Fluoroquinolone Compounds Research Articles

Spectroscopic studies on the lanthanide sensitized luminescence and chemiluminescence properties of fluoroquinolone with different structure

Lanthanide sensitized luminescence and chemiluminescence (CL) are of great importance because of the unique spectral properties, such as long lifetime, large Stokes shifts, and narrow emission bands characteristic to lanthanide ions (Ln 3+). With the fluoroquinolone (FQ) compounds including enoxacin (ENX), norfloxacin (NFLX), lomefloxacin (LMFX), fleroxacin (FLRX), ofloxacin (OFLX), rufloxacin (RFX), gatifloxacin (GFLX) and sparfloxacin (SPFX), the luminescence and CL properties of Tb 3+–FQ and Eu 3+–FQ complexes have been investigated in this contribution. Ce 4+–SO 3 2− in acidic conditions was taken as the CL system and sensitized CL intensities of Tb 3+–FQ and Eu 3+–FQ complexes were determined by flow-injection analysis. The luminescence and CL spectra of Tb 3+–FQ complexes show characteristic peaks of Tb 3+ at 490 nm, 545 nm, 585 nm and 620 nm. Complexes of Tb 3+–ENX, Tb 3+–NFLX, Tb 3+–LMFX and Tb 3+–FLRX display relatively strong emission intensity compared with Tb 3+–OFLX, Tb 3+–RFX, Tb 3+–GFLX and Tb 3+–SPFX. Quite weak peaks with unique characters of Eu 3+ at 590 nm and 617 nm appear in the luminescence and CL spectra of Eu 3+–ENX, but no notable sensitized luminescence and CL of Eu 3+ could be observed when Eu 3+ is added into other FQ. The distinct differences on emission intensity of Tb 3+–FQ and Eu 3+–FQ might originate from the different energy gap between the triplet levels of FQ and the excited levels of the Ln 3+. The different sensitized luminescence and CL signals among Tb 3+–FQ complexes could be attributed to different optical properties and substituents of these FQ compounds. The detailed mechanism involved in the luminescence and CL properties of Tb 3+–FQ and Eu 3+–FQ complexes has been investigated by analyzing the luminescence and CL spectra, quantum yields, and theoretical calculation results.

Polymorphism and Intramolecular Proton Transfer in Fluoroquinolone Compounds

Electronic absorption, luminescence, IR and Raman spectra of polymorphous forms of fluoroquinolones were investigated. Assignment of the band maxima due to π→π* and n→π* electronic transitions were done. The structural changes are responsible for the absorption band modifications. One-electron transitions in the long wavelength region, excitation wavelengths, oscillator strengths and involved molecular orbitals for the zwitter-ionic and cationic protonated forms for different fluoroquinolones were calculated with quantum-chemical and molecular dynamic methods. The electron density redistributions on the FQs separate fragments during the photoexcitation to the S(1)*-state were carry out by Mulliken calculations. It was shown that the degree of neutral and zwitter-ion FQs penetration through the bacterium membrane is different.

The role of water molecules in the interfragmental charge transfer of the protolytic forms of fluoroquinolones in the ground and excited states

Quantum-chemical analysis (TD-DFT/B3LYP/6-31G) of the influence of H-bonding in the donor-acceptor fluoroquinolone compounds with the water molecules on the interfragmentary charge transfer was carried out. The values of charge transfer between the molecular fragments in the transition from the ground into the singlet excited state were calculated. It was found that, depending on the protolytic form of a compound, the frontier molecular orbitals are localized on different fragments, which leads to the specificity of the formation of the electron density transfer channel. The influence of individual substituents in the quinolones on the localization of particular MOs is relatively insignificant.

Trends in soil sorption coefficients within common antimicrobial families

Sorption coefficients ( K d ) of fluoroquinolone, tetracycline, and sulfonamide antimicrobial compounds were measured for seven soils between pH 4.5 and 8.5 using batch sorption techniques. Soils were chosen to encompass a range of cation exchange capacity (CEC), iron and aluminum oxide and organic matter contents. For most soil-pH pairs, enrofloxacin, norfloxacin, and ciprofloxacin K d values were within a factor of 2 (0.3 log units) of each other. Lower enrofloxacin sorption than norfloxacin or ciprofloxacin sorption was observed at pH 8.5 for the two most aluminosilicate clay-rich soils, likely due to compound differences in acid dissociation constants, yielding greater anion species abundance for enrofloxacin. Tetracycline, oxytetracycline and chlortetracycline K d values also were within a factor of 2 for each soil-pH pair. Measured tetracycline and fluoroquinolone compound K d values could be estimated within a factor of 2 using published empirical multi-linear regression models. In contrast, sulfonamide K d values varied among compounds, as expected for sorbates that interact primarily with soil organic matter. Results of this research indicate that substituent groups have little effect on sorption interactions of compounds from the tetracycline and fluoroquinolone family that interact with soils primarily through cation exchange, surface complexation and cation bridging sorption mechanisms.

