Development of novel antibacterial agents against methicillin-resistant Staphylococcus aureus

Sulfur (SⅥ)-containing heterocyclic hybrids as antibacterial agents against methicillin-resistant Staphylococcus aureus (MRSA) and its SAR

The discovery of new small molecule-based inhibitors is an attractive field in medicinal chemistry. Structurally diversified heterocyclic derivatives have been investigated to combat multi-drug resistant bacterial infections and they offers several mechanism of action. Methicillin-resistant Staphylococcus aureus (MRSA) is becoming more and more deadly to humans because of its simple method of transmission, quick development of antibiotic resistance, and ability to cause hard-to-treat skin and filmy diseases. The sulfur (SVI) particularly sulfonyl and sulfonamide based heterocyclic moieties, have found to be good anti-MRSA agents. The development of new nontoxic, economical and highly active sulfur (SVI) containing derivatives has become hot research topics in drug discovery research. Presently, more than 150 FDA approved Sulfur (SVI)-based drugs are available in the market, and they are widely used to treat various types of diseases with different therapeutic potential. The present collective data provides the latest advancements in Sulfur (SVI)-hybrid compounds as antibacterial agents against MRSA. It also examines the outcomes of in-vitro and in-vivo investigations, exploring potential mechanisms of action and offering alternative perspectives on the structure-activity relationship (SAR). Sulfur (SVI)-hybrids exhibits synergistic effects with existing drugs to provide antibacterial action against MRSA.

Fluorinated azoles as effective weapons in fight against methicillin-resistance staphylococcus aureus (MRSA) and its SAR studies

The rapid spread of Methicillin-resistant Staphylococcus aureus (MRSA) and its difficult-to-treat skin and filmsy diseases are making MRSA a threat to human life. The most dangerous feature is the fast emergence of MRSA resistance to all recognized antibiotics, including vancomycin. The creation of novel, effective, and non-toxic drug candidates to combat MRSA isolates is urgently required. Fluorine containing small molecules have taken a centre stage in the field of drug development. Over the last 50 years, there have been a growing number of fluorinated compounds that have been approved since the clinical usage of fluorinated corticosteroids in the 1950 s and fluoroquinolones in the 1980 s. Due to its advantages in terms of potency and ADME (absorption, distribution, metabolism, and excretion), fluoro-pharmaceuticals have been regarded as a potent and useful tool in the rational drug design method. The flexible bioactive fluorinated azoles are ideal candidates for the development of new antibiotics. This review summarizes the decade developments of fluorinated azole derivatives with a wide antibacterial activity against diverged MRSA strains. In specific, we correlated the efficacy of structurally varied fluorinated azole analogues including thiazole, benzimidazole, oxadiazole and pyrazole against MRSA and discussed different angles of structure-activity relationship (SAR).

Evaluation of the antimicrobial efficacy of different nonsteroidal anti-inflammatory drugs alone or in combination with calcium hydroxide intracanal medicament: an in vitro study

This study explored the antimicrobial effects of ketoprofen, piroxicam, and celecoxib alone or combined with calcium hydroxide (CH) against two strains of Enterococcus faecalis (E. faecalis) and assessed the influence of such combinations on the pH of CH. Minimum inhibitory concentrations (MICs) of the three tested NSAIDs were determined. Tested pastes were placed into wells punched in seeded agar plates and the bacterial inhibition zones were measured. Antibiofilm activity was assessed against 3 weeks of biofilm induced in bovine dentine blocks. The pH of the pastes was measured at four-time intervals. MIC values were 3.12, 25, and 25 mg/ml for ketoprofen, piroxicam, and celecoxib, respectively, and were similar for both bacterial strains except for celecoxib, which showed 8% growth at the highest tested concentration against vancomycin-resistant E. faecalis. Ketoprofen had the largest mean inhibition zone that was comparable to CH. None of the six tested pastes exhibited antibiofilm activity of a significant level in comparison to CH. A noticeable increase in the antibiofilm activity was found when 20% NSAIDs were added to CH while maintaining an alkaline pH. Ketoprofen was found to be the most effective among the tested NSAIDs. Although its effect was comparable to CH, adding ketoprofen at a ratio of 20% resulted in 50% higher antimicrobial action than CH alone. Accordingly, incorporating NSAIDs in inter-appointment dressing has the potential to utilize their anti-inflammatory, local analgesic, and antibacterial actions, which overcome the limitations of CH and improve the outcome of root canal treatment.

