Nitrofuran reductase activity in nitrofurantoin-resistant strains of Escherichia coli K12: some with chromosomally determined resistance and others carrying R-plasmids.

The nitrofuran reductase activity of Escherichia coli K12 strains was separated into two components by passage through Sepharose 4B-200. The components differed in their sensitivity to 2 M urea and their reactivity with NADH and NADPH. Some nitrofurantoin-resistant mutants had lost one component (alpha) while retaining the other (beta). Other mutants, resistant to higher levels of nitrofurantoin, had lost most of the beta component as well. Transconjugants which had received plasmids conferring nitrofurantoin resistance were found to have only the alpha component and it was markedly less active when NADH rather than NADPH was supplied as co-enzyme.