An electron microscopic study of the effect of clindamycin on adherence of Staphylococcus aureus to bone surfaces.

Discs of rabbit tibia, 5 mm thick, were utilized to study the adherence of Staphylococcus aureus to the bone surface in the presence and absence of clindamycin. Bacteria were grown in broth media containing the bone slices and varying concentrations of clindamycin. In the absence of the antibiotic, S. aureus adhered extensively to bone surfaces and formed large microcolonies which were surrounded by an amorphous matrix. In the presence of 0.025 micrograms/ml of clindamycin (0.1 MIC), S. aureus adhered less to bone surfaces, forming smaller and fewer microcolonies. In the presence of 0.0625 micrograms/ml of clindamycin (0.25 MIC), S. aureus adhered to the bone surfaces only sparsely, forming small microcolonies with very little matrix holding them together, and leaving very large areas of the bone surface uncolonized. In the presence of 0.125 micrograms/ml of clindamycin (0.5 MIC), bone surfaces were basically clean, with only one or two cells (no microcolonies) found in crevices and indentations of the bone surface. In the presence of 0.25 micrograms/ml (1 MIC) no bacteria adhered to the bone surfaces.