2,4-Diacetylphloroglucinol (DAPG) derivatives rapidly eradicate methicillin-resistant staphylococcus aureus without resistance development by disrupting membrane

Methicillin-resistant Staphylococcus aureus (MRSA) causes severe public health challenges throughout the world, and the multi-drug resistance (MDR) of MRSA to antibiotics necessitates the development of more effective antibiotics. Natural 2,4-diacetylphloroglucinol (DAPG), produced by Pseudomonas, displays moderate inhibitory activity against MRSA. A series of DAPG derivatives was synthesized and evaluated for their antibacterial activities, and some showed excellent activities (MRSA MIC = 0.5-2 μg/mL). Among these derivatives, 7g demonstrated strong antibacterial activity without resistance development over two months. Mechanistic studies suggest that 7g asserted its activity by targeting bacterial cell membranes. In addition, 7g exhibited significant synergistic antibacterial effects with oxacillin both in vitro and in vivo, with a tendency to eradicate MRSA biofilms. 7g is a promising lead for the treatment of MRSA.

Challenges and Opportunities for Celecoxib Repurposing

Drug repositioning, also known as drug repurposing, reprofiling, or rediscovery, is considered to be one of the most promising strategies to accelerate the development of new original drug products. Multiple examples of successful rediscovery or therapeutic switching of old molecules that did not show clinical benefits or safety in initial trials encourage the following of the discovery of new therapeutic pathways for them. This review summarizes the efforts that have been made, mostly over the last decade, to identify new therapeutic targets for celecoxib. To achieve this goal, records gathered in MEDLINE PubMed and Scopus databases along with the registry of clinical trials by the US National Library of Medicine at the U.S. National Institutes of Health were explored. Since celecoxib is a non-steroidal anti-inflammatory drug that represents the class of selective COX-2 inhibitors (coxibs), its clinical potential in metronomic cancer therapy, the treatment of mental disorders, or infectious diseases has been discussed. In the end, the perspective of a formulator, facing various challenges related to unfavorable physicochemical properties of celecoxib upon the development of new oral dosage forms, long-acting injectables, and topical formulations, including the latest trends in the pharmaceutical technology, such as the application of mesoporous carriers, biodegradable microparticles, lipid-based nanosystems, or spanlastics, was presented.

YidC as a potential antibiotic target

The membrane insertase YidC, is an essential bacterial component and functions in the folding and insertion of many membrane proteins during their biogenesis. It is a multispanning protein in the inner (cytoplasmic) membrane of Escherichia coli that binds its substrates in the "greasy slide" through hydrophobic interaction. The hydrophilic part of the substrate transiently localizes in the groove of YidC before it is translocated into the periplasm. The groove, which is flanked by the greasy slide, is within the center of the membrane, and provides a promising target for inhibitors that would block the insertase function of YidC. In addition, since the greasy slide is available for the binding of various substrates, it could also provide a binding site for inhibitory molecules. In this review we discuss in detail the structure and the mechanism of how YidC interacts not only with its substrates, but also with its partner proteins, the SecYEG translocase and the SRP signal recognition particle. Insight into the substrate binding to the YidC catalytic groove is presented. We wind up the review with the idea that the hydrophilic groove would be a potential site for drug binding and the feasibility of YidC-targeted drug development.

