Novel Class Of Antimicrobial Agents Research Articles

Potent Inhibition of E. coli DXP Synthase by a gem-Diaryl Bisubstrate Analog.

New antimicrobial strategies are needed to address pathogen resistance to currently used antibiotics. Bacterial central metabolism is a promising target space for the development of agents that selectively target bacterial pathogens. 1-Deoxy-d-xylulose 5-phosphate synthase (DXPS) converts pyruvate and d-glyceraldehyde 3-phosphate (d-GAP) to DXP, which is required for synthesis of essential vitamins and isoprenoids in bacterial pathogens. Thus, DXPS is a promising antimicrobial target. Toward this goal, our lab has demonstrated selective inhibition of Escherichia coli DXPS by alkyl acetylphosphonate (alkylAP)-based bisubstrate analogs that exploit the requirement for ternary complex formation in the DXPS mechanism. Here, we present the first DXPS structure with a bisubstrate analog bound in the active site. Insights gained from this cocrystal structure guided structure-activity relationship studies of the bisubstrate scaffold. A low nanomolar inhibitor (compound 8) bearing a gem-dibenzyl glycine moiety conjugated to the acetylphosphonate pyruvate mimic via a triazole-based linker emerged from this study. Compound 8 was found to exhibit slow, tight-binding inhibition, with contacts to E. coli DXPS residues R99 and R478 demonstrated to be important for this behavior. This work has discovered the most potent DXPS inhibitor to date and highlights a new role of R99 that can be exploited in future inhibitor designs toward the development of a novel class of antimicrobial agents.

Novel Benzimidazole linked piperidine derivatives screened for antibacterial and antioxidant properties with Density Functional and Molecular Mechanic tools

In the present work, the scope for obtaining an active and less toxic anti-microbial and antioxidant agent, was explored to synthesize novel benimidazole semicarbazide derivatives (F1-F5) by conventional method. A novel series of 1-(substituted benzylidene)-4-(4-(3-oxo-3-(1-(piperidin-1-ylmethyl)-1Hbenzoimidazol-2-yl) prop-1-enyl) phenyl) semicarbazide F1-F5 were synthesized from o-phenylenediamine by using multi-step synthesis. IR, 1H NMR, 13C NMR Mass spectroscopy and elemental analysis data of the synthesized compounds are found to be in accordance with the assigned structures. Under DFT, B3LYP/6311G method was used to investigate novel compounds, their electronic characteristics were evaluated using the same. All the title compounds were evaluated for their in-vitro anti-microbial activity against three bacteria and three fungi by the agar well diffusion method at three different concentrations and for antioxidant activity by the DPPH (2,2-diphenyl-1-picrylhydrazyl) Scavenging method. Among the synthesized compounds, F2 and F4 showed significant antibacterial activity, whereas compound F3 showed significant antifungal activity. Compound F1 showed moderate to good antibacterial and antifungal activity against selected strains with the SAR study. It was observed that the compounds having electron withdrawing moiety exhibited better antibacterial activity than compounds having electron donating ones, whereas in antifungal it was viceversa. Out of five compounds, F2 exhibited the most potent antibacterial and antifungal activity, while F3 exhibited potent antioxidant activity. As a result, the compounds F2 and F3 could serve as pilot molecules for the further development of a novel class of antimicrobial agents.

A Novel Biocidal Nanocomposite: Spherical Silica with Silver Ions Anchored at the Surface.

This article is devoted to a novel class of antimicrobial agents: nanocomposites composed of spherical silica and silver ions located at the silica's surface with the assumed distribution. Such materials are in high demand due to the increasing threat from bacterial strains that are becoming resistant to currently known antibiotics. In particular, we focus on materials that make it possible to limit the growth of bacterial colonies on a variety of tactile surfaces. In this paper, we present a method for preparing a silica-based nanocomposite containing silver ions and the analysis of their antimicrobial properties. Our research revealed that the presence of tested nanocomposite induces very high oxidative stress in the bacteria cell, damaging and modifying bacterial DNA, creating oxidized guanines, cytosines, or adenines, which causes its very rapid destruction, leading to cell death.

Targeting Multiresistant Gram-Positive Bacteria by Ruthenium, Osmium, Iridium and Rhodium Half-Sandwich Type Complexes With Bidentate Monosaccharide Ligands.

