Composition and Conformation of Cryptosporidium parvum Oocyst Wall Surface Macromolecules and Their Effect on Adhesion Kinetics of Oocysts on Quartz Surface

Comparison of in vitro growth characteristics of Cryptosporidium hominis (IdA15G1) and Cryptosporidium parvum (Iowa-IIaA17G2R1 and IIaA18G3R1)

Cryptosporidium is a major cause of diarrhoeal disease and mortality in young children in resource-poor countries, for which no vaccines or adequate therapeutic options are available. Infection in humans is primarily caused by two species: C. hominis and C. parvum. Despite C. hominis being the dominant species infecting humans in most countries, very little is known about its growth characteristics and life cycle in vitro, given that the majority of our knowledge of the in vitro development of Cryptosporidium has been based on C. parvum. In the present study, the growth and development of two C. parvum isolates (subtypes Iowa-IIaA17G2R1 and IIaA18G3R1) and one C. hominis isolate (subtype IdA15G1) in HCT-8 cells were examined and compared at 24 h and 48 h using morphological data acquired with scanning electron microscopy. Our data indicated no significant differences in the proportion of meronts or merozoites between species or subtypes at either time-point. Sexual development was observed at the 48-h time-point across both species through observations of both microgamonts and macrogamonts, with a higher frequency of macrogamont observations in C. hominis (IdA15G1) cultures at 48-h post-infection compared to both C. parvum subtypes. This corresponded to differences in the proportion of trophozoites observed at the same time point. No differences in proportion of microgamonts were observed between the three subtypes, which were rarely observed across all cultures. In summary, our data indicate that asexual development of C. hominis is similar to that of C. parvum, while sexual development is accelerated in C. hominis. This study provides new insights into differences in the in vitro growth characteristics of C. hominis when compared to C. parvum, which will facilitate our understanding of the sexual development of both species.

Past and future trends of Cryptosporidium in vitro research

Cryptosporidium is a genus of single celled parasites capable of infecting a wide range of animals including humans. Cryptosporidium species are members of the phylum apicomplexa, which includes well-known genera such as Plasmodium and Toxoplasma. Cryptosporidium parasites cause a severe gastro-intestinal disease known as cryptosporidiosis. They are one of the most common causes of childhood diarrhoea worldwide, and infection can have prolonged detrimental effects on the development of children, but also can be life threatening to HIV/AIDS patients and transplant recipients. A variety of hosts can act as reservoirs, and Cryptosporidium can persist in the environment for prolonged times as oocysts. While there has been substantial interest in these parasites, there is very little progress in terms of treatment development and understanding the majority of the life cycle of this unusual organism. In this review, we will provide an overview on the existing knowledge of the biology of the parasite and the current progress in developing in vitro cultivation systems. We will then describe a synopsis of current and next generation approaches that could spearhead further research in combating the parasite.

An easy 'one tube' method to estimate viability of Cryptosporidium oocysts using real-time qPCR

Viability estimation of the highly resistant oocysts of Cryptosporidium remains a key issue for the monitoring and control of this pathogen. We present here a simple 'one tube' quantitative PCR (qPCR) protocol for viability estimation using a DNA extraction protocol which preferentially solubilizes excysted sporozoites rather than oocysts. Parasite DNA released from excysted sporozoites was quantified by real-time qPCR using a ribosomal DNA marker. The qPCR signal was directly proportional to the number of oocysts excysted, and a power-law relationship was noted between oocyst age and the proportion excysting. Unexcysted oocysts released negligible amounts of DNA making the method suitable for estimating viability of as few as 10 oocysts.

Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces

Mechanisms of Escherichia coli attachment on biofilms grown on PVC coupons were investigated. Biofilms were grown in CDC reactors using groundwater as feed solution over a period up to 27 weeks. Biofilm physical structure was characterized at the micro- and meso-scales using Scanning Electron Microscopy (SEM) and Optical Coherence Tomography (OCT), respectively. Microbial community diversity was analyzed with Terminal Restricted Fragment Length Polymorphism (T-RFLP). Both physical structure and microbial community diversity of the biofilms were shown to be changing from 2 weeks to 14 weeks, and became relatively stable after 16 weeks. A parallel plate flow chamber coupled with an inverted fluorescent microscope was also used to monitor the attachment of fluorescent microspheres and E. coli on clean PVC surfaces and biofilms grown on PVC surfaces for different ages. Two mechanisms of E. coli attachment were identified. The adhesion rate coefficients (kd) of E. coli on nascent PVC surfaces and 2-week biofilms increased with ionic strength. However, after biofilms grew for 8 weeks, the adhesion was found to be independent of solution chemistry. Instead, a positive correlation between kd and biofilm roughness as determined by OCT was obtained, indicating that the physical structure of biofilms could play an important role in facilitating the adhesion of E. coli cells.

