Tetracycline resistance in periodontal pathogens.

Antimicrobial agents are used in combination with debridement to eliminate putative periodontal pathogens, including Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans, from diseased tissues. The most frequently used antimicrobial agents are the tetracyclines. However, these agents are not effective in some patients. This lack of efficacy may be due to antimicrobial resistance. As many as 75% of the bacteria in the subgingival flora may be resistant to tetracycline after long-term, low-dose treatment. Tetracycline resistance is mediated by the tet(M) determinant in some isolates of Veillonella species and Fusobacterium nucleatum, while a DNA probe to the tet(Q) determinant hybridizes to isolates of Prevotella denticola and P. intermedia. The mechanism of tetracycline resistance for most periodontal organisms, however, has yet to be determined. Before tetracycline is used as adjunctive therapy for refractory periodontitis, the subgingival bacterial flora should be tested for susceptibility.