AR-12 Has a Bactericidal Activity and a Synergistic Effect with Gentamicin against Group A Streptococcus

Streptococcus pyogenes (group A Streptococcus (GAS) is an important human pathogen that can cause severe invasive infection, such as necrotizing fasciitis and streptococcal toxic shock syndrome. The mortality rate of streptococcal toxic shock syndrome ranges from 20% to 50% in spite of antibiotics administration. AR-12, a pyrazole derivative, has been reported to inhibit the infection of viruses, intracellular bacteria, and fungi. In this report, we evaluated the bactericidal activities and mechanisms of AR-12 on GAS infection. Our in vitro results showed that AR-12 dose-dependently reduced the GAS growth, and 2.5 μg/mL of AR-12 significantly killed GAS within 2 h. AR-12 caused a remarkable reduction in nucleic acid and protein content of GAS. The expression of heat shock protein DnaK and streptococcal exotoxins was also inhibited by AR-12. Surveys of the GAS architecture by scanning electron microscopy revealed that AR-12-treated GAS displayed incomplete septa and micro-spherical structures protruding out of cell walls. Moreover, the combination of AR-12 and gentamicin had a synergistic antibacterial activity against GAS replication for both in vitro and in vivo infection. Taken together, these novel findings obtained in this study may provide a new therapeutic strategy for invasive GAS infection.

The Galactose-Binding Lectin Isolated from Vatairea macrocarpa Seeds Enhances the Effect of Antibiotics Against Staphylococcus aureus-Resistant Strain

The use of natural products together with standard antimicrobial drugs has recently received more attention as a strategy to combat infectious diseases caused by multidrug-resistant (MDR) microorganisms. This study aimed to evaluate the capacity of a galactose-binding lectin from Vatairea macrocarpa seeds (VML) to modulate antibiotic activity against standard and MDR Staphylococcus aureus and Escherichia coli bacterial strains. The minimum inhibitory concentration (MIC) obtained for VML against all strains was not clinically relevant (MIC ≥ 1024 μg/mL). However, when VML was combined with the antibacterial drugs gentamicin, norfloxacin and penicillin, a significant increase in antibiotic activity was observed against S. aureus, whereas the combination of VML and norfloxacin presented decreased and, hence, antagonistic antibiotic activity against E. coli. By its inhibition of hemagglutinating activity, gentamicin (MIC = 50 mM) revealed its interaction with the carbohydrate-binding site (CBS) of VML. Using molecular docking, it was found that gentamicin interacts with residues that constitute the CBS of VML with a score of - 120.79 MDS. It is this interaction between the antibiotic and the lectin's CBS that may be responsible for the enhanced activity of gentamicin in S. aureus. Thus, our results suggest that the VML can be an effective modulating agent against S. aureus. This is the first study to report the effect of lectins as modulators of bacterial sensitivity, and as such, the outcome of this study could lay the groundwork for future research involving the use of lectins and conventional antibiotics against such infectious diseases such as community-acquired methicillin-resistant S. aureus (MRSA).

Repurposing celecoxib analogues as leads for antibiotics

There is an urgent need for new antibiotics and alternative strategies to combat bacterial pathogens. Molecular docking, antibacterial evaluation in vitro and in vivo, cytotoxicity assessment and enzyme inhibition analyses were performed. Compound 12 exhibited antimicrobial activity against Staphylococcus aureus (MIC: 4 μg/ml), various clinically isolated strains of MRSA (MIC: 4-16 μg/ml) and Acinetobacter baumannii (MIC: 4 μg/ml) when combined with subinhibitory concentrations of colistin B. Compound 12 (20 mg/kg) yielded mild improvement in survival of methicillin-resistant Staphylococcus aureus (MRSA)-infected mice. Additionally, enzyme inhibition tests showed that compound 12 exhibited inhibitory effects against S. aureus dihydrofolate reductase (105.1 μg/ml) and DNA gyrase (122.8 μg/ml). Compound 12 is a promising antibacterial candidate for further development.

