Enhancement of R-plasmid-determined resistance to aminoglycoside antibiotics by R-plasmid nitrofurantoin resistance in Escherichia coli.

Transfer of an R-plasmid, which confers nitrofurantoin resistance (by decreasing host strain nitrofurantoin reductase activity) to Escherichia coli K12 conferring R-plasmid aminoglycoside antibiotics resistance, increased the aminoglycoside resistance level several fold. An F' (Lac+, leu+, thr+, pro+, Gal+ Mal+) plasmid decreased the nitrofuran resistance level, annuled the increased aminoglycoside resistance and restored nitrofuran reductase activity in the transconjugants.