Role of collector alternating charged patches on transport of Cryptosporidium parvum oocysts in a patchwise charged heterogeneous micromodel

The role of collector surface charge heterogeneity on transport of Cryptosporidium parvum oocyst and carboxylate microsphere in 2-dimensional micromodels was studied. The cylindrical silica collectors within the micromodels were coated with 0, 10, 20, 50, and 100% Fe(2)O(3) patches. The experimental values of average removal efficiencies (η) of the Fe(2)O(3) patches and on the entire collectors were determined. In the presence of significant (>3500 kT) Derjaguin-Landau-Verwey-Overbeek (DLVO) energy barrier between the microspheres and the silica collectors at pH 5.8 and 8.1, η determined for Fe(2)O(3) patches on the heterogeneous collectors were significantly less (p < 0.05, t test) than those obtained for collectors coated entirely with Fe(2)O(3). However, η calculated for Fe(2)O(3) patches for microspheres at pH 4.4 and for oocysts at pH 5.8 and 8.1, where the DLVO energy barrier was relatively small (ca. 200-360 kT), were significantly greater (p < 0.05, t test) than those for the collectors coated entirely with Fe(2)O(3). The dependence of η for Fe(2)O(3) patches on the DLVO energy barrier indicated the importance of periodic favorable and unfavorable electrostatic interactions between colloids and collectors with alternating Fe(2)O(3) and silica patches. Differences between experimentally determined overall η for charged heterogeneous collectors and those predicted by a patchwise geochemical heterogeneous model were observed. These differences can be explained by the model's lack of consideration for the spatial distribution of charge heterogeneity on the collector surface.

Targeting Cryptosporidium parvum capture

Polymer microarrays offer a high-throughput approach to the screening and assessment of a large number of polymeric materials. Here, we report the first study of protozoan-polymer interactions using a microarray approach. Specifically, from screening hundreds of synthetic polymers, we identified materials that either trap the waterborne protozoan parasite, Cryptosporidium parvum, or prevent its adhesion, both of which have major practical applications. Comparison of array results revealed differences in the adhesion characteristics of viable and non-viable C. parvum oocysts. Material properties, including polymer composition, wettability and surface chemistry, allowed correlation of binding and identification of structure function relationships. Understanding C. parvum binding interactions could assist in improved water treatment processes and the identified polymers could find applications in sensor and filter materials.

Analysis of Giardia lamblia interactions with polymer surfaces using a microarray approach

The interaction of the waterborne protozoan parasite, Giardia lamblia, with polymeric materials was investigated by microarray screening of 652 polymers. Polymers were identified which either bound G. lamblia cysts or prevented their binding. Correlation of material properties such as wettability and surface roughness with cyst attachment revealed no influence of these factors upon Giardia adhesion. However, the study of polymer composition allowed the correlation of binding and generation of polymer structure function relationships; glycol and aromatic functionalities appeared to prevent adhesion, whereas secondary amine groups promoted adhesion, in agreement with previous literature. A significant reduction in attachment was observed following both cyst treatments with proteinase K and performing experiments at extremes of pH (2 and 12). It is suggested that proteinase K removes the proteins needed for specific surface interactions, whereas extremes of pH influence either protonation of the polymer or the surface charge of the cysts. The mechanism by which the protozoa attach to polymeric surfaces is proposed to be through ion-pair interactions. Improved understanding of G. lamblia surface interactions could assist in predicting transport and fate behavior in the environment and contribute to better design of water treatment processes, while the polymers identified in this work could find use in sensor applications and membrane filtration.

Transport of Cryptosporidium parvum oocysts in a silicon micromodel

Effective removal of Cryptosporidium parvum oocysts by granular filtration requires the knowledge of oocyst transport and deposition mechanisms, which can be obtained based on real time microscopic observation of oocyst transport in porous media. Attachment of oocysts to silica surface in a radial stagnation point flow cell and in a micromodel, which has 2-dimensional (2-D) microscopic pore structures consisting of an array of cylindrical collectors, was studied and compared. Real time transport of oocysts in the micromodel was recorded to determine the attached oocyst distributions in transversal and longitudinal directions. In the micromodel, oocysts attached to the forward portion of clean collectors, where the flow velocity was lowest. After initial attachment, oocysts attached onto already attached oocysts. As a result, the collectors ripened and the region available for flow was reduced. Results of attachment and detachment experiments suggest that surface charge heterogeneity allowed for oocyst attachment. In addition to experiments, Lattice-Boltzmann simulations helped understanding the slightly nonuniform flow field and explained differences in the removal efficiency in the transversal direction. However, the hydrodynamic modeling could not explain differences in attachment in the longitudinal direction.

The influence of biofilm structure and total interaction energy on Escherichia coli retention by Pseudomonas aeruginosa biofilm

The retention of a surrogate pathogenic bacterium, Escherichia coli(T) , in Pseudomonas aeruginosa biofilms (with various EPS excreting capacities) was investigated using a laboratory flow cell system. The structural characteristics of the biofilm, as well as the quantity of E. coli(T) retained in the biofilm, were assessed using confocal laser scanning microscopy coupled with image analysis. In addition, the total interaction energy between E. coli(T) and the P. aeruginosa biofilm was computed with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which provided an additional context to explain the pathogen interaction in aquatic biofilms. The correlations between the quantity of detained E. coli(T) cells and the structural characteristics of the biofilm were analysed and the results indicated that the heterogeneity of the biofilm could create a quiescent zone leading to temporary retention of E. coli(T) within the biofilm. Overall, this study provided insights toward understanding the retention of pathogenic bacteria in environmental biofilms.

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.