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Evidence for Conjugal Transfer of a Streptococcus faecalis Transposon (Tn916) from a Chromosomal Site in the Absence of Plasmid DNA
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1981
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Microbial PathogensBacteriologyMolecular BiologyAntibiotic ResistanceBacterial PathogensDrug ResistanceConjugal TransferAnn ArborTc ResistancePlasmid DnaAntibacterial MechanismsInfection ControlAntimicrobial ResistanceHealth SciencesAntimicrobial Drug DiscoveryDrug Resistance AnalysisChromosomal SiteMolecular MicrobiologyBacterial ResistanceClinical MicrobiologyAntimicrobial Resistance GeneAntimicrobial SusceptibilityAntibioticsMicrobiologyAntimicrobial PharmacodynamicsMedicineSt. JosephMicrobial Genetics
Streptococcus faecalis strain DS16, a multiply drugresistant clinical isolate obtained from St. Joseph's Mercy Hospital (Ann Arbor), was previously shown to harbor two plasmids (Clewell et al. 1978; Tomich et al. 1979b). One of the plasmids, pAD1 (35 megadaltons [MD]), is conjugative and determines hemolysin and bacteriocin activities; the other plasmid, pAD2 (15 MD), is nonconjugative and determines resistance to streptomycin (Sm), kanamycin (Km), and erythromycin (Em) (inducible). The last resistance is located on a transposon (Tn917) that can be induced to transpose by exposing the cells to a low (0.5 µg/ml) concentration of erythromycin (Tomich et al. 1979a, 1980). A tetracycline-resistance (Tcr) determinant was presumed to be chromosome-borne, since derivatives cured of pAD1 and pAD2 and devoid of plasmid DNA (on the basis of physical analysis) maintained a resistance to Tc (minimum inhibitory concentration was 30 µg/ml). We report here that the Tc resistance is located on a transposon...