RESISTANCE AND CROSS RESISTANCE OF ESCHERICHIA COLI S MUTANTS TO THE RADIOMIMETIC AGENT NITROFURAZONE

CpxA/R-Controlled Nitroreductase Expression as Target for Combinatorial Therapy against Uropathogens by Promoting Reactive Oxygen Species Generation

The antibiotic resistances emerged in uropathogens lead to accumulative treatment failure and recurrent episodes of urinary tract infection (UTI), necessitating more innovative therapeutics to curb UTI before systematic infection. In the current study, the combination of amikacin and nitrofurantoin is found to synergistically eradicate Gram-negative uropathogens in vitro and in vivo. The mechanistic analysis demonstrates that the amikacin, as an aminoglycoside, induced bacterial envelope stress by introducing mistranslated proteins, thereby constitutively activating the cpxA/R two-component system (Cpx signaling). The activation of Cpx signaling stimulates the expression of bacterial major nitroreductases (nfsA/nfsB) through soxS/marA regulons. As a result, the CpxA/R-dependent nitroreductases overexpression generates considerable quantity of lethal reactive intermediates via nitroreduction and promotes the prodrug activation of nitrofurantoin. As such, these actions together disrupt the bacterial cellular redox balance with excessively-produced reactive oxygen species (ROS) as "Domino effect", accelerating the clearance of uropathogens. Although aminoglycosides are used as proof-of-principle to elucidate the mechanism, the synergy between nitrofurantoin is generally applicable to other Cpx stimuli. To summarize, this study highlights the potential of aminoglycoside-nitrofurantoin combination to replenish the arsenal against recurrent Gram-negative uropathogens and shed light on the Cpx signaling-controlled nitroreductase as a potential target to manipulate the antibiotic susceptibility.

Interspecies interaction reduces selection for antibiotic resistance in Escherichia coli

Evolution of microbial traits depends on the interaction of a species with its environment as well as with other coinhabiting species. However, our understanding of the evolution of specific microbial traits, such as antibiotic resistance in complex environments is limited. Here, we determine the role of interspecies interactions on the dynamics of nitrofurantoin (NIT) resistance selection among Escherichia coli. We created a synthetic two-species community comprised of two variants of E. coli (NIT susceptible and resistant) and Bacillus subtilis in minimal media with glucose as the sole carbon source. We show that the presence of B. subtilis significantly slows down the selection for the resistant E. coli mutant when NIT is present and that this slowdown is not due to competition for resources. Instead, the dampening of NIT resistance enrichment is largely mediated by extracellular compounds produced by B. subtilis with the peptide YydF playing a significant role. Our results not only demonstrate the impact of interspecies interactions on the evolution of microbial traits but also show the importance of using synthetic microbial systems in unravelling relevant interactions and mechanisms affecting the evolution of antibiotic resistance. This finding implies that interspecies interactions should be considered to better understand and predict resistance evolution in the clinic as well as in nature.

Nitrofurantoin Combined With Amikacin: A Promising Alternative Strategy for Combating MDR Uropathogenic Escherichia coli

Urinary tract infections (UTI) are common infections that can be mild to life threatening. However, increased bacterial resistance and poor patient compliance rates have limited the effectiveness of conventional antibiotic therapies. Here, we investigated the relationship between nitrofurantoin and amikacin against 12 clinical MDR uropathogenic Escherichia coli (UPEC) strains both in vitro and in an experimental Galleria mellonella model. In vitro synergistic effects were observed in all 12 test strains by standard checkerboard and time-kill assays. Importantly, amikacin or nitrofurantoin at half of the clinical doses were not effective in the treatment of UPEC infections in the G. mellonella model but the combination therapy significantly increased G. mellonella survival from infections caused by all 12 study UPEC strains. Taken together, these results demonstrated synergy effects between nitrofurantoin and amikacin against MDR UPEC.

Molecular mechanisms of collateral sensitivity to the antibiotic nitrofurantoin

Antibiotic resistance increasingly limits the success of antibiotic treatments, and physicians require new ways to achieve efficient treatment despite resistance. Resistance mechanisms against a specific antibiotic class frequently confer increased susceptibility to other antibiotic classes, a phenomenon designated collateral sensitivity (CS). An informed switch of antibiotic may thus enable the efficient treatment of resistant strains. CS occurs in many pathogens, but the mechanisms that generate hypersusceptibility are largely unknown. We identified several molecular mechanisms of CS against the antibiotic nitrofurantoin (NIT). Mutants that are resistant against tigecycline (tetracycline), mecillinam (β-lactam), and protamine (antimicrobial peptide) all show CS against NIT. Their hypersusceptibility is explained by the overexpression of nitroreductase enzymes combined with increased drug uptake rates, or increased drug toxicity. Increased toxicity occurs through interference of the native drug-response system for NIT, the SOS response, with growth. A mechanistic understanding of CS will help to develop drug switches that combat resistance.

