DNA Gyrase Subunit Research Articles

Synthesis and molecular docking study of pyrazole clubbed oxazole as antibacterial agents

We have developed a simple synthetic protocol for the preparation of novel 3-(3-(4-fluorophenyl)-1-phenyl-1H-pyrazol-4-yl)-5-arylisoxazoles. The structure of synthesized compounds was elucidated by spectral techniques like FT-IR, 1H-NMR, 13C-NMR, and mass. The novel bioactive compounds 3a-t were evaluated for in vitro antibacterial activity on several bacterial species. Compounds 3c (–4–NO2), 3o (–4–F), and 3r (–3,4–Cl2) exhibited good in vitro antibacterial activity. Furthermore, molecular docking on DNA gyrase subunit b could shed some light on the mechanism of action which can serve as a guide for lead optimization.

Exploration of the Neisseria Resistome Reveals Resistance Mechanisms in Commensals That May Be Acquired by N. gonorrhoeae through Horizontal Gene Transfer.

Nonpathogenic Neisseria transfer mutations encoding antibiotic resistance to their pathogenic relative Neisseria gonorrhoeae. However, the resistance genotypes and subsequent phenotypes of nonpathogens within the genus have been described infrequently. Here, we characterize the minimum inhibitory concentrations (MICs) of a panel of Neisseria (n = 26)—including several commensal species—to a suite of diverse antibiotics. We furthermore use whole genome sequencing and the Comprehensive Antibiotic Resistance Database Resistance Gene Identifier (RGI) platform to predict putative resistance-encoding mutations. Resistant isolates to all tested antimicrobials including penicillin (n = 5/26), ceftriaxone (n = 2/26), cefixime (n = 3/26), tetracycline (n = 10/26), azithromycin (n = 11/26), and ciprofloxacin (n = 4/26) were found. In total, 63 distinct mutations were predicted by RGI to be involved in resistance. The presence of several mutations had clear associations with increased MIC such as DNA gyrase subunit A (gyrA) (S91F) and ciprofloxacin, tetracycline resistance protein (tetM) and 30S ribosomal protein S10 (rpsJ) (V57M) and tetracycline, and TEM-type β-lactamases and penicillin. However, mutations with strong associations to macrolide and cephalosporin resistance were not conclusive. This work serves as an initial exploration into the resistance-encoding mutations harbored by nonpathogenic Neisseria, which will ultimately aid in prospective surveillance for novel resistance mechanisms that may be rapidly acquired by N. gonorrhoeae.

Synthesis, Biological Evaluation and Molecular Docking Study of Pyrazole, Pyrazoline Clubbed Pyridine as Potential Antimicrobial Agents

Introduction: In continuation of our efforts to find new antimicrobials, herein we report the synthesis of various pyrazole, pyrazoline, and pyridine based novel bioactive heterocycles (3a-t). Methods: Newly synthesized compounds were analysed for their antimicrobial activity. Compounds 3c, 3h, 3i, 3k, 3n, and 3q showed significant antimicrobial activity. Results: Molecular docking study for the most active analogues against DNA gyrase subunit b (PDB ID: 1KZN) corroborated well with the observed antimicrobial potency exhibiting significant binding affinity. Conclusion: Interpretation of the chemical structures reported in this paper was based on IR, 1H NMR, 13C NMR, and mass spectral data.

Inhibition of indole production increases the activity of quinolone antibiotics against E. coli persisters

Persisters are a sub-population of genetically sensitive bacteria that survive antibiotic treatment by entering a dormant state. The emergence of persisters from dormancy after antibiotic withdrawal leads to recurrent infection. Indole is an aromatic molecule with diverse signalling roles, including a role in persister formation. Here we demonstrate that indole stimulates the formation of Escherichia coli persisters against quinolone antibiotics which target the GyrA subunit of DNA gyrase. However, indole has no effect on the formation of E. coli persisters against an aminocoumarin, novobiocin, which targets the GyrB subunit of DNA gyrase. Two modes of indole signalling have been described: persistent and pulse. The latter refers to the brief but intense elevation of intracellular indole during stationary phase entry. We show that the stimulation of quinolone persisters is due to indole pulse, rather than persistent, signalling. In silico docking of indole on DNA gyrase predicts that indole docks perfectly to the ATP binding site of the GyrB subunit. We propose that the inhibition of indole production offers a potential route to enhance the activity of quinolones against E. coli persisters.