Bacterial resistance to antibiotics is an ever-growing problem in heathcare. We have previously identified a set of osmium(II), ruthenium(II), iridium(III) and rhodium(III) half-sandwich type complexes with bidentate monosaccharide ligands possessing cytostatic properties against carcinoma, lymphoma and sarcoma cells with low micromolar or submicromolar IC50 values. Importantly, these complexes were not active on primary, non-transformed cells. These complexes have now been assessed as to their antimicrobial properties and found to be potent inhibitors of the growth of reference strains of Staphylococcus aureus and Enterococcus faecalis (Gram-positive species), though the compounds proved inactive on reference strains of Pseudomonas aerugonisa, Escherichia coli, Candida albicans, Candida auris and Acinetobacter baumannii (Gram-negative species and fungi). Furthermore, clinical isolates of Staphylococcus aureus and Enterococcus sp. (both multiresistant and susceptible strains) were also susceptible to the organometallic complexes in this study with similar MIC values as the reference strains. Taken together, we identified a set of osmium(II), ruthenium(II), iridium(III) and rhodium(III) half-sandwich type antineoplastic organometallic complexes which also have antimicrobial activity among Gram-positive bacteria. These compounds represent a novel class of antimicrobial agents that are not detoxified by multiresistant bacteria suggesting a potential to be used to combat multiresistant infections.

Solid-phase synthesis of novel antimicrobial peptoids with α- and β-chiral side chains.

Bacterial resistance to conventional antibiotics poses an immense threat to human health and consequently many bacterial infections arise from multi-drug resistant pathogens. It is, therefore, necessary to continue to develop novel antimicrobials. Peptoids are a novel class of antimicrobial agents that mimic the structures of peptides. These N-substituted glycines differ from peptides in the side chain attachment site where in peptoids, the side chain functionality is introduced at the nitrogen rather than the α-carbon in peptides. During the process of design and development of antimicrobial peptoids, several key elements such as charge and amphiphilicity appear to guide peptoid bioactivity against bacterial pathogens. In this study, we report a quick synthesis of three novel cationic antimicrobial peptoids that contain charged, hydrophobic, and chiral monomers. This study is the first to use a monomer that contains both charge and chiral center for the design of the novel peptoid sequences.

Oxazolidinone-containing Hybrids with Antibacterial Activity against Methicillin-resistant Staphylococcus aureus (MRSA): A Mini-review.

The increasing danger of methicillin-resistant Staphylococcus aureus (MRSA) and the limited therapeutic options for invasive MRSA infections make an urgent demand for the development of novel anti-MRSA agents. Oxazolidinone derivatives could inhibit protein synthesis by acting on the ribosomal 50S subunit of the bacteria and prevent the formation of a functional 70S initiation complex, so oxazolidinones are a novel class of antimicrobial agents with potential activity against a wide range of clinically significant multidrug-resistant Gram-positive pathogens. However, oxazolidinones such as linezolid are associated with significant adverse events, and myelosuppression represents the main unfavorable side effects. Moreover, MRSA isolates that are resistant to oxazolidinones have already emerged. Hybridization of oxazolidinone with other antibacterial pharmacophores has the potential to interact with multiple targets or to counterbalance the known side effects associated with each pharmacophore. Thus, oxazolidinone-containing hybrids are useful scaffolds for the development of novel anti-MRSA agents. This review covers the recent advances of oxazolidinonecontaining hybrids with anti-MRSA activity developed in the last decade to set up the direction for the design and development of oxazolidinone-containing hybrids with high efficiency and low toxicity.

Discovery of a Novel Antimicrobial Agent by the Virtual Screening of a Library of Small Molecules.

A virtual screening approach based upon a combination of docking and pharmacophore methods was utilized on a library of 1.4 million molecules to identify novel antimicrobial agents, which may potentially act via inhibition of the caseinolytic protease. Using this method, compound 6 was found to be bactericidal against three staphylococcal species (minimum inhibitory concentration (MIC)=4-16 μg/mL). Further, subsequent structural optimization of 6 led to the identification of compound 24, which was shown to be the most potent analog within the series (MIC=4 μg/mL) and outperforming the antibiotic controls for two of the staphylococcal species. The newly discovered antimicrobial agent (24) demonstrated excellent in silico ADME properties and was non-toxic when tested on two human skin cell lines. As such, compound 24 has the potential for use as a lead molecule in the development of a novel class of antimicrobial agents.

