FIG. 5.

Comparison of mathematical calculations and experimental data for membrane-bound vancomycin. (A) Amount of bound vancomycin located at the innermost segment (cytoplasmic membrane) of cells with thick cell walls, calculated with both a standard reaction-diffusion equation (broken line) and a clogging model (solid line). (B) The amount of membrane-bound vancomycin was determined for both cells with thin cell walls and cells with thick cell walls. Cell preparations with thin (open circles) and thick (closed circles) cell walls were exposed to vancomycin for 2.5, 5, 15, 30, and 60 min and were used to determine membrane-bound vancomycin concentrations by microbiological assay and HPLC assay. Membrane-bound vancomycin levels increased in accordance with vancomycin exposure time, and the curve of the increment shows an upward-convex shape, which coincides with theoretical curves developed by introducing the clogging factor (solid line in panel A).