The Role of Some Transcription Factors in Expression of GyrA and GyrB Following Exposure to Ciprofloxacin

Background: GyrA and gyrB genes encode DNA gyrase subunits. This enzyme regulates DNA supercoiling. Inhibitors of this enzyme, such as ciprofloxacin, may change the level of supercoiling and the expression level of genes, including gyrA and gyrB. Objectives: The aims of this research were first to select some transcription factors, which regulate the expression of gyrA and gyrB. Secondly, the effect of these transcription factors was investigated on the expression of these genes in Escherichia coli mutants with different levels of resistance to ciprofloxacin in the presence and absence of these transcription factors. Methods: For this purpose, the online software called Promoter Analyzer in Virtual Footprint version 3 was used to find and select some transcription factors. The relative expression of genes was determined by quantitative real-time polymerase chain reaction (qRT-PCR). Results: Theoretical results showed that CspA, FhlA, and SoxS transcription factors (with a score of match higher than 6), could be selected for further analysis. The expression of gyrA and gyrB genes remained unchanged in the presence and absence of CspA and FhlA transcription factors following exposure to the low amount of ciprofloxacin. However, SoxS transcription activator might have indirect effects on the expression of these genes, as soxS gene was overexpressed following treatment with a higher amount of ciprofloxacin. Conclusions: It is concluded that overexpression of gyrA and gyrB genes is not dependent on CspA and FhlA transcription factors, but may be dependent indirectly on regulatory proteins involved in oxidative stress following exposure to ciprofloxacin.

Specific gyrA Gene Mutations Correlate with High Prevalence of Discordant Levofloxacin Resistance in Mycobacterium tuberculosis Isolates from Beijing, China

Although rapid, highly sensitive molecular diagnostics tests are useful for diagnosing fluoroquinolone-resistant tuberculosis (TB), results of molecular testing versus conventional sequential phenotypic drug susceptibility testing (pDST) are frequently discordant. This article determined the discordance rate of levofloxacin (LFX) resistance results, obtained via MeltPro TB molecular testing, versus pDST of clinical TB isolates collected in Beijing, China, between January and December 2018. Isolates with discordant results were further subjected to LFX minimal inhibitory concentration (MIC) determinations and DNA sequence analysis to explore causes of discordance. Of 571 total TB cases, 126 (22.1%) were identified as LFX resistant using the MeltPro TB assay. However, 34 of these 126 LFX-resistant isolates yielded LFX-susceptible test results using pDST, for an overall discordance rate of 27.0%. LFX MICs mainly clustered around the critical LFX concentration, with 7 (21.2%) and 13 (39.4%) of isolates exhibiting MICs of 2.0 and 4.0 mg/L, respectively. The most prevalent LFX resistance mutations associated with discordant results were involved in DNA gyrase subunit A amino acid substitutions Ala90Val (13, 39.4%) and Asp94Ala (11, 33.3%). Notably, more than one-quarter of isolates deemed LFX resistant via the MeltPro assay were scored as LFX susceptible on the basis of pDST results. Ultimately, highly discordant LFX-resistance test results were associated with specific gyrA mutations in isolates with MICs approaching the critical LFX concentration.

Synthesis, Antimicrobial, Antioxidant and Molecular Docking Studies on Novel 6-Methoxybenzothiazole-piperazine Derivatives with Propanamide Chain.

