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

This study investigated the effects of varied sodium, calcium, and magnesium concentrations in specialty milk formulations on biofilm formation byGeobacillus spp. 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 ofGeobacillus and three dairy-derived strains ofA. flavithermus were 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 threeGeobacillus isolates was up to 4 log CFU cm−2 lower 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. flavithermus isolates were compared in milk formulations A and B. Supplementation of milk formulation A with 100 mM NaCl significantly decreased (P ≤ 0.05)Geobacillus biofilm formation after 6 to 10 h. Furthermore, supplementation of milk formulation B with 2 mM CaCl2 or 2 mM MgCl2 significantly increased (P ≤ 0.05)Geobacillus biofilm 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 byGeobacillus spp., whereas biofilm formation byA. flavithermus is not impacted by typical cation concentration differences of milk formulations.