Antibacterial activity of a scorpion-derived peptide and its derivatives in vitro and in vivo

Antimicrobial peptides have recently become extremely popular as a novel class of antimicrobial agents. AMP MK049518 (FLGLLGSVLGSVLPSIFK), identified from the crab-scorpion Didymocentrus krausi, only possesses significant antibacterial activity against Gram-positive bacteria. In this study, a derivative G2K–S3K was designed with an excellent antibacterial spectrum and significantly higher antibacterial activity compared to the natural peptide. G2K–S3K also demonstrated excellent serum- and thermal-stability and did not induce bacterial resistance. In the Staphylococcus aureus and Pseudomonas aeruginosa -induced skin infection in mice, G2K–S3K significantly decreased bacterial counts in the wound by topical application. Thus, G2K–S3K could be a potent topical anti-infective agent against the skin infection caused by S. aureus and P. aeruginosa.

The Role of Orientation of Surface Bound Dihydropyrrol-2-ones (DHP) on Biological Activity.

Quorum sensing (QS) signaling system is important for bacterial growth, adhesion, and biofilm formation resulting in numerous infectious diseases. Dihydropyrrol-2-ones (DHPs) represent a novel class of antimicrobial agents that inhibit QS, and are less prone to develop bacterial resistance due to their non-growth inhibition mechanism of action which does not cause survival pressure on bacteria. DHPs can prevent bacterial colonization and quorum sensing when covalently bound to substrates. In this study, the role of orientation of DHP compounds was investigated after covalent attachment by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) coupling reaction to amine-functionalized glass surfaces via various positions of the DHP scaffold. The functionalized glass surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements and tested for their in vitro biological activity against S. aureus and P. aeruginosa. DHPs attached via the N-1 position resulted in the highest antibacterial activities against S. aureus, while no difference was observed for DHPs attached either via the N-1 position or the C-4 phenyl ring against P. aeruginosa.

DESIGN AND SYNTHESIS OF NOVEL 1-((DIMETHYLAMINO)METHYL)-3-(4-(3-(SUBSTITUTE DPHENYL)-4-OXOTHIAZOLIDIN-2-YL)PHENYLIMINO)-5-NITROINDOLIN-2-ONES AS POTENT ANTITUBERCULAR AGENTS

Objective: Isatins have emerged as antimicrobial agents due to their broad spectrum of in vitro and in vivo antimicrobial activities. In addition, thiazolidinone also reported to possess various biological activities particularly antimicrobial activity. Due to the importance, we planned to synthesize compounds with isatin functionality coupled with thiazolidinone as possible antitubercular and antimicrobial agents which could furnish better therapeutic results.
 Methods: In vitro Mycobacterium tuberculosis method and agar streak dilution test are used to estimate antitubercular and antimicrobial potency of title analogs, respectively. Minimum inhibitory concentration of entire title compounds was determined against all tested microorganism such as M. tuberculosis, four Gram-positive, three Gram-negative bacteria, and two fungi.
 Results: A series of new thiazolidinone substituted Schiff and Mannich bases of 5-nitroisatins were designed and synthesized by a multistep synthesis from isatin. Structures of synthesized compounds are characterized using Fourier-transform infrared, proton nuclear magnetic resonance, mass spectroscopy, and bases of elemental analysis. Mild to good antitubercular and antimicrobial activity was showed by synthesized 5-nitroisatin analogs. The relationship between the biological activity and the functional group variation of the tested compounds was discussed.
 Conclusion: 3-(4-(3-(4-Aminophenyl)-4-oxothiazolidin-2-yl)phenylimino)-1-((dimethyl amino)methyl)-5-nitroindolin-2-one 6 and 3-(4-(3- (2-aminophenyl)-4-oxothiazolidin-2-yl)phenylimino)-1-((dimethylamino)methyl)-5-nitroindolin-2-one 13 were found to be the most potent compounds of this series which might be extended as a novel class of antimicrobial agents.