Infectious diseases are a major threat in the developing world and the discovery of novel antimicrobial agents remains to be crucial due to acquired resistance by the microorganisms. Additionally, various diseases can be prevented with antioxidant agents as they can eliminate the harmful effects of reactive oxygen species. In this study, it was aimed to synthesize novel compounds bearing N-(6- methoxybenzothiazol-2-yl)-3-(4-substitued piperazinyl)propanamide backbone that had antimicrobial and antioxidant activities. Mechanisms of activity were aimed to be revealed by docking studies. Antimicrobial activities were tested by agar-based disc diffusion assay, and antioxidant activities were determined by CUPRAC assay. In agar-based disc diffusion assay, the most active compounds were 2b and 2e against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Candida albicans. Compounds 2e and 2j showed promising antioxidant activity in CUPRAC assay. Docking studies were performed to optimize the interactions of compounds with DNA gyrase subunit B of S. aureus. Under the light of docking studies, a new compound with potential GyrB inhibition was designed. Antioxidant activity was also supported by docking studies on superoxide dismutase 1 enzyme in which interactions with key residues were observed. Ten novel benzothiazole-piperazine derivatives were synthesized and their antimicrobial and antioxidant activities were evaluated. Superoxide dismutase 1 enzyme was suggested to be a possible target for the antioxidant activity of the series.

Antimicrobial evaluation and docking study of some new substituted benzimidazole-2yl derivatives.

Benzimidazoles incorporated biologically active heterocycles such as quinoline, triazine-3-thione, thiazole and thiadiazole, were synthesized utilizing 2-acetylbenzimidazole as a building block. The structures of the newly synthesized benzimidazoles were assured by their spectral data (IR, 1H NMR, 13C- NMR and MS spectra). Most of the synthesized candidates were screened for their in vitro antimicrobial activity against Staphylococcus aureus, Escherichia coli, Bacillus pumilus and antifungal activity against (Saccharomyces cerevisiae). As a result, 2-(2-(1-(1H-benzo[d]imidazol-2-yl)ethylidene)hydrazineyl)-5-(furan-2-yl)-1,3,4-thiadiazole (14) had the most potent inhibitory activity against all tested bacteria with no antifungal inhibition. Furthermore, to gain insight into the mode of action of the synthesized compounds as antibacterial agents, docking studies were performed for the synthesized compounds in order to evaluate their activity as anti-bacterial agents. Virtual screening of the most promising compounds was performed against two bacterial proteins (DNA gyrase subunit B, and penicillin binding protein 1a) that are known targets for some antibiotics.

Fluoroquinolone resistance and mutational profile of gyrA in pulmonary MDR tuberculosis patients

BackgroundFluoroquinolones (FQs) are potential drugs that inhibit DNA synthesis and are used in the treatment of multidrug-resistant tuberculosis (TB) and short-term anti-TB regimens. In recent years, a high proportion of FQ resistance has been observed in Mycobacterium tuberculosis isolates. The development of FQ resistance in multidrug-resistant TB negatively impacts patient treatment outcome and is a serious threat to control of TB.MethodsThe study included a total of 562 samples from patients with pulmonary TB that had been on anti-tuberculosis therapy. MTBDRsl assays were performed for the molecular detection of mutations. Sequence analysis was performed for the characterization and mutational profiling of FQ-resistant isolates.ResultsFQ resistance was observed in 104 samples (18.5%), most of which were previously treated and treatment failure cases. A total of 102 isolates had mutations in DNA gyrase subunit A (gyrA), while mutations in gyrB were observed in only two isolates. Mutational analysis revealed that the mutations mostly alter codons 94 (replacing aspartic acid with glycine, D94G) and 90 (replacing alanine with valine, A90V). In MDR and treatment failure cases, resistance to FQs was most commonly associated with the D94G mutation. In contract, a high proportion of A90V mutations were observed in isolates that were newly diagnosed.ConclusionThe findings suggest that genotypic assays for FQ resistance should be carried out at the time of initial diagnosis, before starting treatment, in order to rule out mutations that impact the potential use of FQs in treatment and to control drug resistance.

