TETRACYCLINE RESISTANCE IN PREVOTELLA ISOLATES FROM PERIODONTALLY DISEASED PATIENTS IS DUE TO THE TET(Q) GENE

Tetracycline-resistance in gram-negative periodontal bacteria is often due to the presence of the tet(Q) gene. In the present study the poly merase chain reaction (PCR) was used to examine 54 isolates of gram-ne gative anaerobic rods (Prevotella intermedia, Prevotella nigrescens an d related or Bacteroides-like species) for the presence of the tet(Q) gene. The isolates were recovered from 42 patients with peri odontal d isease living in northern Europe and North America. An 814 base-pair s egment of the tet(Q) gene was amplified from all 31 isolates resistant to tetracycline with minimal inhibitory concentrations of 4 mu g/ml a nd above. The presence of the tet(Q) gene was verified using hybridiza tion with a specific oligonucleotide internal to the amplified region and restriction endonuclease digestion with DdeI. A PCR product of the same size was also amplified from one tetracycline susceptible isolat e (minimal inhibitory concentration=0.5 mu g/ml). However, this isolat e and the one isolate that was resistant to tetracycline at 4 mu g/ml showed a weaker signal than the remaining isolates when hybridized wit h the internal probe. Typing of the PCR products using restriction end onuclease digests with AluI and HpaII revealed two clusters of distinc t electrophoresis patterns, indicating that two different subtypes of the tet(q) gene were present in this material. A control strain contai ning the tet(q) gene from Bacteroides thetaiotaomicron had a different electrophoresis pattern for AluI. This study indicated that subtypes of the tet(q) gene in tetracycline-resistant gramnegative periodontal bacteria exist both within the same patient and within the same specie s.