Interactions of group H resistance factors with the F factor.

The four R factors described in this paper form a single compatibility group which has been previously designated group H. Recombination was demonstrated between any pair of the plasmids TP117, 123, and 124. In contrast, TP116 did not appear to recombine with any other members of the group. TP117, 123, and 124 usually displaced the F factor from Escherichia coli K-12F(+), while TP116 and F coexisted stably in that strain. Deoxyribonucleic acid reassociation experiments showed minimal homology between F and the four group H plasmids. The results indicate that there are limitations to using incompatibility alone for classification of bacterial plasmids.