Adhesion of anaerobic beer spoilage bacteria Megasphaera cerevisiae and Pectinatus frisingensis to stainless steel

• Pectinatus and Megasphaera are responsible for 30% of beer spoilage.
• They are common inhabitants of biofilms in brewery bottling halls.
• Adhesion of Pectinatus and Megasphaera was studied theoretically and experimentally.
• The lowest adhesion to stainless steel was at pH 12 and low ionic strength.
• Independently of pH, adhesion could be suppressed by high ionic strength.

Although adhesion of acetic and lactic acid bacteria and yeasts have been extensively studied in a wide range of experimental and theoretical approaches, no attention has been paid to adhesion of anaerobic beer spoilage bacteria to solid materials. This work focuses on physicochemical aspects of adhesion of Megasphaera cerevisiae and Pectinatus frisingensis to stainless steel. The results, based on experimental characterization of surface properties, contact angle and zeta potential measurements, are used in modeling the surface interactions (thermodynamic and colloidal models) resulting in a quantitative prediction of interactions. The model predictions are compared with experimental adhesion tests in order to identify physicochemical forces controlling adhesion. The results revealed that the most significant adhesion occurred at a low ionic strength (10 mM) and an acidic to neutral pH. Under these conditions cell/stainless steel interactions were more pronounced for M. cerevisiae than for P. frisingensis and were influenced mostly by electrostatic attractions between surfaces. Overall, the lowest rate of adhesion between cells and stainless steel was observed at a low ionic strength and an alkaline pH. At high ionic strength (500 mM), adhesion was more pronounced for P. frisingensis, demonstrating the importance of Liftshitz-van der Waals interactions.