Pyrazole-based analogs as potential antibacterial agents against methicillin-resistance staphylococcus aureus (MRSA) and its SAR elucidation

Methicillin-resistant Staphylococcus aureus (MRSA) is becoming lethal to humanity due to easy transmission and difficult-to-treat skin and flimsy diseases. The most threatening aspect is the rapid resistance development of MRSA to any approved antibiotics, including vancomycin. The development of new, efficient, and nontoxic drug candidate to fight against MRSA isolates is the need of the hour. The intriguing molecular structure and versatile bioactive pyrazole core attracting to development required novel antibiotics. This review presents the decade developments of pyrazole-containing derivatives with a broad antibacterial movement against diverged bacterial strains. In specific, we correlated the efficacy of structurally diversified pyrazole analogs against MRSA and discussed different angles of structure-activity relationship (SAR). The current survey highlights pyrazole hybrids' present scenario on MRSA studies, covering articles published from 2011 to 2020. This collective information may become an excellent platform to plan and develop new pyrazole-based small MRSA growth inhibitors with minimal side effects.

A Celecoxib Derivative Eradicates Antibiotic-Resistant Staphylococcus aureus and Biofilms by Targeting YidC2 Translocase

The treatment of Staphylococcus aureus infections is impeded by the prevalence of MRSA and the formation of persisters and biofilms. Previously, we identified two celecoxib derivatives, Cpd36 and Cpd46, to eradicate MRSA and other staphylococci. Through whole-genome resequencing, we obtained several lines of evidence that these compounds might act by targeting the membrane protein translocase YidC2. Our data showed that ectopic expression of YidC2 in S. aureus decreased the bacterial susceptibility to Cpd36 and Cpd46, and that the YidC2-mediated tolerance to environmental stresses was suppressed by both compounds. Moreover, the membrane translocation of ATP synthase subunit c, a substrate of YidC2, was blocked by Cpd46, leading to a reduction in bacterial ATP production. Furthermore, we found that the thermal stability of bacterial YidC2 was enhanced, and introducing point mutations into the substrate-interacting cavity of YidC2 had a dramatic effect on Cpd36 binding via surface plasmon resonance assays. Finally, we demonstrated that these YidC2 inhibitors could effectively eradicate MRSA persisters and biofilms. Our findings highlight the potential of impeding YidC2-mediated translocation of membrane proteins as a new strategy for the treatment of bacterial infections.

Development of celecoxib-derived antifungals for crop protection

Selective COX-2 inhibitor celecoxib was found directly inhibiting the growth of tested phytopathogenic fungi with the inhibitory rate ranging from 30 to 40% at 100 µg/ml. Lead optimization of celecoxib led to the identification of compound 12 among its derivatives as the most active antifungal candidate. The antifungal effect of compound 12 was supposed to be independent of COX-2 inhibition. Transcriptome profiling analysis of Fusarium graminearium (PH-1) treated with compound 12 brought about 406 up-regulated and 572 down-regulated differentially express genes (DEGs) respectively.

Identification of Small-Molecule Inhibitors of Brucella Diaminopimelate Decarboxylase by Using a High-Throughput Screening Assay

Brucellosis, caused by intracellular gram-negative pathogens of the genus Brucella, continues to be one of the most pandemic zoonotic diseases in most countries. At present, the therapeutic treatment of brucellosis relies on a combination of multiple antibiotics that involves a long course of treatment, easy relapse, and high side effects from the use of certain antibiotics (such as streptomycin). Thus, the need to identify novel drugs or targets to control this disease is urgent. Diaminopimelate decarboxylase (DAPDC), a key enzyme involved in the bacterial diaminopimelate (DAP) biosynthetic pathway, was suggested to be a promising anti-Brucella target in our previous study. In this work, the biological activity of Brucella melitensis DAPDC was characterized, and a library of 1,591 compounds was screened for inhibitors of DAPDC. The results of a high-throughput screening (HTS) assay showed that 24 compounds inhibited DAPDC activity. In a further in vitro bacterial inhibition experiment, five compounds exhibited anti-Brucella activity (SID3, SID4, SID14, SID15, and SID20). These results suggested that the identified compounds can be used as potent molecules against brucellosis and that the application ranges of these approved drugs can be expanded in the future.

