Microelectrophoresis of Cryptosporidium parvum oocysts in aqueous solutions of inorganic and surfactant cations

Cryptosporidium parvum is a protozoan parasite associated with waterborne o utbreaks of diarrhoeal disease. The life cycle of this parasite includes th e production of a spheroidal oocyst that is of 4-6 microns in diameter. The thickness of the oocyst wall and its capacity to strongly adhere to both o rganic and inorganic surfaces are features of the oocysts which could be at tributed to its survival in the environment for extended periods. Hence, th e need to study their surface chemistry in the aqueous environment. The sur face charging properties of the intact C. parvum oocysts were derived from microelectrophoresis measurements on these robust biological species. The z eta potentials of Cryptosporidium oocysts were measured in a range of inorg anic electrolyte solutions and in solutions of a multivalent cationic surfa ctant. The surface potential of the oocyst was found to be pH dependent, wi th an isoelectric point in mM NaCl of similar to 2, suggesting the presence of surface carboxylate groups associated with glycoproteins or phosphate g roups. The area/charge for the fully ionised oocysts was found to be simila r to 80 nm(2), corresponding to a total maximum charge of 1.6 x 10(-13) C p er oocyst. The effect of a highly charged novel cage surfactant known as CS 12 on the Cryptosporidium oocyst surface potential provided valuable insigh t into its uptake and possible surface activity. Uptake of CS12 was detecte d at concentrations as low as 2 x 10(-8) M. At similar to 2 x 10(-8) M CS12 the oocyst surface was uncharged and became positively charged at higher c oncentrations. These findings suggest that there could be improvements to c urrent concentration methods by manipulation of the surface charge. (C) 199 9 Elsevier Science B.V. All rights reserved.