Filtration–elution of Cryptosporidium oocysts assisted by electrostatic interactions

The goal of the present study was to investigate the interfacial phenomena that govern the interactions between Cryptosporidium parvum oocysts and synthetic filtration media, in order to define guidelines to improve the choice of appropriate materials and filtration–elution conditions. Three frequently used filtration media were studied: polycarbonate and cellulose-ester membranes, and a polyethersulfone cartridge. The electrokinetic potential of Cryptosporidium oocysts and of the filtration media were measured by electrophoresis and streaming potential, respectively. Aqueous media such as dilutions of a phosphate buffer (PBS), NaCl, CaCl2 at various concentrations and pH, were tested. The highest recovery rates, close to 100%, were obtained in conditions where the electrokinetic potentials of both the membrane and the oocysts were at maximum negative values. This condition was met using a polycarbonate membrane and low concentrations of monovalent salt. The media generally used in microbiology, such as phosphate buffer or 8 g l−1 KCl or NaCl, caused irreversible adhesion and dramatic decrease in recovery rates.