Analysis of a plasmid-coded carbadox resistance determinant of Escherichia coli

A carbadox (Cdx) resistance determinant coded by Escherichia coli R-plasmid pNV13 (50 kb, Ap, Sm/Sp, Cdx^R) was localized on a 1.3-kb DNA fragment. The gene product expressed from this fragment in minicells of E. coli was a 16-kDa soluble protein. The nucleotide sequence revealed an open reading frame for a 14-kDa protein. Resistance to Cdx seemed to result from successive reduction of the two N-oxide groups of Cdx, and also to depend on other (host) factors, since the original E. coli isolate, NV13, retained high-level Cdx resistance after being cured of plasmid pNV13.