Changes in Sodium, Calcium, and Magnesium Ion Concentrations That Inhibit Geobacillus Biofilms Have No Effect on Anoxybacillus flavithermus Biofilms

Abstract

ABSTRACTThis study investigated the effects of varied sodium, calcium, and magnesium concentrations in specialty milk formulations on biofilm formation byGeobacillusspp. andAnoxybacillus flavithermus. The numbers of attached viable cells (log CFU per square centimeter) after 6 to 18 h of biofilm formation by three dairy-derived strains ofGeobacillusand three dairy-derived strains ofA. flavithermuswere compared in two commercial milk formulations. Milk formulation B had relatively high sodium and low calcium and magnesium concentrations compared with those of milk formulation A, but the two formulations had comparable fat, protein, and lactose concentrations. Biofilm formation by the threeGeobacillusisolates was up to 4 log CFU cm−2lower in milk formulation B than in milk formulation A after 6 to 18 h, and the difference was often significant (P≤ 0.05). However, no significant differences (P≤ 0.05) were found when biofilm formations by the threeA. flavithermusisolates were compared in milk formulations A and B. Supplementation of milk formulation A with 100 mM NaCl significantly decreased (P≤ 0.05)Geobacillusbiofilm formation after 6 to 10 h. Furthermore, supplementation of milk formulation B with 2 mM CaCl2or 2 mM MgCl2significantly increased (P≤ 0.05)Geobacillusbiofilm formation after 10 to 18 h. It was concluded that relatively high free Na+and low free Ca2+and Mg2+concentrations in milk formulations are collectively required to inhibit biofilm formation byGeobacillusspp., whereas biofilm formation byA. flavithermusis not impacted by typical cation concentration differences of milk formulations.