Fluoroquinolones lower constitutive H2AX and ATM phosphorylation in TK6 lymphoblastoid cells via modulation of the intracellular redox status

Accumulation of reactive oxygen species (ROS)-induced damage and mutations in the genomic DNA is considered the primary etiology of aging and age-related pathologies including cancer. Strategies aimed at slowing these conditions often involve protecting against oxidative DNA damage via modulation of the intracellular redox state. Recently, a biomarker of DNA double-strand breaks (DSBs), serine 139-phosphorylated histone H2AX (γH2AX), and its upstream mediator, activated PI-3-related kinase, ATM (ATMP1981), were shown to be constitutively expressed in cells and modulated by antioxidant treatment. Thus, both constitutive histone H2AX phosphorylation (CHP) and constitutive ATM activation (CAA) are thought to reflect a cell’s response to endogenous ROS-induced DSBs. In the present study, we investigated the effects of a battery of fluoroquinolone (FQ) compounds, namely ciprofloxacin, enrofloxacin, gatifloxacin, lomefloxacin and ofloxacin, on CHP and CAA in human TK6 lymphoblastoid cells. All FQs tested reduced CHP and CAA compared to controls following 6 and 24h treatment with CAA being more sensitive to their effects at both time points. In addition, intracellular ROS levels and mitochondrial activities were also lowered in FQ-treated cells at 6 and 24h. We presume that FQs mediate this effect via a combination of ROS-scavenging and mitochondrial suppression and therefore may protect against the onset or may slow the progression of numerous oxidative pathophysiological conditions.

Mutational paths towards increased fluoroquinolone resistance in Legionella pneumophila

Fluoroquinolone resistance has been poorly studied in Legionella pneumophila, an intracellular pathogen responsible for legionellosis. Our goal was to further characterize molecular mechanisms involved in fluoroquinolone resistance in this species. Eight independent lineages were founded from a common fluoroquinolone-susceptible L. pneumophila ancestor and propagated by serial passages in moxifloxacin-containing culture medium. We identified the substituted mutations that affected the DNA topoisomerase II-encoding genes, determined the order of substitution of the mutations leading to the stepwise MIC increases of moxifloxacin over evolutionary time and demonstrated their direct involvement in the resistance process. Adaptation occurred through parallel stepwise increases in the moxifloxacin MICs up to 512-fold the MIC for the parental strain. Mutations affected the topoisomerase II-encoding genes gyrA, parC and gyrB, reflecting a high degree of genetic parallelism across the independent lineages. During evolution, the T83I change in GyrA occurred first, followed by G78D or S80R in ParC and D87N in GyrA, or S464Y or D426N in GyrB. By constructing isogenic strains, we showed that the progressive increase in resistance was linked to a precise order of mutation substitution, but also to the co-existence of several subpopulations of bacteria bearing different mutations. Specific mutational trajectories were identified, strongly suggesting that intermolecular epistatic interactions between DNA topoisomerases underlie the mechanism of fluoroquinolone resistance in L. pneumophila. Our results suggest that L. pneumophila has strong potential to become resistant to fluoroquinolone compounds and warrant further investigation of resistance in clinical and environmental strains of this pathogen.