Resistance mechanisms against a specific antibiotic class frequently often confer negative cross-resistance to other antibiotic classes, a phenomenon known as collateral sensitivity. This study shows that collateral sensitivity in bacteria can be explained by a combination of several mechanisms that can be exploited to develop drug switches that combat resistance.

EFFECT OF HEAT AND PLATING MEDIUM ON SURVIVAL OF ESCHERICHIA COLI AFTER TREATMENT WITH RADIOMIMETIC CHEMICALS

Zampieri, Antonio (Palo Alto Medical Research Foundation, Palo Alto, Calif.), and Joseph Greenberg. Effect of heat and plating medium on survival of Escherichia coli after treatment with radiomimetic chemicals. J. Bacteriol. 89:931-936. 1965.-Survival of Escherichia coli strain S and its radioresistant mutant R(4) after treatment with mitomycin C, azaserine, nitrogen mustard, 1-methyl-3-nitro-1-nitrosoguanidine, nitrofurazone, and proflavine was studied. With all agents except proflavine, R(4) was more resistant than was S. Survival of strain S was greater on minimal glucose-salts medium than on Penassay (Difco), and greater on the latter than on Tryptone (Difco) agar; survival of S was greater when posttreatment incubation temperature was 45 C than when it was 37 C. Post-treatment plating medium or temperature had no effect on survival of R(4). Visible light did not affect survival of S or R(4). The survival curves of R(4) were exponential; those of S exhibited decreasing sensitivity with time of exposure. With proflavine, photoactivation by visible light was demonstrable, but there was no difference in survival between S and R(4). Survival of either strain was not affected by post-treatment plating medium or incubation temperature.

NITROFURAN DERIVATIVES AS RADIOMIMETIC AGENTS: CROSS-RESISTANCE STUDIES WITH ESCHERICHIA COLI

Mutants of Escherichia coli B selected on the basis of resistance to nitrofurazone, NFT, or ultraviolet light proved to be resistant to all three of these agents. Further tests showed that these mutants are also resistant to three other nitrofuran derivatives, nitrofurantoin, nihydrazone, and furazolidone, but not to nifuroxime. The mutants are also resistant to the chemically dissimilar radiomimetic agent, proflavin. Strain B and all the mutants derived from it are equally sensitive to streptomycin, a non-radiomimetic antibiotic. E. coli strain B/r (resistant to radiation and radiomimetic chemicals) shows the same resistance pattern as the new mutant strains. The results are discussed in terms of what is known concerning the basis for the resistance of strain B/r to ultraviolet light. It is concluded that radiomimetic nitrofurans probably exert their effect on E. coli through damage to DNA.

Radiomimetic property of furazolidone and the caffeine enhancement of its lethal action on the vibrios

Sensitivities of the strains belonging to four vibrio biotypes to the action of furazolidone were investigated. Vibrio cholerae (classical) was most and Vibrio parahaemolyticus least sensitive to this drug. Statistical analyses revealed significant differences between any two of the four types of vibrio in respect of their sensitivity to furazolidone. The drug was radiomimetic in action, the doses of UV light (DUV) and furazolidone (Df) required for 10% survival of the vibrios being correlated by the equation, Df = 0.28 exp. (0.008 DUV). Caffeine exhibited lethal synergism with furazolidone and the synergistic effect depended on the mode of caffeine treatment, the effect being maximum when caffeine was present along with and also after furazolidone treatment. UV spectrophotometric study revealed that caffeine did not bind with native DNA but did so with denatured DNA resulting in a bathochromic shift and a quenching of the caffeine absorption maximum at 209.4 nm. The binding isotherm (Scatchard plot) indicated the presence of a heterogeneity in the binding sites and that the parameters for the strongest mode of bonding were n = 0.254 and k = 7.5 X 10(5) M-1.

