Mechanisms controlling the adhesion of Cryptosporidium parvum oocysts to solid surfaces

A radial stagnation point flow (RSPF) system was used to investigate the influence of Cryptosporidium parvum surface macromolecules on the deposition kinetics of oocysts onto an ultra-pure quartz surface. Optical microscopy coupled with an image-capturing device enabled real time observation of oocyst deposition behavior onto the quartz surface in solutions containing either monovalent (KCl) or divalent (CaCl2) salts. Results showed significantly low oocyst deposition rates and corresponding attachment efficiencies in the presence of monovalent salt, even at high ionic strengths where the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability predicts the absence of an electrostatic energy barrier. In the presence of divalent salt, oocyst deposition rates increased continuously as divalent salt concentration increased. Nonetheless, the attachment efficiency was still far from unity in the presence of divalent ions, even at high ionic strengths. An "electrosteric" repulsion between viable Cryptosporidium oocyst and the quartz substrate, attributed to macromolecules on the oocyst surface, is surmised to cause this low deposition rate. Treatment of the oocysts with either heat or formalin resulted in increased deposition rates, most likely due to the alteration of the structure of these surface glycoproteins and subsequent reduction of the steric repulsion with the quartz substrate.; To further investigate the role of surface macromolecules, the oocysts were treated with a protease enzyme, Proteinase K. Increased attachment efficiencies were seen over the entire range of ionic strengths investigated after treatment with Proteinase K, despite the oocysts having a more negative zeta potential. It is concluded that after the removal of surface macromolecules, the oocysts no longer experienced an "electrosteric" force, and their deposition kinetics could be described more accurately by classical DLVO theory.; Granular filtration of natural pathogens, such as Cryptosporidium oocysts, is one of the primary barriers for their removal during drinking water treatment. The removal mechanisms in porous media of model colloidal particles of similar size to protozoa such as Cryptosporidium parvum oocysts were investigated by use of a flow-cell. While the RSPF system was able to enumerate oocyst deposition in the primary minima, direct visualization of colloidal particle deposition showed that deposition in the secondary minimum was an important removal mechanism during physicochemical filtration.