In vitro selection of fluoroquinolone resistance in Brucella melitensis

Moxifloxacin-resistant mutants of Brucella melitensis 16M [moxifloxacin minimum inhibitory concentration (MIC) = 1 mg/L] were selected in order to characterise fluoroquinolone resistance mechanisms in this species. Eight independent mutants were obtained, with moxifloxacin MICs of 16–32 mg/L. The mutants displayed variable cross-resistance levels to other fluoroquinolone compounds, but no increased resistance to aminoglycosides, tetracycline, rifampicin, macrolides or co-trimoxazole. Sequencing of type II topoisomerase-encoding genes ( gyrA, gyrB, parC and parE), which are natural targets for fluoroquinolones, revealed a gyrA mutation leading to the amino acid substitution Ala83Val ( Escherichia coli numbering system) in five mutants with a moxifloxacin MIC of 32 mg/L, whereas no mutation was found in the remaining three mutants with a MIC of 16 mg/L. Phenylalanine-arginine-β-naphthylamide dihydrochloride, an efflux pump inhibitor, reduced moxifloxacin MICs by a factor of two to eight in all resistant mutants. In B. melitensis, fluoroquinolone resistance may arise from gyrA mutation and efflux pump overexpression mechanisms.

HPLC of fluoroquinolone antibacterials using chiral stationary phase based on enantiomeric (3,3′‐diphenyl‐1,1′‐binaphthyl)‐20‐crown‐6

A residual silanol group-protecting chiral stationary phase (CSP) based on optically active (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 was successfully applied to the resolution of fluoroquinolone compounds including gemifloxacin mesylate. The chiral recognition ability of the residual silanol group-protecting CSP was generally greater than that of the residual silanol group-containing CSP. From these results, it was concluded that the simple protection of the residual silanol groups of the latter CSP with lipophilic n-octyl groups can improve its chiral recognition ability for the resolution of racemic fluoroquinolone compounds. The chromatographic resolution behaviors were investigated as a function of the content and type of organic and acidic modifiers and the ammonium acetate concentration in aqueous mobile phase and the column temperature. Especially, the addition of ammonium acetate to the mobile phase was found to be a quite effective means of reducing the enantiomer retentions without sacrificing the chiral recognition efficiency of the CSP.

A rapid microbial inhibition-based screening strategy for fluoroquinolone and quinolone residues in foods of animal origin

A rapid, high-throughput antimicrobial screening assay for the detection of fluoroquinolone and 4-quinolone residues in foods of animal origin has been developed in ampoule format. The assay employs a single Escherichia coli species sensitive to those Gram-negative inhibitiory antimicrobial compounds and is presented in a comparable format to the existing commercially available Premi ®Test and Delvotest ® ampoule-based microbial inhibition tests (DSM, Delft, The Netherlands). In the novel E. coli assay the microorganism, in vegetative state, is inoculated into a nutrient agar pellet containing a pH sensitive acid–base indicator dye. A simple extraction protocol that is selective for fluoroquinolone and quinolone compounds was developed to recover, cleanup and concentrate the target analyte(s) from a variety of tissue types and matrices prior to screening analysis. The method detected 16 target compounds at concentrations equal to or below the maximum residue limits (where applicable). The method has been validated using the prototype assay in accordance with the 2002/657/EC guidelines for the validation of qualitative screening assays. False positive and false negative responses rates for the procedure have been determined as less than 5%. The stability of a selection of representative target analytes has been demonstrated for a 20-week period under a variety of storage conditions both in tissue and in extract.

Zabofloxacin (DW-224a) activity against Neisseria gonorrhoeae including quinolone-resistant strains

Zabofloxacin, a new fluoroquinolone compound (DW-224a), was tested by reference agar dilution methods against 35 strains of multiresistant Neisseria gonorrhoeae. The potency of zabofloxacin (MIC 50, 0.016 μg/mL) was generally comparable with azithromycin but 8-fold superior to ciprofloxacin. This novel naphthyridine should be explored as an alternative therapy for quinolone-nonsusceptible gonorrhea and Chlamydia trachomatis infections.

Heterogeneity of susceptibility to fluoroquinolones in Bartonella isolates from Australia reveals a natural mutation in gyrA

