Quantification of Cryptosporidium parvum in natural soil matrices and soil solutions using qPCR

Nanoparticle Lysis of Cryptosporidium Oocysts

The extraction of DNA from Cryptosporidium oocysts is challenging due to the robust oocyst wall. Nanoparticles have been applied to disinfect Cryptosporidium oocysts; here, we demonstrate the utilisation of nanoparticles to disrupt the oocyst wall to enable sporozoite lysis and detection via PCR. Both silver and zinc oxide nanoparticles are investigated under different conditions and compared to existing techniques. Zinc oxide nanoparticles are shown to be as effective as freeze-thaw methods, suggesting that a nanoparticle lysis approach offers a viable alternative to existing methods.

Detection, fate and transport of the biohazardous agent Toxoplasma gondii in soil water systems: Influence of soil physicochemical properties, water chemistry and surfactant

A series of laboratory experiments were conducted to study the fate and transport of Toxoplasma gondii oocysts in soils as a function of soil physicochemical properties and soil water chemistry properties. Soil columns were homogeneously packed with loamy sand soils (Lewiston and Greenson series) and sandy loam soils (Sparta and Gilford series), and subject to hydrologic conditions characterized by the absence and presence of an anionic surfactant-Aerosol 22 in the artificial rainfall. Quantitative polymerase chain reaction (qPCR) was utilized for the detection and enumeration of oocysts in soil leachates to evaluate their breakthrough and in soil matrices to examine their spatial distribution. Differences in the rate and extent of transport of oocysts were observed as a function of physical and chemical parameters tested. The breakthrough of oocysts was observed for all the soils irrespective of the presence of surfactant. However, in the absence of surfactant, the predominant fate of oocysts in soils subject to simulated rainfall was their retention in the soil profile. The presence of surfactant induced a change in the fate of oocysts in these soils exposed to rainfall simulation as the predominant fate of oocysts was found to be in the soil leachates.

What on earth? The impact of digestates and composts from farm effluent management on fluxes of foodborne pathogens in agricultural lands

The recycling of biomass is the cornerstone of sustainable development in the bioeconomy. In this context, digestates and composts from processed agricultural residues and biomasses are returned to the soil. Whether or not the presence of pathogenic microorganisms in these processed biomasses is a threat to the sustainability of the current on-farm practices is still the subject of debate. In this review, we describe the microbial pathogens that may be present in digestates and composts. We then provide an overview of the current European regulation designed to mitigate health hazards linked to the use of organic fertilisers and soil improvers produced from farm biomasses and residues. Finally, we discuss the many factors that underlie the fate of microbial pathogens in the field. We argue that incorporating land characteristics in the management of safety issues connected with the spreading of organic fertilisers and soil improvers can improve the sustainability of biomass recycling.

A Simple Alcohol-based Method of Oocyst Inactivation for Use in the Development of Detection Assays for Cryptosporidium

Cryptosporidium spp. are obligate, intracellular parasites that cause life-threatening diarrhea among children and immunocompromised adults. Transmission occurs by the fecal-oral route following ingestion of thick-walled oocysts that can contaminate, persist, and resist disinfection in water and food. Sodium hypochlorite, peroxides, ozone, formaldehyde, and ammonia are suitable disinfectants against Cryptosporidium oocysts. Effective concentrations of these chemicals can be toxic and not practical for downstream research use of non-viable oocysts. Oocyst inactivation approaches such as UV light, heat, and treatments with ethanol or methanol are generally more accessible for routine lab use, yet their applicability in Cryptosporidium assay development is limited. The aims of this study were to evaluate methods of inactivation of Cryptosporidium oocysts that can be readily applied in the laboratory and test the utility of whole inactive oocysts in quantitative PCR (qPCR). Experiments were performed on C. parvum oocysts subjected to heat (75 °C/10 min) or treated with increasing concentrations of ethanol and methanol over time. Viability assays based on propidium iodide (PI) staining, in vitro excystation, and infection of the Hct-8 cell line were used to evaluate the efficacies of the treatments. Excystation of sporozoites was not impaired with 24 h exposures of oocysts to 50% ethanol or methanol, even though significant PI incorporation was observed. Concentrations of ≥70% of these chemicals were required to completely inhibit excystation and infection of Hct-8 cells in vitro. Inactivated oocysts stored for up to 30 days at 4 °C retained cyst wall integrity and antigenicity as observed by light microscopy and immunofluorescence. Moreover, non-viable oocysts applied directly in qPCR assays of the COWP gene were useful reference reagents for the identification and quantification of Cryptosporidium in spiked water samples. In summary, we have established a practical approach to inactivate C. parvum oocysts in the laboratory that is suitable for the development of detection or diagnostic assays targeting the parasite.

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Disinfectant-based inactivation of oocysts is not feasible for assay development.

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Inactivation methods that retain antigen and nucleic acid integrity are limited.

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Alcohol-inactivated oocysts are suitable as reference reagents in qPCR.

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We present a method to effectively inactivate oocysts and retain assayable properties.

Assessment of differences between DNA content of cell-cultured and freely suspended oocysts of Cryptosporidium parvum and their suitability as DNA standards in qPCR

BACKGROUND

Although more modern methods are available, quantitative PCR (qPCR) is reproducible, sensitive and specific with instruments and expertise readily available in many laboratories. As such, the use of qPCR in Cryptosporidium research is well established and still widely used by researchers globally. This method depends upon the generation of standards at different concentrations to generate standard curves subsequently used for the quantification of DNA.

