Iron-chelating activity of tetracyclines and its impact on the susceptibility of Actinobacillus actinomycetemcomitans to these antibiotics

Three tetracyclines (tetracycline, doxycycline, and minocycline) were found to possess iron-chelating activity in a colorimetric siderophore assay. De termination of MICs indicated that the activity of doxycycline against the periodontopathogen Actinobacillus actinomycetemcomitans was only slightly i nfluenced by the presence of an excess of iron that likely saturates the an tibiotic. On the other hand, the MICs of doxycycline and minocycline were s ignificantly lower for A. actinomycetemcomitans cultivated under iron-poor conditions than under iron-rich conditions.