Interactive Forces between Co-aggregating and Non-co-aggregating Oral Bacterial Pairs

The temporo-spatial development of plaque is governed by adhesive interactions between different co-aggregating bacterial strains and species. Physico-chemically, these interactions are due to attractive Lifshitz-Van der Waals and acid-base forces, and occur despite electrostatic repulsion and with a critical influence of temperature. The forces between co-aggregating and non-co-aggregating pairs have never been measured, however. The aim here, thus, is to investigate, by atomic force microscopy, whether there is a difference in interactive forces between co-aggregating and non-co-aggregating bacterial pairs at 10°C, 22°C, and 40°C. Actinomyces naeslundii 147 was immobilized on poly-L-lysine-coated tipless AFM cantilevers, while streptococci were immobilized on poly-L-lysine-coated glass surfaces. Upon approach, a repulsive force was measured, regardless of whether a co-aggregating or non-co-aggregating pair was involved. However, upon retraction, the co-aggregating pair exhibited larger adhesive forces and energies than did the non-co-aggregating pair. Adhesive interactions between the co-aggregating pair were smallest at 40°C.