impact of bead beating and freeze-thaw pretreatments on DNA recoveries was assessed. Genetic detection via qPCR assays targeting either the Cryptosporidium 18S rRNA gene or the Cryptosporidium oocyst wall protein gene were tested. Oocyst recovery percentages were highest for centrifugation (39-77 %), followed by the Nanotrap Microbiome Particles (24 %), electronegative filtration with a PBST elution (22 %), and Envirocheck HV capsule filtration (13 %). Immunomagnetic separation purification was found to be unsuitable due to interference from the wastewater matrix. Bead-beating pretreatment enhanced DNA recoveries from both the DNeasy Powersoil Pro kit (314 gc/μL DNA) and the QIAamp DNA Mini kit (238 gc/μL DNA). In contrast, freeze-thaw pretreatment reduced DNA recoveries to under 92 gc/μL DNA, likely through DNA degradation. Finally, while both qPCR assays were specific to Cryptosporidium spp., the 18S rRNA assay had a 5-fold lower detection limit and could detect a wider range of Cryptosporidium spp. than the Cryptosporidium oocyst wall protein assay.

Interaction forces drive the environmental transmission of pathogenic protozoa

The protozoan parasites Giardia duodenalis, Cryptosporidium spp., and Toxoplasma gondii are pathogens that are resistant to a number of environmental factors and pose significant risks to public health worldwide. Their environmental transmission is closely governed by the physicochemical properties of their cysts (Giardia) and oocysts (Cryptosporidium and Toxoplasma), allowing their transport, retention, and survival for months in water, soil, vegetables, and mollusks, which are the main reservoirs for human infection. Importantly, the cyst/oocyst wall plays a key role in that regard by exhibiting a complex polymeric coverage that determines the charge and hydrophobic characteristics of parasites' surfaces. Interaction forces between parasites and other environmental particles may be, in a first approximation, evaluated following the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. However, due to the molecular topography and nano- to microstructure of the cyst/oocyst surface, non-DVLO hydrophobic forces together with additional steric attractive and/or repulsive forces may play a pivotal role in controlling the parasite behavior when the organism is subjected to various external conditions. Here, we review several parameters that enhance or hinder the adhesion of parasites to other particles and surfaces and address the role of fast-emerging techniques for mapping the cyst/oocyst surface, e.g., by measuring its topology and the generated interaction forces at the nano- to microscale. We discuss why characterizing these interactions could be a crucial step for managing the environmental matrices at risk of microbial pollution.

Cryptosporidium oocyst detection in water samples: floatation technique enhanced with immunofluorescence is as effective as immunomagnetic separation method

Cryptosporidium can cause gastrointestinal diseases worldwide, consequently posing public health problems and economic burden. Effective techniques for detecting contaminated oocysts in water are important to prevent and control the contamination. Immunomagnetic separation (IMS) method has been widely employed recently due to its efficiency, but, it is costly. Sucrose floatation technique is generally used for separating organisms by using their different specific gravity. It is effective and cheap but time consuming as well as requiring highly skilled personnel. Water turbidity and parasite load in water sample are additional factors affecting to the recovery rate of those 2 methods. We compared the efficiency of IMS and sucrose floatation methods to recover the spiked Cryptosporidium oocysts in various turbidity water samples. Cryptosporidium oocysts concentration at 1, 10(1), 10(2), and 10(3) per 10 microl were spiked into 3 sets of 10 ml-water turbidity (5, 50, and 500 NTU). The recovery rate of the 2 methods was not different. Oocyst load at the concentration < 10(2) per 10 ml yielded unreliable results. Water turbidity at 500 NTU decreased the recovery rate of both techniques. The combination of sucrose floatation and immunofluorescense assay techniques (SF-FA) showed higher recovery rate than IMS and immunofluorescense assay (IMS-FA). We used this SF-FA to detect Cryptosporidium and Giardia from the river water samples and found 9 and 19 out of 30 (30% and 63.3%) positive, respectively. Our results favored sucrose floatation technique enhanced with immunofluorescense assay for detecting contaminated protozoa in water samples in general laboratories and in the real practical setting.

