3 SUBTYPES OF THE TET(M) GENE IDENTIFIED IN BACTERIAL ISOLATES FROM PERIODONTAL POCKETS

The tet(M) genes were characterized from 84 isolates of 10 different b acterial spe cies isolated from the periodontal pockets of 16 patients with periodontal disease. A 740 bp polymerase chain reaction product from the hypervariable region of the tet(M) structural gene was cleave d with the restriction enzymes AluI and HinfI. Three different restric tion patterns were identified for each of the two enzymes. By DNA sequ encing, using a direct solid-phase automated sequencing method, the is olates could be grouped into 3 different clusters of tet(M) subtypes. The internal DNA homology within each subtype was 98-100%; the homolog y between clusters was 89-94%. Two different subtypes were identified in 9 of 10 bacterial species, and the remaining species had 3 differen t subtypes. One of the subtypes (M3) was seen mainly in the anaerobic isolates. This subtype was different from all earlier sequenced struct ural tet(M) genes present in the Genbank. Most patients had two differ ent subtypes of tet(M), and a third subtype was seen in the 3 patients who exhibited the greatest variety of tetracycline-resistant bacteria l species. It appears that the presence of one subtype of the tet(M) g ene within a patient or bacterial species does not prevent the acquisi tion of another subtype of the same gene. This study identified a new subtype of the tet(M) gene and grouped it into 3 distinct yet highly h omologous genetic subtypes.