[Tetracycline resistance in oral microorganisms in patients with periodontal disease].

Several longitudinal studies have shown that periodontal treatment consisting of surgical and/or nonsurgical debridement of the teeth often is sufficient to prevent continued attachment loss when the patients' oral hygiene measures are good. Nevertheless, some patients will, in spite of excellent oral hygiene measures, continue to show attachment loss. The treatment of these patients has mainly been empirical, and the clinicians have used different kinds of antibiotics for different time intervals to eliminate proposed periodontal pathogens. The preferred antibiotic has been tetracycline. Most bacteria associated with destructive periodontal disease will normally be susceptible to tetracycline at the levels achieved in the gingival crevicular fluid after systemic administration of the antibiotic. Some patients have a microbial flora that will not change enough or be inhibited by these substances. The reason for this may in many cases be the development of antimicrobial resistance. Today 14 genotypes of tetracycline resistance have been found. The resistance is one of three types: active secretion, protection of the ribosomes by proteins and an active breakdown of tetracycline. The third type has recently been discovered as a cryptic gene in the microorganism Bacteroides fragilis. This gene is only expressed after transfer to Eschericia coli. Active breakdown of tetracycline does normally not occur in nature and the global level of the drug is increasing since tetracycline is the second most used antibiotic in the world today. It is therefore of interest to identify tetracycline resistance determinants in the oral cavity and to compare these with tetracycline resistance genes from other sources of human, animal and environmental origin.