Novel indole-thiazolidinone conjugates: Design, synthesis and whole-cell phenotypic evaluation as a novel class of antimicrobial agents

In connection with our research program on the development of novel anti-tubercular candidates, herein we report the design and synthesis of two different sets of indole-thiazolidinone conjugates (8a,b; 11a-d) and (14a-k; 15a-h). The target compounds were evaluated for their in vitro antibacterial and antifungal activities against selected human pathogens viz. Staphylococcus aureus (Gram positiveve), Pseudomonas aeruginosa, Escherichia coli (Gram negative), Mycobacterium tuberculosis (Acid-fast bacteria), Aspergillus fumigates and Candida albicans (fungi). Moreover, eukaryotic cell-toxicity was tested via an integrated ex vivo drug screening model in order to evaluate the selective therapeutic index (SI) towards antimicrobial activity when microbes are growing inside primary immune cells. Also, the cytotoxicity towards a panel of cancer cell lines and human lung fibroblast normal cell line, WI-38 cells, was explored to assure their safety. Compound 15b emerged as a hit in this study with potent broad spectrum antibacterial (MIC: 0.39–0.98 μg/mL) and antifungal (MIC: 0.49–0.98 μg/mL) activities, in addition to its ability to kill mycobacteria M. aurum inside an infected macrophage model with good therapeutic window. Moreover, compound 15b displayed promising activity towards resistant bacteria strains MRSA and VRE with MIC values equal 3.90 and 7.81 μg/mL, respectively. These results suggest compound 15b as a new therapeutic lead with good selectivity for further optimization and development.

Synergistic activity of an OmpA inhibitor and colistin against colistin-resistant Acinetobacter baumannii: mechanistic analysis and in vivo efficacy.

Preventing bacterial contact with host cells can provide an additional approach to tackling MDR Acinetobacter baumannii. Recently, we identified AOA-2 as a potential blocker of A. baumannii outer membrane protein A without presenting bactericidal activity. Here, we aimed to study whether AOA-2 can increase the activity of colistin against colistin-resistant A. baumannii in vitro and in vivo. Reference and clinical A. baumannii strains susceptible and resistant to colistin (CST-S and CST-R) were used. Microdilution and time-kill curve assays were performed to determine the synergy between AOA-2 and colistin. SDS-PAGE assays with CST-S and CST-R outer membrane proteins and MALDI-TOF-TOF (MS-MS/MS) analysis were performed to determine the AOA-2 and colistin synergy mechanism. In a murine peritoneal sepsis model, the therapeutic efficacy of AOA-2 (10 mg/kg/24 h) in combination with a sub-optimal dose of colistin (10 mg/kg/24 h) against CST-R was evaluated by determining the bacterial load in tissues and blood, and mouse survival. We showed that AOA-2 increased the in vitro colistin susceptibility of reference and clinical CST-S and CST-R strains. This combination also enhanced their killing activity after 24 h of drug exposure. This synergy is mediated by the overexpression of Omp25. In vivo, the combination of AOA-2 with colistin significantly reduced the bacterial load in tissues and blood, and increased mouse survival, compared with colistin monotherapy. We identified a novel class of antimicrobial agents that has proven to be effective in combination with colistin in an experimental model of severe infection by CST-R A. baumannii.

Synthesis and evaluation of antibacterial and antifungal activities of 4-thiazolidinones and 2-azetidinones derivatives from chalcone

(E)-3-(thiophen-2-yl)-1-(4-methylphenyl)-prop-2-en-1-one 1 was obtained from the reaction of thiophene-2-aldehyde with p-methyl acetophenone. The treatment of 1 with guanidine nitrate produced 4-thiophen-2-yl-6-(4-methylphenyl)-pyrimidin-2-ylamine 2. The synthesis of N-substituted benzylidine-4-(4-methylphenyl)-6-(thiophen-2-yl) pyrimidin-2-amines 3a–j was performed by the treatment of compound 2 with the corresponding aromatic aldehydes. The reaction of 3a–j with thioglycolic acid and thiolactic acid formed the corresponding 3-[4-(4-methyl-phenyl)-6-thiophen-2-yl-pyrimidin-2-yl]-2-(substituted-phenyl)-thiazolidin-4-ones 4a–j and 3-[4-(4-methyl-phenyl)-6-thiophen-2-yl-pyrimidin-2-yl]-2-(substituted-phenyl)-5-methyl-thiazolidin-4-ones 5a–j and with chloroacetylchloride, it gives 3-chloro-1-[4-(4-methyl-phenyl)-6-thiophen-2-yl-pyrimidin-2-yl]-4-(substituted-phenyl)-azetidin-2-ones 6a–j. Newer analogues were characterized by infrared spectrum, 1H nuclear magnetic resonance, 13C nuclear magnetic resonance spectroscopy and elemental analyses. The newly synthesized analogues were then examined for their antimicrobial activity against some bacterial and fungal strains as two Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa), two Gram-positive bacteria (Staphylococcus aureus, Streptococcus pyogenes) and two fungal species (Candida albicans, Aspergillus niger, Aspergillus Clavatus) to develop a novel class of antimicrobial agents.