Genetics of nitrofurazone resistance in Escherichia coli

Wild-type Escherichia coli cells are sensitive to nitrofurazone (NF) and many other nitrofuran derivatives. A variety of evidence indicated that these compounds are converted to toxic "active" metabolites by reductases present in the bacteria. Sensitive E. coli K-12 acquired threefold-greater resistance to NF in one mutational step. These partially resistant mutants could undergo a second mutation that made them 10 times as resistant as the wild type. Mutation of wild-type strain K-12 to the higher level of resistance in a single step was not observed. The first mutational step was associated with partial loss of reduced nicotinamide adenine dinucleotide phosphate-linked, O(2)-insensitive NF reductase activity, and the second step was associated with loss of the remaining activity. The two-step mutants did, however, contain other NF reductases that were inhibited by O(2) and reduced NF only under anaerobic conditions. We designated the genes that control reductase activity "nitrofuran sensitivity genes" (nfsA and nfsB). Thus, wild-type strains are nfsA(+)nfsB(+), and the resistant double mutants are nfsA nfsB. A variety of crosses established that these genes are both located close to gal, that the most probable sequence is lac nfsB gal nfsA, and that the single-step mutants with an intermediate level of resistance are nfsA nfsB(+). The nfsA(+)nfsB strains contained about 70 to 80% of the wild-type reductase I activity-apparently enough to confer wild-type sensitivity. This reductase activity was resistant to 2 M urea. The nfsA nfsB(+) strains had only 20 to 30% of the wild-type activity, and this residual activity was sensitive to 2 M urea.

Effect of dihydroxymethyl furatrizine on cell division of Escherichia coli

Antibacterial activities of 3-di(hydroxymethyl) amino-6[2-(5-nitro-2-furyl)vinyl]-1,2,4-triazine, (dihydroxymethyl furatrizine) were investigated using mutant strains of Escherichia coli lacking repair systems for DNA damage, i.e. polA, uvrA, uvrA, uvrC, recA, recB, recC and uvrArecA. All of the mutant strains were more sensitive to the drug than the parent sgrains, as was the case with the sensitivity to UV-irradiation. These results indicate that the drug acts lethally on sensitive bacteria by damaging their DNA, and parts of the damaged DNA are repaired by excision and recombinational repair systems. Filamentous cell formation was induced in all strains except the uvrArecA strain by sublethal concentration of the drug, as well as by UV-irradiation. It is possible that the occurrence of the short period of "unbalanced growth" induced by such DNA damaging agents leads to filament formation. In the cells of the double mutant, filament formation was induced by the drug but not by UV-irradiation, and the majority of the filamentous cells formed were multinucleated. This suggests that, in this double mutant, the drug directly reacts with the septation mechinery of the cell envelope, resulting in filament formation. This hypothesis is supported by the electron microscopic observations that septation is interrupted in the filamentous cells induced by the drug.

Mutagenic action of nitrofurans on Euglena gracilis and Mycobacterium phlei

There is a pronounced difference between the action of antibiotics and nitrofurans on Euglena gracilis. Those antibiotics that induce hereditary loss of chloroplasts do so only when they affect dividing cells. On the other hand, nitrofurans induce a mass mutation in both dividing and nondividing cells (under conditions of continuous illumination of cultures). It was found that a breakdown product, 5-nitro-2-furaldehyde, is liberated from furadantin and furoxone. This intermediate is responsible for the observed specific mutagenicity of 5-nitrofuran drugs. The mutagenic action of 5-nitro-2-furaldehyde is very similar to that of nitrosoguanidine. Both compounds induce bleached mutants of E. gracilis when acting on growing or resting cells, regardless of the dark or light conditions. Similarly, both compounds induce reverse mutations in auxotrophic strains of Mycobacterium phlei.

Mutation preventing capsular polysaccharide synthesis in Escherichia coli K-12 and its effect on bacteriophage resistance

A mutant strain of Escherichia coli K-12 was found in which spontaneous mutation to phage T7 resistance occurred at a very low frequency. T7 resistance in the parental strain from which this mutant was derived resulted from a mutation to excess capsular polysaccharide synthesis. The mutation preventing T7 resistance, non-9, inhibited capsule formation when transduced into capsulated strains. The non-9 mutation was cotransducible with his, the gene order in this region being non-9 his Su-1.

Genetic location in Escherichia coli K-12 of the ultraviolet-sensitive mutation uvrD3

A host cell reactivation-negative mutation, uvrD3, in Escherichia coli K-12 is located between ilv and metE.

