Acridine treatment of F+and Hfr strains ofEscherichia coli K12carrying a neomycin-kanamycin resistance determinant

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Abstract
The F factor and the K resistance determinant form an R factor (KF) in E. coli K12. In this R factor the two plasmids are independent of each other and occupy different attachment sites in the host cell.Treatment of an F+(K) strain with acriflavine and acridine orange yielded the following classes: F+K−; F−K+; and F−K−. The K determinant was thus curable independently of F, which supports the hypothesis of independence of the two plasmids. In Hfr(K) strains, K remains curable with acridines while F is immune. Thus, K remains independent of F in both the F+ and Hfr states.The use of higher concentrations of acridine orange than those needed for cure of K in the F+(K) strain resulted in no elimination of K, although the F factor was absent from all surviving lines tested. It is suggested that this is caused by equal inhibition of replication of both the chromosome and K, and greater inhibition of that of F.