Bartonella sp. are intracellular bacteria associated with an increasing number of clinical manifestations but with few published data on in vitro susceptibility testing of antibiotics. Our objective was to evaluate in vitro antibiotic susceptibilities of 20 new Bartonella isolates from animals in Australia. MICs were determined using Etest assay on Columbia agar supplemented with 5% horse blood. The presence of mutations in the quinolone-resistance-determining region (QRDR) of gyrA was searched for after PCR amplification and DNA sequencing using specific oligonucleotide primers. Bartonella isolates from Australia were susceptible to rifampicin, tetracyclines, beta-lactam and macrolide compounds but were resistant to vancomycin. We found heterogeneity of susceptibility for fluoroquinolones with ciprofloxacin being more effective (MICs from 0.06 to 0.5 mg/L) than ofloxacin (MICs from 0.5 to 4 mg/L). This heterogeneity was linked to a natural mutation Ser-83-->Ala (Escherichia coli numbering) in the QRDR. Surprisingly, this mutation was also present in the QRDR of Bartonella henselae, Bartonella quintana and Bartonella bacilliformis. Etest is a sensitive and reliable assay for evaluation of antibiotic susceptibility in the genus Bartonella. The higher sensitivity of this method allowed us to detect heterogeneity of susceptibility among fluoroquinolones that was associated with natural mutation in the QRDR of the DNA gyrase. Because a high level of resistance to fluoroquinolones due to a second mutation may be obtained easily in vitro, we believe that fluoroquinolone compounds should be avoided for the treatment of any Bartonella-related diseases.

Analysis and Sorption Behavior of Fluoroquinolones in Solid Matrices

A simple analytical method for the quantitative analysis of fluoroquinolone group antibiotics, enrofloxacin (ENR) and ciprofloxacin (CIP) in soil was developed based on the mechanical extraction with vortex and ultrasonication and solid phase extraction followed by high pressure liquid chromatography-fluorescence detection (HPLC-FLD). Type of extraction solvents and number of extraction cycles were optimized during the method development. The most efficient extraction solvent was found as phosphate buffer at pH 3 in combination with 50% of organic modifier acetonitrile with the extraction cycle of four. Overall method was applied on three different types of soils, namely, sandy, loamy sand and sandy loam and recovery rates ranged between 71–100% for ENR and 61–89% for CIP depending on the portion of organic and clay content in soils. The analytical method was also used for the estimation of fluoroquinolone concentrations in manure amended agricultural soils sampled from the different parts of Turkey and enrofloxacin was detected in the concentration range of 0.013–0.204 mg/kg. In addition, sorption of fluoroquinolone antibiotics on all types of soils was investigated and the highest distribution coefficients (Kd and Kf) of fluoroquinolone compounds were obtained for loamy sand (Kd = 1.29 l/g and Kf = 0.66 for CIP; Kd = 0.97 l/g and Kf = 0.56 for ENR) with the highest organic carbon.

Trovafloxacin-Induced Gene Expression Changes in Liver-Derived in Vitro Systems: Comparison of Primary Human Hepatocytes to HepG2 Cells

Primary human hepatocytes (PHH) are a main instrument in drug metabolism research and in the prediction of drug-induced phase I/II enzyme induction in humans. The HepG2 liver-derived cell line is commonly used as a surrogate for human hepatocytes, but its use in absorption, distribution, metabolism, and excretion and toxicity studies can be limited because of lowered basal levels of metabolizing enzymes. Despite the widespread use of HepG2 cells, a comparison of their transcriptomes with those of PHH has not been well characterized. In this study, microarray analysis was conducted to ascertain the differences and similarities in mRNA expression between HepG2 cells and human hepatocytes before and after exposure to a panel of fluoroquinolone compounds. Comparison of the naive HepG2 cell and PHH transcriptomes revealed a substantial number of basal gene expression differences. When HepG2 cells were dosed with a series of fluoroquinolones, trovafloxacin (TVX), which has been associated with human idiosyncratic hepatotoxicity, induced substantially more gene expression changes than the other quinolones, similar to previous observations with PHH. Although TVX-treatment resulted in many gene expression differences between HepG2 cells and PHH, there were also a number of TVX-induced commonalities, including genes involved in RNA processing and mitochondrial function. Taken together, these results provide insight for interpretation of results from drug metabolism and toxicity studies conducted with HepG2 cells in lieu of PHH and could provide further insight into the mechanistic evaluation of TVX-induced hepatotoxicity.

MODEL QSAR SENYAWA FLUOROKUINOLON BARU SEBAGAI ZAT ANTIBAKTERI Salmonella thypimurium Eva Vaulina, Ponco Iswanto

