[Changes in the activity of antibiotics by fatty acids in bone tissue]

The C14 to C18 fatty acid content of spongious bone was measured by gas-liquid chromatography. Palmitic acid (C16:0), oleic acid (C18:1) and linoleic acid (C18:2) represented 20 to 40% of the total free fatty acid concentration (30 mM/l). Linoleic acid was found to have the greatest bacteriostatic activity against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa strains. The effect of linoleic acid-gentamicin combination was synergistic against S. aureus. In contrast, both gentamicin and colistin activities were highly antagonized by linoleic and oleic acids against E. coli and P. aeruginosa strains. These different effects of free fatty acids on antibiotic activity could be explained, in part, by a change in permeability of bacterial cells. The clinical implications of these results in bone infections are discussed.