Cryptosporidium attachment to functionalized surfaces

Cryptosporidium is a protozoan parasite that causes severe gastrointestinal disease worldwide. Originally, Cryptosporidium was recognized as an opportunistic pathogen in immunocompromised patients but can also be found in immunocompetent hosts – typically causing asymptomatic or otherwise self-limited infections. The Cryptosporidium life cycle begins with the ingestion of food or water contaminated with oocysts, followed by an excystation process in the small intestine, infection of the intestinal epithelial cells, and lastly the production of oocysts that are then excreted and released into the environment. Despite intervention via water treatments and regulatory compliance by water suppliers, sporadic outbreaks of infections have occurred due to the oocysts' small size (4-8 ?m) and chlorine resistance.Previously, the transport of C. parvum oocysts in aquatic environments was found to be influenced by interactions with naturally occurring environmental biofilms. In this body of work, polydopamine (PD) – which exhibits similar chemical moieties to that of naturally occurring environmental biofilms and serves as an excellent coating material due to its strong adhesion properties – was functionalized onto glass substrates to explore its capacity for C. parvum oocyst attachment under varying water chemistries and induced shear forces (Chapter 2). An unexpected discovery was made while observing the attachment of C. parvum oocysts to PD surfaces: the elicitation of excystation. PD surfaces decorated with glycosaminoglycans (GAGs) were shown to provide an additional stimulus for excystation – thus this study presents a potential non-cellular trigger for excystation that can easily be built into PD surfaces (Chapter 3). Our results suggest that the glycocalyx or some surface-expressed receptor plays a key role in the induction of excystation, with GAGs serving as a mediating effect.A review of the current state of knowledge on modelling Cryptosporidium oocyst – surface interactions was conducted where we examine the deviation of experimental results from theoretical predictions by the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory classical colloid filtration theory (CFT) (Chapter 4). For computational expediency, previous studies have applied DLVO modeling to C. parvum oocyst adhesion and transport using the limiting cases of constant electrostatic potential (CP) or constant charge (CC). However, these assumptions fail to accurately consider the charge regulation (CR) effect. This phenomenon occurs as an ionizable surface approaches another surface in an aqueous system there is an overlap of the surface's electric double layers (EDL) resulting in the variation in the electrostatic potential, charge, and pH that occurs as a function of separation distance. Thus, the CR – zeta potential (?) approach was applied to PD aggregates and C. parvum oocysts by analyzing zeta potential data obtained at multiple pH and ionic strength values in order to obtain the equilibrium constants (K) and site densities (N) of the dominant surface functional groups that best represent the electrostatic properties of the surface (Chapter 5). These resultant values were then used to demonstrate the variations in surface charge, electrostatic potential, and pH that can occur as the charge-regulated surfaces interact.Elucidating novel factors involved in attachment and excystation of oocysts would contribute toward a myriad of potential applications, such as inactivation or disinfection strategies relevant for water treatment, the development of therapies against Cryptosporidium infection, and the design of collector surfaces for oocyst detection and removal from aquatic systems.