Modelling of novel Fluoroquinolone derivates as antibacterial compund of Salmonella thypimurium was conducted. The research was done as an initial step in discovering some new Fluoroquinolone compounds which have higher activity to Salmonella thypimurium. There are 16 compunds that use as the material of the research and they already have antibacterial activity data that expressed in Minimal Inhibitory Concentration (MIC, mg/mL). Calculation was performed by semiempirical AM1 method. The QSAR model was determined by multilinear regression analysis, with Log MIC as dependent variable and the independent variables are atomic net charges of C5 (qC5) and C7 (qC7), dipole moment (m), polarizability (a), n-octanol-water coefficien partition (Log P), molecular weight (Mw), and surface area of van der Waals (AvdW). The relationship between Log MIC and the descriptors which performed by statistical analysis is:(Log MIC) = -2.119 + 34.541(qC5) – 19.748(qC7) – 0.919polar + 1.170logP + 0.111(Mw) – 0.003(Avdw), with n =16, r = 0.907, r2 = 0.822, SD = 0.288, F calc = 6.938, F table = 3.374 , F calc/F table = 2.056 and PRESS = 0.749. The research can obtain the new coumpounds that modified from compound number 16 (etil fluoroquinolone, MIC prediction = 0.0354 mg/mL), (etil fluoroquinlone fosfate, 2.84. 10-19mg/mL), and (isopropyl fluoroquinlone, 0.1085 mg/mL), and compound number 2 (m-nitro fluoroquinolone sulfonat, 1.32. 10-11mg/mL). This results can be suggested to synthesis step.

Direct chiral separation of caderofloxacin enantiomers by HPLC using a glycoprotein column

The enantiomers of caderoflxacin (CS-940), the new antibacterial fluoroquinolone compound, were separated on the commercially available α-acid glycoprotein-coated chiral stationary phase (Chiral-AGP) using the mobile phase of IPA: 0.15 M NaH2PO4 + Et3N (pH 7.9) = 3: 97 at 0.8 mL/min with UV detection at 282 nm. The chromatographic behavior of caderofloxacin enantiomers was investigated by varying the mobile phase conditions. The chiral assay method was validated and used to determination of (R)-Caderofloxacin in (S)-Caderofloxacin raw material samples.

Chiral separation of four fluoroquinolone compounds using capillary electrophoresis with hydroxypropyl-β-cyclodextrin as chiral selector

A capillary zone electrophoresis (CZE) investigation on the enantiomeric separation of lomefloxacin, gatifloxacin, pazufloxacin and ofloxacin was undertaken. Resolution of the enantiomers was achieved using hydroxypropyl-β-cyclodextrin (HP-β-CD) as the chiral selector. Parameters influencing separation include cyclodextrin concentration, separational potential, pH and organic additive are discussed. A buffer consisting of 70 mM phosphate and 40 mM HP-β-CD at pH 3.96 was found to be highly efficient for the separation of lomefloxacin, at pH 3.90 for gatifloxacin, at pH 5.04 for pazufloxacin and at pH 2.16 for ofloxacin. To the best of our knowledge, this is the first report on the enantiomeric resolution of lomefloxacin and gatifloxacin applying CE.

Relation between induction of the mar operon and cyclohexane tolerance and reduction in fluoroquinolone susceptibility in Salmonella spp.

The relationship between cyclohexane tolerance and induction of the mar operon and a decrease in susceptibility to ciprofloxacin and moxifloxacin in isolates of Salmonella spp. from food and clinical isolates of Salmonella spp. was studied. We studied the influence of the mar operon using an inductor (acetylsalicylic acid) and we also studied the cyclohexane resistance. Induction was seen to produce an increase in the minimum inhibitory concentration (MIC) of these quinolones, which suggested that there was overexpression of the AcrAB type active efflux systems due to induction of the mar operon. Cyclohexane susceptibility was not shown to be a very sensitive method for studying this process, as only 3% (5/176) of the clinical isolates studied were cyclohexane-resistant; most of these belonged to the Hadar serotype. This study confirmed the participation of active efflux systems in the decrease in fluoroquinolone susceptibility in Salmonella spp. Furthermore, the study has indicated that these mechanisms (i.e., active efflux systems) are present in strains that are susceptible to the fluoroquinolone compounds, so their stimulation may be one of the mechanisms involved in the reduction in fluoroquinolone susceptibility. This suggests that the exposure of Salmonella spp. to antibiotics should be limited in order to prevent these active efflux systems from being activated. Consequently, the use of fluoroquinolones, both in the treatment of humans and in veterinary practice, should be controlled and rationalized in an attempt to curb the increase in the number of strains that are resistant to these compounds.

