The effects of chlorate- and streptomycin-resistance mutations on nitrofurantoin resistance in Escherichia coli K-12.

Chlorate-resistant mutants with none of the usual pleiotropic effects such as defective nitrate reductase activity were isolated from Escherichia coli K-12. These chlorate-resistant mutants (designated chlHW) did not yield strains with a high level of nitrofurantoin resistance following selection with nitrofurantoin. The chlorate-resistance mutation reduced the nitrofurantoin resistance of high-level mutants to an intermediate level. Further mutation to resistance to streptomycin and other aminoglycoside antibiotics suppressed the effect of chlHW on the level of nitrofurantoin resistance. Other chlorate-resistance genes examined did not have the same effect on nitrofurantoin resistance as chlHW. The gene was cotransducible (Pl) with intermediate-level nitrofurantoin resistance and proC. It is suggested that the chlHW mutation may enhance the accumulation of nitrofurantoin inside the cell since it is known that a multiple aminoglycoside-resistance mutation with pleiotropic effects on the cell membrane can also confer high-level resistance to nitrofurantoin.

The enhancement of R-plasmid-mediated resistance to aminoglycoside antibiotics by mutations to nitrofurantoin resistance in Escherichia coli.

Mutation to high level resistance to nitrofurantoin of a strain of Escherichia coli carrying an R-plasmid conferring resistance to gentamicin, kanamycin and other antibiotics resulted in greatly increased resistance to the two aminoglycosides but not the other antibiotics. A similar result was observed when the R-plasmid was transferred to high level nitrofurantoin-resistant mutants. The enhanced resistance was accompanied by a 30% increase in 3-N-acetyltransferase activity. Resistance to chloramphenicol in a strain carrying an R-plasmid coding for chloramphenicol acetyltransferase was not increased although the same strain showed increased resistance to kanamycin. These observations may have considerable significance in the development of resistance to gentamicin and other aminoglycoside antibiotics.

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.

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.

Transferable nitrofuran resistance conferred by R-plasmids in clinical isolates of Escherichia coli.

A high proportion of nitrofuran-resistant strains has been found in a collection of antibiotic-resistant Gram-negative bacteria isolated from patients with urinary tract infections. Some of the Escherichia coli carried R-plasmids that conferred resistance to nitrofurantoin and nitrofurazone. The mechanism of resistance is not clear; only in lactose non-fermenting recipients was there a decrease in the nitrofuran-reducing ability of whole-cell suspensions. One of the plasmids conferred enhanced resistance to UV light on DNA repair defective mutants but not on repair efficient strains. In some resistant strains, the total resistance was apparently the result of a combination of chromosomal and plasmid-borne genes. The presence of the plasmid may allow the development of higher resistance levels by mutation of chromosomal genes.

Mutations to nitrofurantoin and nitrofurazone resistance in Escherichia coli K12.

The isolation and properties of nitrofurantoin- and nitrofurazone-resistant mutants have been compared. Nitrofurantoin-resistant mutants were easier to obtain and showed a higher resistance level. There was some cross-resistance at lower drug concentrations but not at higher levels. There was no difference in the UV resistance of most of the mutants obtained although a recB strain, AB2470, did yield nitrofurantoin-resistant mutants with increased UV resistance. This was however the only repair-defective strain which could be mutated to nitrofurantoin resistance. It is suggested that there is a mechanism for nitrofurantoin resistance in Escherichia coli K12 which does not confer resistance to nitrofurazone and which may be associated with the repair of damaged DNA. This mechanism is in addition to that which also confers resistance to nitrofurazone.