ATR-FTIR Studies of Cryptosporidium Parvum Öocysts at Mineral Surfaces.

Cryptosporidium parvum is an enteric parasite that causes the diarrheal disease cryptosporidiosis in humans and cattle. Öocysts are its encysted, environmental form which is strongly resistant to various environmental stresses. Due to the threat öocysts pose to human health, the transport and removal of öocysts in the environment has been extensively studied using classical column experiments at the bench scale during the past decade. However, the molecular details of the surface chemistry of öocysts are still limited, and the mineral surface adhesion mechanism has not yet been at the molecular scale.

In this study, the surface chemistry and molecular interaction mechanism of öocysts with the ZnSe internal reflection element (IRE) surface was investigated as a function of pH and ionic strength in NaCl and CaCl₂ background electrolyte using in-situ ATR-FTIR spectroscopy coupled with electrophoretic mobility measurements. Because the surface properties of öocysts play an important role in öocyst adhesion behavior, the effects of different surface modifications, including viable, formalin-, and heat-inactivation, were examined. 

Preliminary results from the ATR-FTIR indicate that changes in solution chemistry strongly impact öocysts adhesion behavior in aqueous systems. Increasing ionic strength (1-100 mM) or decreasing pH (9.0–3.0) resulted in significantly increase in öocysts adhesion to the IRE surface. Higher adhesion rate was observed in CaCl₂ solution than in NaCl solution at the same ionic strength due to the cation bridging effect of Ca²⁺. The data indicate that both formalin and heat inactivation increased the ratio of amide I to amide II, an important indicator of the conformation of surface protein structure. Protein secondary structure conformation was also observed with the modification. The amide I band at 1635 cm^-1 in viable öocysts suspension shifted to 1626 cm^-1 in heat inactivated öocysts suspension, indicating the change of the protein secondary structure from parallel β-sheet to anti-parallel β-sheet.