Antimicrobial Pyridazines: Synthesis, Characterization, Cytotoxicity, Substrate Promiscuity, and Molecular Docking.

A facile and convenient synthesis of new pyridazines suitable for use as antimicrobial agents was reported. The hydrazide intermediate was coupled with various benzaldehydes and/or acetophenones and cyclized instantaneously to afford target pyridazine derivatives. The structures of new pyridazines were confirmed by IR, 1 H- and 13 C-NMR, elemental analysis in addition to representative LC/MS. Antimicrobial activity was screened against 10 bacterial and fungal strains. The new pyridazines showed strong to very strong antibacterial activity against Gram-negative (GNB) bacteria, while none of them showed significant antifungal activity at the same concentration range. Chloro derivatives exhibited the highest antibacterial activity with MICs (0.892-3.744 μg/mL) lower than that of chloramphenicol (2.019-8.078 μg/mL) against E. coli, P. aeruginosa, and S. marcescens. Prediction of ADME parameters, pharmacokinetics, and substrate promiscuity revealed that these new pyridazines could be promising drug candidates. Cytotoxic studies on rat hepatocytes showed how much safe these new pyridazines on living organisms (IC50 >64 μg/mL). MOE docking studies showed a good overlay of these new pyridazines with co-crystallized ligand within an E. coli DNA gyrase subunit B active sites (4KFG).

Coumarin-containing hybrids and their antibacterial activities.

Infections caused by Gram-positive and -negative bacteria are one of the foremost causes of morbidity and mortality globally. Antibiotics are the mainstay of therapy for bacterial infections, but the emergence and wide spread of drug-resistant pathogens have already become a huge issue for public healthcare systems. The coumarin moiety, which is ubiquitous in nature, could bind to the B subunit of DNA gyrase in bacteria and inhibit DNA supercoiling by blocking the ATPase activity; hence, coumarin derivatives possess potential antibacterial activity. Several coumarin-containing hybrids such as coumermycin A1, clorobiocin, and novobiocin have already been used in clinical practice for the treatment of various bacterial infections; thus, it is conceivable that hybridization of the coumarin moiety with other antibacterial pharmacophores may provide opportunities for the development of novel antibiotics. This review outlines the advances in coumarin-containing hybrids with antibacterial potential in the recent 5 years and the structure-activity relationships are also discussed.

Livestock Brucellosis: Frequency of Mutations Causing Resistance to Fluoroquinolone, Streptomycin and Rifampin

Background: Malta fever caused by the Brucella spp. is an endemic zoonotic infectious disease in Iran. Evaluation of the disease control is essential for socioeconomic and public health-related concerns. Objectives: This study aimed to evaluate the prevalence of Brucella spp. and the frequency of mutations responsible for resistance to rifampin, streptomycin, and fluoroquinolones in sheep from Mianeh, Southwest of West Azarbaijan Province, Iran. Methods: A total number of 1,220 blood samples were collected in Mianeh. Positive samples screened using Rose Bengal Plate Test (RBPT) were subjected to Polymerase Chain Reaction (PCR). Finally, positive samples were investigated for the presence of mutated aminoglycoside adenylyl-transferase-A1 (aadA1) (conventional PCR), DNA gyrase subunit A (gyrA), topoisomerase IV subunit C (parC) (MAMA PCR for both) and RNA polymerase β-subunit (rpoB) (MAS PCR) responsible for antibiotic resistance. Results: There were 41 Brucella abortus Cell Surface Protein 31 Positive (BCSP31+) samples out of 111 RBPT positive samples which 15% (n = 7) of them were obtained from vaccinated sheep. Of the total BCSP31+ samples 9 were carrying mutated aadA1, 3 carrying mutated parC and only one sample carrying mutated rpoB. None of the samples were positive for mutated gyrA. Conclusions: The prevalence of Brucellosis in livestock in the city of Mianeh has been higher than in other areas in Iran, and some antibiotic resistance genes have been identified in livestock specimens. It can be concluded that due to the relatively good efficacy of the vaccines, the need for vaccination in all livestock farms of this city is important.