1,2-Addition to trifluoromethylated β-enamino diketones: regioselective synthesis of trifluoromethyl-containing azomethine pyrazoles and isoxazoles

Trifluoromethylated β-enamino diketones undergo type 1,2-addition leading to regioselective synthesis of trifluoromethylated azoles containing an azomethine group.

Celecoxib potentiates antibiotic uptake by altering membrane potential and permeability in Staphylococcus aureus

Background

We have shown previously that celecoxib enhances the antibacterial effect of antibiotics and has sensitized drug-resistant bacteria to antibiotics at low concentrations using in vitro and in vivo model systems and also using clinically isolated ESKAPE pathogens.

Objectives

To identify the mechanism of action of celecoxib in potentiating the effect of antibiotics on bacteria.

Methods

Toxicogenomic expression analysis of Staphylococcus aureus in the presence or absence of ampicillin, celecoxib or both was carried out by microarray followed by validation of microarray results by flow cytometry and real-time PCR analysis, cocrystal development and analysis.

Results

The RNA expression map clearly indicated a change in the global transcriptome of S. aureus in the presence of cells treated with ampicillin alone, which was similar to that of celecoxib-treated cells in co-treated cells. Several essential, non-essential and virulence genes such as α-haemolysin (HLA), enterotoxins and β-lactamase were differentially regulated in co-treated cells. Further detailed analysis of the expression data indicated that the ion transporters and enzymes of the lipid biosynthesis pathway were down-regulated in co-treated cells leading to decreased membrane permeability and membrane potential. Cocrystal studies using Powder-X-Ray Diffraction (PXRD) and differential scanning calorimetry (DSC) indicated interactions between celecoxib and ampicillin, which might help in the entry of antibiotics.

Conclusions

Although further studies are warranted, here we report that celecoxib alters membrane potential and permeability, specifically by affecting the Na+/K+ ion transporter, and thereby increases the uptake of ampicillin by S. aureus.

AR-13, a Celecoxib Derivative, Directly Kills Francisella In Vitro and Aids Clearance and Mouse Survival In Vivo

Francisella tularensis (F. tularensis) is the causative agent of tularemia and is classified as a Tier 1 select agent. No licensed vaccine is currently available in the United States and treatment of tularemia is confined to few antibiotics. In this study, we demonstrate that AR-13, a derivative of the cyclooxygenase-2 inhibitor celecoxib, exhibits direct in vitro bactericidal killing activity against Francisella including a type A strain of F. tularensis (SchuS4) and the live vaccine strain (LVS), as well as toward the intracellular proliferation of LVS in macrophages, without causing significant host cell toxicity. Identification of an AR-13-resistant isolate indicates that this compound has an intracellular target(s) and that efflux pumps can mediate AR-13 resistance. In the mouse model of tularemia, AR-13 treatment protected 50% of the mice from lethal LVS infection and prolonged survival time from a lethal dose of F. tularensis SchuS4. Combination of AR-13 with a sub-optimal dose of gentamicin protected 60% of F. tularensis SchuS4-infected mice from death. Taken together, these data support the translational potential of AR-13 as a lead compound for the further development of new anti-Francisella agents.

Bacterial Networks on Hydrophobic Micropillars

Bacteria have evolved as intelligent microorganisms that can colonize and form highly structured and cooperative multicellular communities with sophisticated singular and collective behaviors. The initial stages of colony formation and intercellular communication are particularly important to understand and depend highly on the spatial organization of cells. Controlling the distribution and growth of bacterial cells at the nanoscale is, therefore, of great interest in understanding the mechanisms of cell-cell communication at the initial stages of colony formation. Staphyloccocus aureus, a ubiquitous human pathogen, is of specific clinical importance due to the rise of antibiotic resistant strains of this species, which can cause life-threatening infections. Although several methods have attempted to pattern bacterial cells onto solid surfaces at single cell resolution, no study has truly controlled the 3D architectures of growing colonies. Herein, we present a simple, low-cost method to pattern S. aureus bacterial colonies and control the architecture of their growth. Using the wetting properties of micropatterened poly(dimethyl siloxane) platforms, with help from the physiological activities of the S. aureus cells, we fabricated connected networks of bacterial microcolonies of various sizes. Unlike conventional heterogeneous growth of biofilms on surfaces, the patterned S. aureus microcolonies in this work grow radially from nanostrings of a few bacterial cells, to form micrometer-thick rods when provided with a nutrient rich environment. This simple, efficient, and low-cost method can be used as a platform for studies of cell-cell communication phenomena, such as quorum sensing, horizontal gene transfer, and metabolic cross-feeding especially during initial stages of colony formation.

