Induction of lambda prophage by furazolidone

Role of Turmeric in Ultraviolet Induced Genotoxicity in a Bacterial System

Turmeric extracts contain more than one bioactive component, which have different properties when used to modulate ultraviolet induced genotoxicity. These differences were found depending on the nature and extent of the damage to the bacterial DNA, which indicates the existence of a natural switching process in sensing the damage.

Transcriptional profile induced by furazolidone treatment of Shigella flexneri

Shigella flexneri is a facultative intracellular pathogen responsible for endemic shigellosis especially in developing countries. Furazolidone, a nitrofuran derivative, is very effective against the infection with S. flexneri. To examine potential effects of furazolidone on this germ, a whole-genome DNA microarray was constructed and transcriptional profiles of the responses to furazolidone were determined. The expressing data revealed adaptive responses of S. flexneri to oxidative stress induced by furazolidone treatment. Iron metabolism was found to be disturbed by furazolidone through derepression of the iron uptake regulon. In addition, energy metabolism, amino acid metabolism, cofactors metabolism, and DNA repair system were also affected by the drug. These data establish a potential for furazolidone to enhance free radical reactions through reductive activation by oxygen-sensitive nitroreductase. Moreover, we provide evidence that furazolidone is able to cause metabolic dysfunction, which cannot always be attributed to oxidative stress, and interactions between reductive metabolites of furazolidone and S. flexneri should be considered.

In vitro activity of nitrofuran derivatives on growth and morphology of Salmonella enterica serotype Enteritidis

AIMS

To evaluate the effect of nitrofuran derivatives furazolidone (Fz) and nitrofurantoin (Nf) on Salmonella enterica serovar Enteritidis PT4 in vitro, with regard to cell growth, morphology and ultrastructure.

METHODS AND RESULTS

The effects of Fz on the growth rates of Fz resistant (FzR) and sensitive (FzS) strains were assessed by viable counts. Over 24 h incubation, concentrations of <1 microg ml(-1) of Fz were bacteriostatic to the FzS strain. The FzR strain tolerated concentrations up to 16 microg ml(-1) before cell numbers diminished over the same time period. The effect on the growth rate of the FzS strain after 1 h exposure to supra-inhibitory concentrations of Fz, gave a maximum response at 32X minimum inhibitory concentration (MIC) of 4.5 h. Effects on the ultrastructure of bacterial cells by scanning electron and transmission microscopy, and DNA-specific staining with DAPI of the FzS strain exposed to nitrofurans were studied. Abnormalities such as extensive filamentation with sparse, sporadic nucleotide distribution and evidence of extrusions in the cell envelope in the form of blebs were evident.

CONCLUSIONS

Nitrofurans exert their bactericidal effect on Salmonella by inducing extensive structural alteration after exposure at sub- or suprainhibitory concentrations, involving inhibition of cell division because of the activated drug causing an intercalating type of binding in DNA.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results demonstrate the in vitro activity of the nitrofuran derivatives, furazolidone and nitrofurantoin on Salmonella, defining the pharmacodynamics and physical nature of their action as therapeutic agents.

Studies on the genotoxicity of endosulfan in bacterial systems

Endosulfan, an organochlorine pesticide, was subjected to the differential sensitivity assay in repair-deficient and repair-proficient strains of Escherichia coli K12, prophage lambda induction assay in WP2s (lambda) and mutation induction in E. coli K12. The induction of umu gene expression with endosulfan was studied also in Salmonella typhimurium TA1535/pSK1002 cells. The differential sensitivity assay revealed that the recA 13 strain was the most sensitive. Endosulfan induced prophage lambda in E. coli and umu gene expression in S. typhimurium cells; however, the extent of the effects were low. Endosulfan also induced a dose-dependent increase in forward mutations in E. coli K12 cells from ampicillin sensitivity to ampicillin resistance. Our studies indicate the genotoxic potential of endosulfan and the role of the recA gene in the repair of endosulfan-induced DNA damage.