Design, Synthesis and Antimicrobial Evaluation of Novel 2-Thiobenzimidazole Derivatives: in silico and in vitro Approach

The development of potent antimicrobial agents is more essential due to resistance developed in microorganisms towards the existing drugs. The diversity in the biological retort profile of benzimidazole more attracted the attention to develop novel compounds to its various potential against microorganisms. In present work, designed molecular structures docked against DNA gyrase subunit B and lanosterol 14α-demethylase (LAD) proteins. Interestingly, most of the compounds revealed excellent docking scores and interactions compared with the co-crystal ligands KKK, 1YN of LAD proteins 3LD6, 5V5Z than DNA gyrase subunit B proteins 5L3J and 4P8O. Then, the molecular properties were predicted by the Swiss ADME tool, the compounds showed no violation in Lipinski’s rule and good synthetic accessibility. These compounds synthesized by stirring of 2-mercapto benzimidazole (1), epichlorohydrin (2) in the presence of sodium hydroxide gives 1-(1H-benzo[d]imidazole-2-ylthio)-3- chloropropan-2-ol (3), which upon refluxing with different substituted aliphatic and aromatic amines in methanol produces novel benzimidazole derivatives (4a-l). These compounds were characterized by their melting point, FT-IR, 1H NMR and Mass spectral data. The synthesized molecules screened for antibacterial and antifungal activity. The compound 4l exhibited excellent activity at MIC 0.4 μg/mL against C. albicans. Compounds 4c and 4e showed MIC at 3.12 μg/mL against E. coli and the compounds 4l and 4J exhibited MIC at 3.12 μg/mL against S. aureus. Docking studies and activity result reveals the novel benzimidazole compound 4l has excellent antifungal and antibacterial effect.

The Genome Structure of Ciprofloxacin-Resistant Mycoplasma Hominis Clinical Isolates.

The genome structure of three ciprofloxacin-resistant Mycoplasma hominis clinical isolates was studied using next-generation sequencing on the Illumina platform. The protein sequences of the studied Mycoplasma strains were found to have a high degree of homology. Mycoplasma hominis (M45, M57, MH1866) was shown to have limited biosynthetic capabilities, associated with the predominance of the genes encoding the proteins involved in catabolic processes. Multiple single-nucleotide substitutions causing intraspecific polymorphism of Mycoplasma hominis were found. The genes encoding the efflux systems – ABC transporters (the ATP-binding cassette superfamily) and proteins of the MATE (multidrug and toxic compound extrusion) family – were identified. The molecular mechanism of ciprofloxacin resistance of the Mycoplasma hominis M45 and M57 isolates was found to be associated with the Ser83Leu substitution in DNA gyrase subunit A. In the Mycoplasma hominis MH1866 isolate it was related to the Lys144Arg substitution in topoisomerase IV subunit A.

First Report of Ewingella americana Causing Bacterial Shot Hole on Anoectochilus roxburghii in China