In vitro activities of 11 fluoroquinolones against 816 non-typhoidal strains of Salmonella enterica isolated from Finnish patients with special reference to reduced ciprofloxacin susceptibility

BackgroundThe number of Salmonella strains with reduced susceptibility to fluoroquinolones has increased during recent years in many countries, threatening the value of this antimicrobial group in the treatment of severe salmonella infections.MethodsWe analyzed the in vitro activities of ciprofloxacin and 10 additional fluoroquinolones against 816 Salmonella strains collected from Finnish patients between 1995 and 2003. Special attention was focused on the efficacy of newer fluoroquinolones against the Salmonella strains with reduced ciprofloxacin susceptibility.ResultsThe isolates represented 119 different serotypes. Of all 816 Salmonella strains, 3 (0.4%) were resistant to ciprofloxacin (MIC ≥ 4 μg/ml), 232 (28.4%) showed reduced susceptibility to ciprofloxacin (MIC ≥ 0.125 – 2 μg/ml), and 581 (71.2%) were ciprofloxacin-susceptible. The MIC50 and MIC90 values of ciprofloxacin for these strains were 0.032 and 0.25 μg/ml, respectively, being lower than those of the other fluoroquinolone compounds presently on market in Finland (ofloxacin, norfloxacin, levofloxacin, and moxifloxacin). For two newer quinolones, clinafloxacin and sitafloxacin, the MIC50 and MIC90 values were lowest, both 0.016 and 0.064 μg/ml, respectively. Moreover, clinafloxacin and sitafloxacin exhibited the lowest MIC50 and MIC90 values, 0.064 and 0.125 μg/ml, against the 235 Salmonella strains with reduced susceptibility and strains fully resistant to ciprofloxacin.ConclusionAmong the registered fluoroquinolones in Finland, ciprofloxacin still appears to be the most effective drug for the treatment salmonella infections. Among the newer preparations, both clinafloxacin and sitafloxacin are promising based on in vitro studies, especially for strains showing reduced ciprofloxacin susceptibility. Their efficacy, however, has not been demonstrated in clinical investigations.

Measurement of the antibiotic susceptibility of Coxiella burnetii using real time PCR

The objective of this study was to determine MICs of antibiotics for two reference strains of Coxiella burnetii using real time quantitative PCR. The method was very sensitive and specific and allowed the evaluation of the doubling time of Nine Mile and Q212 strains: 37 and 15 h, respectively. Dose response curves of antibiotics were used to determine MICs. Those of doxycycline, fluoroquinolone compounds and rifampicin were in the range 1–4 mg/l. Telithromycin was the most effective macrolide compound with MICs of 1–2 mg/l. The results confirmed previous reports on the accuracy of this new method for the determination of the antibiotic susceptibility of C. burnetii and could be used for the screening of new drugs.

In vitro and in vivo antipseudomonal activity, acute toxicity, and mode of action of a newly synthesized fluoroquinolonyl ampicillin derivative

Compounds N-(6,7-difluoroquinolonyl)-ampicillin (AU-1) and N-(6-fluoroquinolonyl)-ampicillin (FQ-1), synthesized by coupling of the carboxyl group of 6,7-difluoroquinolone (FP-3) and 6-fluoroquinolone (FP4), respectively, with the α-amino-group of ampicillin side chain, exhibit antipseudomonal activity similar to and lower acute toxicity than that of norfloxacin, whereas neither ampicillin nor the fluoroquinolone moieties, compound FP-3 or FP4, alone have such activity. Also, AU-1 and FQ-1 are active against tested clinical isolates of Pseudomonas aeruginosa that are highly resistant to norfloxacin, gentamicin, or both. The therapeutic efficacies of FQ-1 and norfloxacin were assessed and compared in neutropenic mice infected with a 90% lethal dose of P aeruginosa. Mice intraperitoneally administered FQ-1 (10 mg/kg) 4, 8, 24, and 48 hours after infection had survival rates as high as 80%, comparable to those of mice treated with norfloxacin at the same dosage and dosing schedule. The study of protoplast formation revealed that FQ-1 did not inhibit cell-wall biosynthesis but did induce cell filamentation of Bacillus subtilis at a level close to its minimal inhibition concentration. Both AU-1 and FQ-1 were able to intercalate into the double-stranded DNA. However, that FQ-1 lost such activity after it was treated with penicillinase suggests that the lactam-ring structure in ampicillin moiety of FQ-1 was hydrolyzed by penicillinase and that the hydrolyzed structure of FQ-1 does not own DNA-intercalation activity.