Sorption of Streptococcus suis on various soil particles from an Alfisol and effects on pathogen metabolic activity

The potential contamination of soil environments by pathogens from agricultural manures has received great attention in recent years. However, few studies of the sorption and metabolic activity of pathogens on soil particles have been conducted to date. In this study, we investigated the sorption of pathogen Streptococcus suis on various soil particles from an Alfisol as a function of pH and calcium chloride (CaCl2) concentration. S. suis metabolic activity in the presence of different soil particles was also studied by micro-calorimetric techniques. The amount of S. suis sorbed followed the order: inorganic clay > organic clay > inorganic silt > organic silt > inorganic sand > organic sand. Zeta potentials of S. suis were negative over the experimental conditions and increased with the decrease of pH or the increase of Ca2+ concentrations. A gradual decrease in the sorption of S. suis on soil particles was observed with the increase of pH from 4.0 to 9.0. Increasing Ca2+ concentrations (01 mm) resulted in an increase of S. suis sorption on clays, silts and sands, while larger Ca2+ concentrations (2050 mm) depressed S. suis sorption on silts and sands. The exponential growth of S. suis was stimulated by silts and sands, but inhibited by clays. Our results show that electrostatic forces play a major role in the sorption behaviour and that an additional non-DLVO type interaction (electrosteric repulsion) occurs at large Ca2+ concentrations. Different sorption affinities of S. suis on soil particles may be the dominant factor influencing S. suis activities.