Anoectochilus roxburghii (Wall.) Lindl., known as jinxianlian in Chinese, is a member of the Orchidaceae family. Traditionally, it has been considered as one of the most valuable medicinal plants used for therapeutic treatments. During the period from September to November in 2017 and 2018, symptoms of bacterial shot hole disease were observed in ∼10% of A. roxburghii plants in a 30-ha area (23°88′N; 100°08′E) in Lincang County, Yunnan Province. Chlorosis is the first symptom, and then the leaves turn brown, followed by profuse brown necrotic spotting and scorching. Then, the leaves eventually dry up and become punched out. No symptoms are observed on the stem or root. To identify the possible pathogens, three diseased leaves were disinfected with tap water and then 70% ethanol for 30 s, followed by maceration in sterile distilled water for three times, and 20 µl of the suspension was plated onto nutrient agar (NA) medium and incubated at 28°C for 48 h in the dark. A predominant type of colony was purified on NA, and a representative isolate designated JXL-2 was used for further study. The cultures formed an oyster white lawn and were short rod shaped, with a cell size around 1.5 to 1.3 × 0.6 to 0.8 μm, and were periflagellate with slow motility. The biochemical tests showed that JXL-2 was gram negative, nonfluorescent, and positive for the Voges–Proskauer test, o-nitrophenyl-β-D-galactoside reaction, and esculin hydrolysis. But it does not produce indoles, ureases, H₂S, phenylalanine deaminase, amylase, or lysine decarboxylase, or ornithine decarboxylase. The 16S ribosomal RNA and DNA gyrase subunit B (gyrB) partial genes were amplified using the primers 27F/1492R and UP1/UP2, respectively (Marchesi et al. 1998; Liu et al. 2018) and sequenced (MK460249.1 and MK460250.1). These sequences had 99% nucleotide identity with Ewingella americana in GenBank (KF308476.1, NR 104925.1). Koch’s postulates were fulfilled on 10 healthy leaves of 4-month-old potted A. roxburghii plants in an incubator. Bacterial suspension (0.2 ml, 1.0 × 10⁸ CFU/ml) was extracted with a sterilized syringe and injected into each leaf of A. roxburghii. The same amount of sterilized water was inoculated to 10 more A. roxburghii leaves as a control. The experimental and control groups were incubated in an artificial climate incubator, at 25°C with 12-h light/dark and 85% relative humidity. Symptoms similar to those of diseased leaves in the field were observed in the JXL-2-inoculated group after 15 days, whereas the control group remained healthy. E. americana was consistently reisolated from the inoculated symptomatic leaves, which were identified through 16S rRNA and gyrB nucleotide sequence analysis. Finally, we confirmed the pathogen was E. americana based on morphological, biochemical, and molecular characteristics. It has been reported that the ecological niche or natural source of E. americana is unknown, but it has been isolated from animals, mushrooms, carrots, and even vacuum-packaged meat (Liu et al. 2018; Reyes et al. 2004). To our knowledge, this is the first report of E. americana causing bacterial shot hole disease on A. roxburghii in China and around the world. It would be a new and noteworthy finding that E. americana could cause diseases on plants.

Dual Escherichia coli DNA Gyrase A and B Inhibitors with Antibacterial Activity.

The emergence of multidrug-resistant bacteria is a global health threat necessitating the discovery of new antibacterials and novel strategies for fighting bacterial infections. We report first-in-class DNA gyrase B (GyrB) inhibitor/ciprofloxacin hybrids that display antibacterial activity against Escherichia coli. Whereas DNA gyrase ATPase inhibition experiments, DNA gyrase supercoiling assays, and in vitro antibacterial assays suggest binding of the hybrids to the E. coli GyrA and GyrB subunits, an interaction with the GyrA fluoroquinolone-binding site seems to be solely responsible for their antibacterial activity. Our results provide a foundation for a new concept of facilitating entry of nonpermeating GyrB inhibitors into bacteria by conjugation with ciprofloxacin, a highly permeable GyrA inhibitor. A hybrid molecule containing GyrA and GyrB inhibitor parts entering the bacterial cell would then elicit a strong antibacterial effect by inhibition of both the GyrA and GyrB subunits of DNA gyrase and potentially slow bacterial resistance development.

Genotyping Neisseria gonorrhoeae gyrA and penA antimicrobial genes from remnant Neisseria gonorrhoeae positive Cepheid Xpert® clinical specimens – A feasibility study

Neisseria gonorrhoeae (NG) has developed resistance to most antibiotics, making it increasingly difficult to treat. Previous studies have predicted antimicrobial NG susceptibility based on the antimicrobial gene target DNA gyrase subunit A (gyrA) codon serine 91 and the penicillin-binding protein 2 (penA) using Roche Cobas® and Hologic APTIMA™ clinical specimens. We studied whether similar methods could be used on remnant NG-positive Cepheid Xpert® specimens.

