Western Society of Periodontics

Laboratory Studies

Volume Number 4, 1995

Tetracyline-resistant microorganism recovered from patients with refractory periodontal disease

The purpose of this study was to examine tetracycline resistance in patients with periodontal disease refractory not only to periodontal treatment but also to tetracycline treatment when this drug was prescribed in addition to conventional periodontal treatment. Bacterial isolates resistant to 10 ~g/ml of tetracycline were isolated from plaque samples of 17 patients, of whom six had received tetracycline within eight days prior to sampling. Minimal inhibitory concentrations (MIC) of tetracycline and minocycline were determined by agar dilution. In the six patients who had received tetracycline, a mean of 22.9% of the total cultivable subgingival flora were resistant to tetracycline, compared with a mean of 7.2% in the untreated group. Although various organisms were isolated, in most patients the tetracycline-resistant organisms were dominated by Streptococcus species. Overgrowth of Candida was found in one patient, and of Enterobacteriaceae in another patient, while small numbers of yeast or Staphylococcus species were isolated from the plaque samples of nine others. Three out of four patients who did not respond to tetracycline treatment had a variety of tetracycline-resistant anaerobic Gram-negative rods present. No correlation was found between increased proportions of tetracycline resistance in the whole bacterial sample and the presence of resistant periodontal pathogens. The authors conclude that a few limitations to interpretations apply to this study. Although the transport medium used has proved successful in keeping anaerobes alive for several days, some strict anaerobes may not survive in this environment for more than a few hours. [M.O.]