Streptcoccus mutans DL5, isolted from the dental plaque of a pig, was resstant to high levels of streptomycin (Sm, 20 mg/ml), erthromycin (Em, 1 mg/ml), and tetracydine (Tc, >100 pg/ml), but ontaine no detectable plasndd DNA. The Smr and Emr determinants were doned from celluar DNA on the self-replicating 5- Lett. 4:153-160, 1987). A 1.67kbp NdeI ftgment, internal to the ORF from strain DLS, as well as pDL421 hybridized under sngent co ns to DNA from 10 of 10 Tcr strains of C. coli and Canpylobacter jejuni from human and animal sources, but not to DNA from Tce isdates of these two species.Bacterial tetracycline resistance (Tc7) is encoded by a diversity of genetic determinants. Levy and associates (15,21)