Gentamicin- and neomycin-resistant mutants of Escherichia coli K-12 cross-resistant to nitrofurans.

Gentamicin and neomycin-resistant mutants of Escherichia coli K-12 were isolated some of which were resistant to nitrofurans, chlorate, P1 and lambda bacteriophages as well as to all aminoglycoside antibiotics tested. Previously isolated nitrofuran-resistant mutants were not cross-resistant to the tested aminoglycosides, chlorate and bacteriophages. The aminoglycoside-resistant mutants exhibiting cross-resistance had enhanced membrane Mg2+-ATPase and decreased periplasmic alkaline phosphatase activity compared to their parent sensitive strains. The mutants were also defective in the fermentation of sugars, reduction of nitrate and nitrite, and in formate dehydrogenase activity. Preliminary genetic studies indicated that the pleiotropic mutation might be located in the upper left quadrant of the E. coli K-12 chromosome linkage map. It is postulated that such mutants with gross membrane alterations have impaired accumulation of aminoglycoside and nitrofuran antibiotics.