The tuberculocidal activity of polyaniline and functionalised polyanilines.

Tuberculosis is considered a leading cause of death worldwide. More than 95% of cases and deaths occur in low- and middle-income countries. In resource-limited countries, hospitals often lack adequate facilities to manage and isolate patients with infectious tuberculosis (TB), relying instead on personal protective equipment, such as facemasks, to reduce nosocomial transmission of the disease. Facemasks impregnated with an antimicrobial agent may be a cost-effective way of adding an extra level of protection against the spread of TB by reducing the risk of disease transmission. Conducting polymers, such as polyaniline (PANI), and their functionalised derivatives are a novel class of antimicrobial agents with potential as non-leaching additives to provide contamination resistant surfaces. We have investigated the antimicrobial action of PANI and a functionalised derivative, poly-3-aminobenzoic acid (P3ABA), against mycobacteria and have determined the optimal treatment time and concentration to achieve significant knockdown of Mycobacterium smegmatis and Mycobacterium tuberculosis on an agar surface. Results indicated that P3ABA is a potential candidate for use as an anti-tuberculoid agent in facemasks to reduce TB transmission.

A Novel Class of Antimicrobial Agents: Ceragenins (Cationic Steroid Antibiotics)

A Novel Class of Antimicrobial Agents: Ceragenins (Cationic Steroid Antibiotics)

Antibacterial activity of new peptides from barbel protein hydrolysates and mode of action via a membrane damage mechanism against Listeria monocytogenes

There is great interest in the development of antimicrobial peptides as a potentially novel class of antimicrobial agents. In this study we evaluated the mode of action of new peptides (Gly-Val-His, Trp-His-Arg, Trp-His-Phe, Pro-Pro-Ser-Ser, Ala-Ala-Ala-Leu, Ala-Ala-Gly-Gly-Val, Ala-Ala-Val-Lys-Met, Ala-Ser-Ser-Ser), previously characterized, from barbel protein hydrolysates against Listeria monocytogenes via a membrane damage mechanism. The minimum inhibitory concentrations (MIC) of these peptides toward six strains and their hemolytic activity toward bovine erythrocytes were determined.Prediction of peptide secondary structure indicated that these peptides should have random coil structures and high content of hydrophobic amino acids. In addition, results of the determination of extracellular potassium, which is considered a good marker of membrane permeability, revealed that treatment with pure barbel peptides could cause morphological changes of L. monocytogenes and destruction of the cell integrity via irreversible membrane damage. The results could provide information for investigating the antibacterial model of antibacterial peptides derived from fish protein hydrolysates.

Enhanced Antimicrobial Activity of AamAP1-Lysine, a Novel Synthetic Peptide Analog Derived from the Scorpion Venom Peptide AamAP1.

There is great interest in the development of antimicrobial peptides as a potentially novel class of antimicrobial agents. Several structural determinants are responsible for the antimicrobial and cytolytic activity of antimicrobial peptides. In our study, a new synthetic peptide analog, AamAP1-Lysine from the naturally occurring scorpion venom antimicrobial peptide AamAP1, was designed by modifying the parent peptide in order to increase the positive charge and optimize other physico-chemical parameters involved in antimicrobial activity. AamAP1-Lysine displayed potent antibacterial activity against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration was in the range of 5 to 15 µM with a 10 fold increase in potency over the parent peptide. The hemolytic and antiproliferative activity of AamAP1-Lysine against eukaryotic mammalian cells was minimal at the concentration range needed to inhibit bacterial growth. The antibacterial mechanism analysis indicated that AamAP1-Lysine is probably inducing bacterial cell death through membrane damage and permeabilization determined by the release of β-galactosidase enzyme from peptide treated E. coli cells. DNA binding studies revealed that AamAP1-Lysine caused complete retardation of DNA migration and could display intracellular activities in addition to the membrane permeabilization mode of action reported earlier. In conclusion, AamAP1-Lysine could prove to be a potential candidate for antimicrobial drug development in future studies.