METHODS

We assessed four types of DNA template used to generate standard curves in drug screening studies involving Cryptosporidium spp.: (i) serially diluted Cryptosporidium parvum oocysts (106-1); (ii) diluted template DNA from pure oocysts (×10-×106 dilution of 106 oocyst DNA template); (iii) oocysts incubated in human ileocecal adenocarcinoma (HCT-8) cells (105-1 and 5 × 104-50); and (iv) diluted DNA template (5 × 104) from cell culture incubated parasites (×10-×1000).

RESULTS

Serial dilutions of both cell culture and pure oocyst suspension DNA template yielded better linearity than cell culture derived standards, with dilutions of 106 oocysts exhibiting similar quantification cycle (Cq) values to those obtained from DNA template dilutions of 106 oocysts. In contrast, cell culture incubated oocysts demonstrated significantly higher DNA content than equivalent freely suspended oocysts and diluted DNA template from both cell culture derived and freely suspended oocysts across numerous concentrations.

CONCLUSIONS

For many studies involving Cryptosporidium, only relative DNA content is required and as such, the superior linearity afforded by freely suspended oocysts and diluted DNA template (from either cell culture derived standards or freely suspended oocysts) will allow for more accurate relative quantification in each assay. Parasite division in the cell culture standards likely explains the higher DNA content found. These standards, therefore, have the potential to more accurately reflect DNA content in cell culture assays, and despite more modern methods available for absolute quantification, i.e. droplet digital PCR (ddPCR), the ubiquity of qPCR for the foreseeable future encourages further investigation into the reduced linearity observed in these standards such as varying oocyst seeding density, non-linear growth rates and assay efficiency.

Real-time nucleic acid sequence-based amplification (NASBA) assay targeting MIC1 for detection of Cryptosporidium parvum and Cryptosporidium hominis oocysts

Both Cryptosporidium parvum and Cryptosporidium hominis are often associated with cryptosporidiosis in humans, but whereas humans are the main host for C. hominis, C. parvum is zoonotic and able to infect a variety of species. The oocyst transmission stages of both species of parasites are morphologically identical and molecular techniques, usually polymerase chain reaction (PCR), are required to distinguish between oocysts detected by standard methods in environmental samples, such as water. In this study, we developed two primer sets for real-time nucleic acid sequence-based amplification (NASBA), targeting the MIC1 transcript in C. parvum (CpMIC1) and C. hominis (ChMIC1). Using these primer sets, we were not only able to detect low numbers of C. parvum and C. hominis oocysts (down to 5 oocysts in 10 μl, and down to 1 oocyst using diluted RNA samples), but also distinguish between them. One of the primer sets targeted an exon only occurring in CpMIC1, thereby providing a tool for distinguishing C. parvum from other Cryptosporidium species. Although mRNA has been suggested as a tool for assessing viability of Cryptosporidium oocysts, as it is short-lived and may have high transcription, this NASBA assay detected MIC1 mRNA in inactivated oocysts. RNA within the oocysts seems to be protected from degradation, even when the oocysts have been killed by heating or freeze-thawing. Thus, our approach detects both viable and non-viable oocysts, and RNA does not seem to be a suitable marker for assessing oocyst viability.

Quantitative microbial risk assessment of Cryptosporidium and Giardia in well water from a native community of Mexico

Cryptosporidium and Giardia are gastrointestinal disease-causing organisms transmitted by the fecal-oral route, zoonotic and prevalent in all socioeconomic segments with greater emphasis in rural communities. The goal of this study was to assess the risk of cryptosporidiosis and giardiasis of Potam dwellers consuming drinking water from communal well water. To achieve the goal, quantitative microbial risk assessment (QMRA) was carried out as follows: (a) identification of Cryptosporidium oocysts and Giardia cysts in well water samples by information collection rule method, (b) assessment of exposure to healthy Potam residents, (c) dose-response modelling, and (d) risk characterization using an exponential model. All well water samples tested were positive for Cryptosporidium and Giardia. The QMRA results indicate a mean of annual risks of 99:100 (0.99) for cryptosporidiosis and 1:1 (1.0) for giardiasis. The outcome of the present study may drive decision-makers to establish an educational and treatment program to reduce the incidence of parasite-borne intestinal infection in the Potam community, and to conduct risk analysis programs in other similar rural communities in Mexico.

Recovery of Cryptosporidium and Giardia organisms from surface water by counter-flow refining microfiltration

As waterborne parasitic cryptosporidiosis and giardiasis outbreaks continue globally, monitoring of Cryptosporidium parvum and Giardia lamblia in surface water continues to be challenging. Lack of non-clogging and high-efficiency methods for recovery of C. parvum oocysts and G. lamblia cysts in environmental water strongly limits the sensitivity of detection methods for these protozoan organisms. In this work, the Counter-Flow Micro-Refinery (CFMR) system was developed by employing the novel counter-flow microfiltration principle to enrich (oo)cysts for subsequent analytical purposes. The CFMR system was constructed with multiple counter-flow concentration units that were arranged into two refining levels. By use of different numbers of units, the CFMR offered an adjustable concentration ratio allowing the concentration of 10 L and 100 L to hundreds of mL with no recirculation processing. With spiked samples, recovery of 81.3% oocysts and 86.2% cysts at a variance of < 7% was achieved for concentrations as low as 0.5-100 organisms L(-1). The recovery efficiency showed consistent for a wide range of water turbidities as well as different sample volumes. No significant clogging has been observed in the experiments. Moreover, the refining filter was able to enrich and separate oocysts and cysts in water, simultaneously. This work verifies a feasible solution for recovering C. parvum oocysts and G. lamblia cysts in large-volume surface waters. The refining system has potential to be a high-efficiency monitoring tool when combined with proper analytical detection methods.