Experimental adhesion of Geobacillus stearothermophilus and Anoxybacillus flavithermus to stainless steel compared with predictions from interaction models

Spore-forming thermophilic bacteria of the genus Geobacillus and Anoxybacillus are frequent contaminants in dairy industry. This study is the first attempt to apply models of physicochemical interactions (thermodynamic, DLVO, and XDLVO) to quantify their adhesion properties to stainless steel particles (SSP). The predictions of interaction models were compared with experimental data (contact angles, zeta potentials, size) regarding interacting surfaces (cells and SSP). Adhesion intensities (AI) were determined experimentally taking advantage of the magnetic properties of particulate stainless steel. The importance of weak physicochemical interactions was estimated by comparison of experimental AI with model predictions of colloidal interactions. The results revealed that the most reliable description of AI was obtained using the XDLVO model, including Lifshitz–van der Waals (LW), acid–base, and electrostatic (EL) interactions. The AI of cells to SSP at an ionic strength of 10 mM decreased in the order G. stearothermophilus DSM 456 > A . flavithermus DSM 2641 > G . stearothermophilus DSM 22, and the differences were statistically significant. At a higher ionic strength (100 mM), the highest AI was observed for A . flavithermus DSM 2641, but the differences between species studied were statistically insignificant. The main driving force for bacterial adhesion to SSP at 10 mM was EL interactions, while at 100 mM, the XDLVO model predicted favorable interactions between A . flavithermus DSM 2641 and SSP due to attractive LW forces.