Structure-activity relationships and optimization of acyclic acylphloroglucinol analogues as novel antimicrobial agents

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious threat to global public health, because it exhibits resistance to existing antibiotics and therefore high rates of morbidity and mortality. In this study, twenty-one natural product-based acylphloroglucinol congeners were synthesized, which possessed different side chains. Antibacterial screening against MRSA strains revealed that acyl moiety tailoring is a prerequisite for the antibacterial activity. Moreover, the lipophilicity, rather than the magnitude of the hydrophobic acyl tail dominates variability in activity potency. Compound 11j was identified as a promising lead for the generation of new anti-MRSA drug development. It was discovered by optimization of the side chain length in light of the potency, the breadth of the antibacterial spectrum, the rate of bactericidal action, as well as the membrane selectivity. Compound 11j exerted profound in vitro antibacterial activity against the MRSA strain (JCSC 2172), and its MIC was 3-4 orders of magnitude lower than that of vancomycin. A preliminary mode of action study of compound 11j at the biophysical and morphology levels disclosed that the mechanism underlying its anti-MRSA activity included membrane depolarization and, to a lesser extent, membrane disruption and cell lysis.

In vitro and in vivo activity of a novel sorafenib derivative SC5005 against MRSA

OBJECTIVES

The emergence of MRSA strains resistant to most antibiotics is a serious threat to public health. Based on our discovery that the tyrosine kinase inhibitor sorafenib exhibits inhibitory activity against Staphylococcus species, the objective of this study is to exploit this unique antibacterial activity of sorafenib to develop novel antibacterial agents against MRSA.

METHODS

A sorafenib-based focused compound library was synthesized by substituting the pyridinyl and phenyl groups with different functional groups. The resulting sorafenib derivatives were screened for growth-suppressive activities against Staphylococcus aureus and Staphylococcus epidermidis following CLSI guidelines and for cytotoxicity towards human cells using MTT cell viability assays. Compounds with high selectivity for bacterial inhibition over cytotoxicity were further evaluated by time-kill assay and Caenorhabditis elegans and mice survival assays to evaluate their efficacy in vitro and in vivo.

RESULTS

The screening of sorafenib derivatives led to the identification of compound SC5005 as a lead compound with high potency in killing different clinical strains of MRSA with an MIC90 of 0.5 mg/L and with low cytotoxicity, as demonstrated by IC50-to-MIC ratios of up to 40. In addition, SC5005 showed a significant protective effect in MSSA- or MRSA-infected C. elegans. Intraperitoneal administration of SC5005 at 10 mg/kg significantly improved the survival of MRSA-infected C57BL/6 mice.

CONCLUSIONS

In light of its high potency in suppressing MRSA in both in vitro and in vivo models, SC5005 represents a potential lead agent for continued preclinical development as a therapeutic intervention against MRSA.

