Characterization of three plasmid deoxyribonucleic acid molecules in a strain of Streptococcus faecalis: identification of a plasmid determining erythromycin resistance

Three plasmids designated α, β, and γ, distinguishable by their molecular weights (6, 17, and 34 million, respectively) were isolated from S. 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.