Influence of ionic strength and pH on hydrophobicity and zeta potential of Giardia and Cryptosporidium

Surface charge and hydrophobicity of microorganisms are involved in interfacial interaction of cells, such as flocculation and adhesion. The calculated zeta potentials of Giardia cysts and Cryptosporidium oocysts in waters at neutral pH were on average - 17 and - 38 mV, respectively. The isoelectric points of cysts and oocysts were estimated as pH 2.2 and pH 3.3, respectively. The hydrophobicities of cysts and oocysts, obtained from the microbial adherence to hydrocarbons (MATH) test, were determined by initial removal rate. Although the initial removal rates of oocysts were larger than those of cysts in all trials, both demonstrated marked hydrophobicity. The hydrophobicities were significantly increased with decreasing pH for both protozoa.