PCR monitoring for tetracycline resistance genes in subgingival plaque following site-specific periodontal therapy - A preliminary report

Background: The selection of antibiotic resistance genes during antibiotic therapy is a critical problem complicated by the transmission of resistance genes to previously sensitive strains via conjugative plasmids and transpo sons and by the transfer of resistance genes between gram-positive and gram -negative bacteria. The purpose of this investigation was to monitor the pr esence of selected tetracycline resistance genes in subgingival plaque duri ng site specific tetracycline fiber therapy in 10 patients with adult perio dontitis. Method: The polymerase chain reaction (PCR) was used in separate tests for the presence of 3 tetracycline resistance genes (tetM, tetO and tetQ) in DN A purified from subgingival plaque samples. Samples were collected at basel ine, i.e., immediately prior to treatment, and at 2 weeks, and 1, 3, and 6 months post-fiber placement. The baseline and 6-month samples were also sub jected to DNA hybridization tests for the presence of 8 putative periodonta l pathogenic bacteria. Results: PCR analysis for the tetM resistance gene showed little or no chan ge in 5 patients and a decrease in detectability in the remaining 5 patient s over the 6 months following tetracycline fiber placement. The results for tetO and tetQ were variable showing either no change in detectability from baseline through the 6-month sampling interval or a slight increase in det ectability over time in 4 of the 10 patients. DNA hybridization analysis sh owed reductions to unmeasurable levels of the putative periodontal pathogen ic bacteria in all but 2 of the 10 patients. Conclusions: These results complement earlier studies of tet resistance and demonstrate the efficacy of PCR monitoring for the appearance of specific resistance genes during and after antibiotic therapy.