TETRACYCLINE-RESISTANT MICROORGANISMS RECOVERED FROM PATIENTS WITH REFRACTORY PERIODONTAL-DISEASE

Tetracycline in combination with scaling and root planing is frequentl y used to treat refractory periodontal disease. This study examined te tracycline resistance in bacteria recovered from periodontal pockets o f patients with refractory periodontitis. Bacterial isolates resistant to 10 mu g/ml of tetracycline were isolated from plaque samples of 17 patients, of whom 6 had received tetracycline within 8 weeks prior to sampling. Minimal inhibitory concentrations (MICs) of tetracycline an d minocycline were determined by agar dilution. In the 6 patients who had received tetracycline, a mean of 22.9% (+/- 38.2) of the total cul tivable subgingival flora were resistant to tetracycline, compared wit h a mean of 7.2% (+/- 8.5) in the untreated group. Although various or ganisms were isolated, in most patients, the tetracycline-resistant or ganisms were dominated by Streptococcus spp. Overgrowth of Candida was found in one patient, and of Enterobacteriaceae in another patient, w hile small numbers of yeast or Staphylococcus spp. were isolated from the plaque samples of 9 others. 3 out of 4 patients who did not respon d to tetracycline treatment had a variety of tetracycline-resistant an aerobic Gram-negative rods present. No correlation was found between i ncreased proportions of tetracycline resistance in the whole bacterial sample and the presence of resistant periodontal pathogens.