Inter-strand cross-linking of Vibrio cholerae DNA induced by furazolidone: a quantitative assay by four simple methods

Four simple methods, i.e., (i) UV absorption spectrophotometry, (ii) hydroxyapatite chromatography, (iii) fluorescence analysis of ethidium bromide bound to DNA and (iv) assay of S1 endonuclease action, were used in parallel for the estimation of furazolidone-induced inter-strand cross-links in Vibrio cholerae DNA. The data produced by the four methods were in reasonable agreement with each other and provided similar linear dose-response relations, the correlation (between dose and response) coefficient being in any case numerically greater than 0.98. When the data obtained by four independent methods were plotted in a single graph, the resulting dose-response relation could be described by the equation log NR = 1.41 - 0.54 log D, where NR is the % non-reversible DNA remaining in the cells treated by furazolidone at dose D micrograms/ml x h. The correlation coefficient in this plot was -0.98 and significant to a level better than 0.1%. This study thus brings out that any one of these four methods can be used with reasonable confidence for the diagnosis and assay of inter-strand cross-links in DNA.

Resistance to the nitroheterocyclic drugs

The nitroheterocyclic drugs have been available since the early 1960's for the treatment of anaerobic protozoa. The application of these drugs has widened since then and they are presently used to treat anaerobic pathogenic bacteria and protozoa. The activity of the nitroheterocyclic drugs depends on the all-important nitro group attached to the imidazole or furan ring. Although the nitro radicals, generated by reduction of the parent drugs, are similar for both families of nitroheterocyclics, the nitroimidazoles and the nitrofurans, the electron potential of each is different and thus the mechanism of action depends on different pathways. The nitroimidazoles depend on reduction by ferredoxin or flavodoxin. The nitrofurans require nitroreductase activity, but the natural substrate of these enzymes has not been identified. Increased use of nitroheterocyclic drugs, in response to drug resistance to other commonly used antibiotics, has in turn resulted in drug resistance to a number of nitroheterocyclic drugs. Bacteroides strains and other bacteria, including Helicobacter, have developed resistance. Among the protozoa, Trichomonas has developed resistance to metronidazole via a number of mechanisms, especially a decrease in drug reduction, as a result of alterations in the electron transport pathways. Resistance to both types of nitroheterocyclic drugs has been reported in Giardia. Although resistance to these drugs is not widespread, their increased use world-wide as a prophylaxis and in chemotherapy will inevitably result in increased resistance in organisms commonly found in asymptomatic infections, including Trichomonas, Giardia and Entamoeba. However, the variety of substitutions which can be attached to the ring structures has led to a great variety of drugs being synthesised, some of which are many-fold more active than the commonly prescribed nitroheterocyclics. With careful administration of currently available drugs and continued interest in synthesising more active compounds, we can optimistically expect to have useful nitroheterocyclic drugs available for some time.

On the induction of umu gene expression in Salmonella typhimurium strain TA1535/pSK1002 by some nitrofurans

Several nitrofurans were found to induce umu gene expression in Salmonella typhimurium TA1535/pSK1002 as defined on the basis of at least a 2-fold increase of beta-galactosidase activity over the background level. beta-Galactosidase activity increased with increasing concentrations of the chemical, attained a maximum at a concentration which was different for different nitrofurans used, and then gradually decreased with a further increase of the nitrofuran concentration. The umu gene expression test revealed that the genotoxic activity was highest for furazolidone and lowest for 5-nitro-2-furaldehyde.

In-vitro interaction between nitrofurantoin and Vibrio cholerae DNA

In-vitro interaction of nitrofurantoin with V. cholerae DNA resulted in a quenching and red spectral shift of the drug absorption pattern. Scatchard analysis revealed that the drug binding involved more than one processes and that the strongest mode of binding was characterised by an association constant (k) of 5.04 x 10(6) M-1 and the number of binding sites per nucleotide (n) of 0.015. Based on viscosity measurements, the mode of drug binding to DNA appeared to be through intercalation, the helix unwinding angle of supercoiled plasmid pBR322 DNA being 10 degrees. Nitrofurantoin binding to DNA resulted in an elevation of the thermal melting temperature (Tm) of DNA by 6 degrees C and inhibition of the action of DNase on DNA.