Evaluation of two DNA template preparation methods for post-immunomagnetic separation detection of Cryptosporidium parvum in foods and beverages by PCR

Cryptosporidium parvum oocysts were recovered by immunomagnetic separation from six artificially contaminated foods. Two DNA isolation methods were subsequently evaluated by PCR. The FTA Concentrator-PS filter provided rapid and reproducible detection, although variability increased at lower inoculum levels (88% and 15% detection in high- and low-inoculum-level samples, respectively). Total DNA extraction generated consistent results at all oocyst levels but resulted in longer analysis time (100% and 59% detection in high- and low-inoculum-level samples, respectively). Also reflected in this study was that the matrix played an important role in the ability to recover oocysts, as sample turbidity, pH, and PCR inhibitors all influenced detection.

Quantitative and qualitative comparisons of Cryptosporidium faecal purification procedures for the isolation of oocysts suitable for proteomic analysis

With the recent publication of the Cryptosporidium genome, investigation of the proteins expressed by Cryptosporidium parvum will provide complementary information on the biology of this complex organism. Proteomic studies on this apicomplexan parasite have been hampered due to the inability to culture or isolate high numbers required for 2D gel analysis. Neonatal calves are a common source of Cryptosporidium oocysts and we report on the development of a sucrose-Percoll purification procedure which produced the high yield and purity (free from faecal and bacterial contaminants) that is required for successful proteomic studies from neonatal calves. We report on the development of quantitative and qualitative flow cytometric methods which were confirmed by epifluorescence microscopy. A comparison of five common purification procedures was carried out to determine the efficiency of the sucrose-Percoll gradient. 2D-PAGE results strongly support the sucrose-Percoll procedure as the most suitable method for applications like proteomics which require the recovery of high numbers of isolated oocysts with minimal faecal and bacterial contaminants.

Comparison of two target genes for detection and genotyping of Giardia lamblia in human feces by PCR and PCR-restriction fragment length polymorphism

A PCR assay targeting the tpi gene was developed to detect and to genotype Giardia lamblia in human feces. Our assay was specific and discriminated between G. lamblia assemblages A and B. G. lamblia cysts isolated from human feces were also analyzed with two previously described PCR-restriction fragment length polymorphism (RFLP) assays, which are based on the detection of tpi or gdh genes. These RFLP analyses distinguished groups I and II within assemblage A or groups III and IV within assemblage B. Among 26 fecal samples from patients with sporadic giardiasis diagnosed by hospital laboratories, the tpi gene was amplified from 25 (96%) with our PCR assay, whereas only 21 (81%) samples were positive when the gdh gene was targeted. Of the 25 positive samples, nine (36%) contained assemblage A and 16 (64%) contained assemblage B. Thus, RFLP analysis classified eight samples (32%) in assemblage A group II, eight (32%) in assemblage B group III, and five (20%) in assemblage B group IV. The group could not be specified for four samples. The tpi and gdh genes of G. lamblia assemblage B were amplified from 14 (93%) of 15 samples collected only from French soldiers coming back from the Ivory Coast. All of these contained assemblage B group III. The PCR method developed is sensitive, simple, and specific and shows that the tpi gene is well adapted for G. lamblia genotyping.

Development of a sensitive detection system for Cryptosporidium in environmental samples

The identification of Cryptosporidium species and genotypes is necessary to determine sources of infection in outbreaks and the risk factors associated with their transmission. Few studies have applied isolation methods to field samples because of difficulties with detection of oocysts in environmental samples, particularly in soil and manure. The objective of this study was to develop an easy to use method which can be applied to field samples to rapidly detect the presence of Cryptosporidium parasites and identify their species. The assay included an oocyst recovery method combined with spin column DNA extraction, followed by PCR-hybridization for detection and a real-time PCR-melting curve analysis for species assignment. An internal positive control (IPC) was developed to determine the presence of PCR inhibitory substances. Two oocyst recovery methods, sodium chloride and sucrose flotation techniques were compared. Two commercial DNA extraction kits were performed using feces, soil and water samples each inoculated with different concentration of Cryptosporidium oocysts. Subsequently, methods were used to test field samples. The sucrose flotation method provided the greatest analytical sensitivity detecting as few as 10 oocysts. The PCR-hybridization detection limit was 10 oocysts for feces and soil, and less than 10 oocysts for water samples. IPC was positive for all inoculated and field samples indicating 0% PCR inhibition. Cryptosporidium species DNA samples were detected with the real-time PCR and were differentiated by the melting curve analysis. The results of this study demonstrate the potential of the assay system for rapid detection of Cryptosporidium parasites in environmental samples.