Characterization of Three Plasmid Deoxyribonucleic Acid Molecules in a Strain of Streptococcus faecalis : Identification of a Plasmid Determining Erythromycin Resistance

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Abstract
Three plasmids designated α, β, and γ, distinguishable by their molecular weights (6, 17, and 34 million, respectively) were isolated from Streptococcus faecalis strain DS-5 (ATCC 14508). Derivatives of this strain “cured” for erythromycin resistance lacked the β-plasmid. In the parent strain the β-plasmid was estimated to be present to the extent of one to two copies per chromosomal genome equivalent whereas the α- and γ-plasmids were about nine and five copies, respectively.