DNA damage and prophage induction and toxicity of nitrofurantoin in Escherichia coli and Vibrio cholerae cells

Repair-deficient and repair-proficient strains of E. coli K12 were sensitive to nitrofurantoin treatment to varying degrees with the double mutant strain (uvrA 6, recA 13) being most sensitive. Ultraviolet absorption data and thermal chromatography through a hydroxyapatite column revealed that nitrofurantoin treatment of V. cholerae strain OGAWA 154 produced a maximal amount of 55% reversibly bihelical DNA at a nitrofurantoin dose of 120 micrograms/ml/h, which indicated the formation of inter-strand cross-links in DNA. Nitrofurantoin also produced prophage-lambda induction in E. coli K12 strain GY 5027: envA, uvrB, ampA 1, strA (lambda), in a dose-dependent manner, the maximum induction being highly significant (P less than 0.001). Previously published mutation data coupled with the prophage induction data presented here suggest that the genotoxic properties of nitrofurantoin are mediated through the SOS pathway.

Furazolidone-induced interstrand cross-links in Vibrio cholerae DNA. Study of conformational change by circular dichroism

Vibrio cholerae DNA bearing furazolidone-induced interstand cross-links show a change in the characteristic circular dichroism spectra of the DNA itself in dilute buffer. The change in c.d. spectra was characterized by a shift of the positive band around 272 nm to lower wavelength and a loss of ellipticity of the negative band around 242 nm, and is similar to that exhibited by mitomycin linked Vibrio cholerae DNA under identical conditions and is suggestive of a conformational change of DNA bearing such cross-links. Both furazolidone-induced and mitomycin-induced cross-linking of Vibrio cholerae DNA inhibited the salt-induced conformation change, i.e. increase in winding angle of DNA, the percentage inhibition being greater for mitomycin-linked DNA.

An adaptive response of Vibrio cholerae strain OGAWA 154 to furazolidone

Since furazolidone is an antimicrobial drug, any possibility of its evoking an adaptive response appears to be very important. This response was studied in Vibrio cholerae cells as a model system. In order to determine this response, a dose-response relation of these cells to furazolidone and the kinetics of inactivation of the drug were studied. The study of the adaptive response of these cells to furazolidone reveals that cells treated with a low concentration of furazolidone for a particular period were 100% more resistant to the lethal effects of a subsequent challenging dose than control cultures. Variation of the challenging dose level showed better survival of adapted cells than control cells. A time-dependent response study reveals a maximum response at 15-30 min, and a gradual fall thereafter.

DNA damage by 5-nitro-2-furylacrylic acid, a nitrofuran derivative

5-Nitro-2-furylacrylic acid (5-NFA) caused dose dependent inhibition of growth of Escherichia coli K-12 strain AB 2480 (uvr-, rec-), the 37% (D37) and 10% (D10) survival doses being 1.0 microgram/ml.h and 1.75 micrograms/ml.h, respectively. Although much higher doses of drug were required to achieve comparable inhibition of growth of E. coli strain 1157 (repair proficient), significant filamentation of these cells was produced by treatment with 1.0 microgram/ml 5-NFA for 4 hr. Ultraviolet absorption data and thermal chromatography through hydroxyapatite (HAP) column revealed that 5-NFA treatment of E. coli strain AB 2480 produced more than 80% of DNA reversibly bihelical due to the formation of interstrand cross-links and the initial part of the reaction obeyed a first order relation. 5-NFA also produced dose-dependent increase of prophage induction in E. coli strain GY 5027: envA, uvrB, ampA1, strA (lambda). The implications of the action of 5-NFA on DNA in relation to the induction of 'SOS' functions and carcinogenesis were discussed.