Addressing Neisseria gonorrhoeae Treatment Resistance With the DNA Gyrase A Assay: An Economic Study, United States.

Targeted antibiotics could delay emergence of resistant Neisseria gonorrhoeae. The DNA gyrase subunit A assay predicts susceptibility to ciprofloxacin. A model found that adding a $50 gyrase subunit A test for asymptomatic patients screened for N. gonorrhoeae resulted in cost neutrality. When ciprofloxacin susceptibility was high, a $114 test resulted in savings.

In silico study directed towards identification of the key structural features of GyrB inhibitors targeting MTB DNA gyrase: HQSAR, CoMSIA and molecular dynamics simulations

ABSTRACTMycobacterium tuberculosis DNA gyrase subunit B (GyrB) has been identified as a promising target for rational drug design against fluoroquinolone drug-resistant tuberculosis. In this study, we attempted to identify the key structural feature for highly potent GyrB inhibitors through 2D-QSAR using HQSAR, 3D-QSAR using CoMSIA and molecular dynamics (MD) simulations approaches on a series of thiazole urea core derivatives. The best HQSAR and CoMSIA models based on IC50 and MIC displayed the structural basis required for good activity against both GyrB enzyme and mycobacterial cell. MD simulations and binding free energy analysis using MM-GBSA and waterswap calculations revealed that the urea core of inhibitors has the strongest interaction with Asp79 via hydrogen bond interactions. In addition, cation-pi interaction and hydrophobic interactions of the R2 substituent with Arg82 and Arg141 help to enhance the binding affinity in the GyrB ATPase binding site. Thus, the present study provides crucial structural features and a structural concept for rational design of novel DNA gyrase inhibitors with improved biological activities against both enzyme and mycobacterial cell, and with good pharmacokinetic properties and drug safety profiles.

Allicin, a natural antimicrobial defence substance from garlic, inhibits DNA gyrase activity in bacteria

Allicin (diallylthiosulfinate) is a potent antimicrobial substance, produced by garlic tissues upon wounding as a defence against pathogens and pests. Allicin is a reactive sulfur species (RSS) that oxidizes accessible cysteines in glutathione and proteins. We used a differential isotopic labelling method (OxICAT) to identify allicin targets in the bacterial proteome. We compared the proteomes of allicin-susceptible Pseudomonas fluorescens Pf0-1 and allicin-tolerant PfAR-1 after a sublethal allicin exposure. Before exposure to allicin, proteins were in a predominantly reduced state, with approximately 77% of proteins showing less than 20% cysteine oxidation. Protein oxidation increased after exposure to allicin, and only 50% of proteins from allicin-susceptible Pf0-1, but 65% from allicin-tolerant PfAR-1, remained less than 20% oxidised. DNA gyrase was identified as an allicin target. Cys433 in DNA gyrase subunit A (GyrA) was approximately 6% oxidized in untreated bacteria. After allicin treatment the degree of Cys433 oxidation increased to 55% in susceptible Pf0-1 but only to 10% in tolerant PfAR-1. Allicin inhibited E. coli DNA gyrase activity in vitro in the same concentration range as nalidixic acid. Purified PfAR-1 DNA gyrase was inhibited to greater extent by allicin in vitro than the Pf0-1 enzyme. Substituting PfAR-1 GyrA into Pf0-1 rendered the exchange mutants more susceptible to allicin than the Pf0-1 wild type. Taken together, these results suggest that GyrA was protected from oxidation in vivo in the allicin-tolerant PfAR-1 background, rather than the PfAR-1 GyrA subunit being intrinsically less susceptible to oxidation by allicin than the Pf0-1 GyrA subunit. DNA gyrase is a target for medicinally important antibiotics; thus, allicin and its analogues may have potential to be developed as gyrase inhibitors, either alone or in conjunction with other therapeutics.