Mutator gene of Escherichia coli B

An azaserine-resistant derivative of Escherichia coli B/UV, AZA/R(1), was found to carry a mutator gene. This gene, designated mutS1, was mapped by means of conjugation and P1kc-mediated transduction. The mutS1 gene was cotransduced with argB at a frequency of 2.4%; the gene order in this region of the chromosome is thy argB mutS1. To determine whether a relationship commonly exists between azaserine resistance and the mutator property, 12 additional azaserine-resistant derivatives of B/UV were developed and tested for the mutator phenotype. None of the twelve was a mutator strain. The level of azaserine resistance was not increased over that of the recipient parent when mutS1 was transduced to an azaserine-susceptible strain. Reversion studies indicated that mutS1 induced adenosine-ribosylthymine to guanosine-cytidine and guanosine-cytidine to adenosine-ribosylthymine transitions. Because such mutational changes are suppressible with deoxynucleosides when induced by base analogues, an attempt was made to suppress the mutator activity of mutS1 by the addition of deoxyribonucleosides to the medium. No suppression was found. Recombinants were prepared containing mutS1 and the Treffers mutator gene of E. coli K-12. The effect of the mutator genes appears to be additive.

Radiomimetic properties of 2-amnipurine in Escherichia coli

Zampieri, Antonio (Palo Alto Medical Research Foundation, Palo Alto, Calif.), and Joseph Greenberg. Radiomimetic properties of 2-aminopurine in Escherichia coli. J. Bacteriol. 91:1773-1774. 1966.-A radioresistant mutant (R(4)) of Escherichia coli strain S was found to be resistant to 2-aminopurine. The composition of the post-treatment plating medium and temperature of incubation did not influence the sensitivity of R(4) to 2-aminopurine. However, strain S was much more sensitive to 2-aminopurine when plated on tryptone-agar than on minimal glucose-salts-agar. Strain S was also more sensitive when the post-treatment incubation was at 37 C than at 45 C. When E. coli strain S was treated with sufficient 2-aminopurine to permit only 10(-5) survivors, 67% of the survivors were resistant to ultraviolet light and to radiomimetic compounds. 2-Aminopurine induced filaments in radiation-sensitive, but not radiation-resistant, strains of E. coli. It is concluded that 2-aminopurine, a base analogue which induces transition mutations, is radiomimetic in several properties.

Cross-resistance relationships in Escherichia coli between ultraviolet radiation and nitrous acid

Zampieri, Antonio (Palo Alto Medical Research Foundation, Palo Alto, Calif.), and Joseph Greenberg. Cross-resistance relationships in Escherichia coli between ultraviolet radiation and nitrous acid. J. Bacteriol. 87:1094-1099. 1964.-A number of radiosensitive and radioresistant strains of Escherichia coli were tested for sensitivity to injury by nitrous acid. All the radioresistant strains, including 13 radioresistant mutants of strain S, B/r, Bpr5, and K-12, were found to be significantly more resistant to nitrous acid than were the radiosensitive strains S and B. The radioresistant mutants of strain S, Bpr5, and K-12 displayed similar responses to nitrous acid and were less resistant than was strain B/r. Strains B and S were indistinguishable on the basis of nitrous acid sensitivity. The survival curves of all strains examined were similar in shape to corresponding survival curves after ultraviolet radiation. The sensitivity to nitrous acid of the radiosensitive strains S and B, but not that of the radioresistant strains, was found to be greater on Tryptone medium than on Penassay medium, and greater on Penassay medium than on glucose-salts medium. Between 2 and 3% of the strain S survivors of nitrous acid treatment were radioresistant; 46 such radioresistant mutants were isolated and found to be identical in cross-resistance pattern with radioresistant types (R(3), R(4), or R(6)) previously described. The proportions in which these radioresistant types were found to occur were similar to those observed after selection by other radiomimetic agents.

RESISTANCE AND CROSS-RESISTANCE OF ESCHERICHIA COLI S MUTANTS TO THE RADIOMIMETIC AGENT PROFLAVINE

Woody-Karrer, Pearl (Palo Alto Medical Research Foundation, Palo Alto, Calif.), and Joseph Greenberg . Resistance and cross-resistance of Escherichia coli S mutants to the radiomimetic agent proflavine. J. Bacteriol. 87: 536–542. 1964.—All 50 of the first-step mutants of Escherichia coli S selected for resistance to proflavine were resistant to ultraviolet light and each of five different radiomimetic chemicals. The mutants were classified into eight types on the basis of their relative resistance to six different radiomimetic drugs and on the basis of the shape of their ultraviolet survival curves. Three of these types are identical to types previously isolated with other radiomimetic drugs; five of the types are new. A high proportion of the clones surviving proflavine treatment were phenotypically but not genetically resistant, and no strains were isolated which were resistant to proflavine but were not resistant to radiation.