Figure 3. Bacteria-hydroxyapatite interaction. (A-C) Optical photomicrographs (bar = 50 µm) of suspensions containing HAP and L. salivarius (A,B) or L. casei (C). In (A), no Ca²⁺ was added; in (B) and (C), [Ca²⁺] = 1 x 10^–2 mol L^–1. (D) Scanning electron microscope micrograph of suspensions containing L. salivarius and hydroxyapatite with [Ca²⁺] = 1 x 10^–2 mol L^–1 (bar = 1 µm).