1,4-Diaryl-2-mercaptoimidazoles derivatives as a novel class of antimicrobial agents: design, synthesis, and computational studies

In search of a new class of potential antimicrobial agents, some 1,4-diaryl-2-mercaptoimidazoles (5a–5h) were prepared by employing a mild and green approach in which substituted anilines 3 were treated with phenacylbromide 2 in the presence of Na2CO3/K2CO3 followed by the treatment of a solid catalyst, p-TSA (para toluene sulphonic acid), to give imidazole derivatives in excellent yields. All compounds were characterized on the basis of their UV, IR, 1H & 13C NMR, and Mass spectral data. Pharmacotherapeutic potential with the possible molecular mechanism of action of the compounds were estimated on the basis of prediction of activity spectra for substances (PASS) prediction results obtained by PharmaExpert software. The activity profile predicted by PASS was further supported by some theoretical calculations, in vitro experimental evaluation, and then validated via docking studies. In vitro antimicrobial potential was evaluated via agar well diffusion assay against five bacterial strains (one Gram-positive and four Gram-negative bacteria) and two pathogenic fungi. The antibacterial activity of the test compounds 5a–h against P. aeruginosa was found to be similar to that of Ceftriaxone, an efficient second generation antibiotic. Compound 5h displayed promising broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacterial strains. Except 4e, almost all the compounds were found to have an excellent level of antifungal activity against C. albicans when compared with a standard drug, Fluconazole. The docking results obtained confirm the interactions of compounds (5a–h) with the active site of cytochrome P450 14 α-sterol demethylase. Thus, it is concluded that the compounds considered under this investigation have an excellent potential to be acted, as antimicrobial leads in the future medicinal chemistry.

Characterization of Antimicrobial Peptides toward the Development of Novel Antibiotics

Antimicrobial agents have eradicated many infectious diseases and significantly improved our living environment. However, abuse of antimicrobial agents has accelerated the emergence of multidrug-resistant microorganisms, and there is an urgent need for novel antibiotics. Antimicrobial peptides (AMPs) have attracted attention as a novel class of antimicrobial agents because AMPs efficiently kill a wide range of species, including bacteria, fungi, and viruses, via a novel mechanism of action. In addition, they are effective against pathogens that are resistant to almost all conventional antibiotics. AMPs have promising properties; they directly disrupt the functions of cellular membranes and nucleic acids, and the rate of appearance of AMP-resistant strains is very low. However, as pharmaceuticals, AMPs exhibit unfavorable properties, such as instability, hemolytic activity, high cost of production, salt sensitivity, and a broad spectrum of activity. Therefore, it is vital to improve these properties to develop novel AMP treatments. Here, we have reviewed the basic biochemical properties of AMPs and the recent strategies used to modulate these properties of AMPs to enhance their safety.

Inhibition of Yersinia pestis DNA adenine methyltransferase in vitro by a stibonic acid compound: identification of a potential novel class of antimicrobial agents.

Multiple antibiotic resistant strains of plague are emerging, driving a need for the development of novel antibiotics effective against Yersinia pestis. DNA adenine methylation regulates numerous fundamental processes in bacteria and alteration of DNA adenine methlytransferase (Dam) expression is attenuating for several pathogens, including Y. pestis. The lack of a functionally similar enzyme in humans makes Dam a suitable target for development of novel therapeutics for plague. Compounds were evaluated for their ability to inhibit Dam activity in a high-throughput screening assay. DNA was isolated from Yersinia grown in the presence of lead compounds and restricted to determine the effect of inhibitors on DNA methylation. Transcriptional analysis was undertaken to determine the effect of an active inhibitor on virulence-associated phenotypes. We have identified a series of aryl stibonic acids which inhibit Dam in vitro. The most active, 4-stibonobenzenesulfonic acid, exhibited a competitive mode of inhibition with respect to DNA and a K(i) of 6.46 nM. One compound was found to inhibit DNA methylation in cultured Y. pestis. The effects of this inhibition on the physiology of the cell were widespread, and included altered expression of known virulence traits, including iron acquisition and Type III secretion. We have identified a novel class of potent Dam inhibitors. Treatment of bacterial cell cultures with these inhibitors resulted in a decrease in DNA methylation. Expression of virulence factors was affected, suggesting these inhibitors may attenuate bacterial infectivity and function as antibiotics.