Repurposing celecoxib as a topical antimicrobial agent

There is an urgent need for new antibiotics and alternative strategies to combat multidrug-resistant bacterial pathogens, which are a growing clinical issue. Repurposing existing approved drugs with known pharmacology and toxicology is an alternative strategy to accelerate antimicrobial research and development. In this study, we show that celecoxib, a marketed inhibitor of cyclooxygenase-2, exhibits broad-spectrum antimicrobial activity against Gram-positive pathogens from a variety of genera, including Staphylococcus, Streptococcus, Listeria, Bacillus, and Mycobacterium, but not against Gram-negative pathogens. However, celecoxib is active against all of the Gram-negative bacteria tested, including strains of, Acinetobacter, and Pseudomonas, when their intrinsic resistance is artificially compromised by outer membrane permeabilizing agents such as colistin. The effect of celecoxib on incorporation of radioactive precursors into macromolecules in Staphylococcus aureus was examined. The primary antimicrobial mechanism of action of celecoxib was the dose-dependent inhibition of RNA, DNA, and protein synthesis. Further, we demonstrate the in vivo efficacy of celecoxib in a methicillin-resistant S. aureus (MRSA) infected Caenorhabditis elegans whole animal model. Topical application of celecoxib (1 and 2%) significantly reduced the mean bacterial count in a mouse model of MRSA skin infection. Further, celecoxib decreased the levels of all inflammatory cytokines tested, including tumor necrosis factor-α, interleukin-6, interleukin-1 beta, and monocyte chemo attractant protein-1 in wounds caused by MRSA infection. Celecoxib also exhibited synergy with many conventional antimicrobials when tested against four clinical isolates of S. aureus. Collectively, these results demonstrate that celecoxib alone, or in combination with traditional antimicrobials, has a potential to use as a topical drug for the treatment of bacterial skin infections.

Metal-Based Antibacterial Substrates for Biomedical Applications

The interest in nanotechnology and the growing concern for the antibiotic resistance demonstrated by many microorganisms have recently stimulated many efforts in designing innovative biomaterials and substrates with antibacterial properties. Among the implemented strategies to control the incidence of infections associated with the use of biomedical device and implants, interesting routes are represented by the incorporation of bactericidal agents onto the surface of biomaterials for the prevention of bacterial adhesion and biofilm growth. Natural products and particularly bioactive metals such as silver, copper and zinc represent an interesting alternative for the development of advanced biomaterials with antimicrobial properties. This review presents an overview of recent progress in the modification of biomaterials as well as the most attractive techniques for the deposition of antimicrobial coatings on different substrates for biomedical application. Moreover, some research activities and results achieved by the authors in the development of antibacterial materials are also presented and discussed.

Design and synthesis of novel anti-tuberculosis agents from the celecoxib pharmacophore

The identification of compounds with anti-mycobacterial activity within classes of molecules that have been developed for other purposes is a fruitful approach for the development of anti-tuberculosis (TB) agents. In this study we used the scaffold of celecoxib which exhibits several activities against different pathogens, for the design and focused synthesis of a library of 64 compounds. For the primary screen, we used a bioluminescence-based method by constructing a luciferase-expressing reporter M.tb strain which contains the entire bacterial Lux operon cloned in a mycobacterial integrative expression vector. Through the screening of this library, we identified 6 hit compounds with high in vitro anti-mycobacterial activity (IC₅₀ ∼0.18-0.48 μM). In particular, compounds 41, 51 and 53 were capable of inhibiting M.tb as effectively as the anti-TB drug isoniazid (INH) at 5 μM over a 72-h period, as analyzed by both bioluminescence- and colony forming unit (CFU)-based assays. All hit compounds also showed anti-M.tb activities against several multi-drug-resistant (MDR) strains. Most of the hit compounds showed no cytotoxicity for human macrophages at concentrations as high as 40 μM, setting the stage for further optimization and development of these anti-TB hit compounds both ex vivo and in vivo.

Responses of Staphylococcus aureus bacterial cells to nanocrystalline nickel nanostructures

A broad range of human diseases are associated with bacterial infections, often initiated by specific adhesion of a bacterium to the target environment. Despite the significant role of bacterial adhesion in human infectious diseases, details and mechanisms of bacterial adhesion have remained elusive. Herein, we study the physical interactions between Staphylococcus aureus, a type of micro-organism relevant to infections associated with medical implants, and nanocrystalline (nc) nickel nanostructures with various columnar features, including solid core, hollow, x-shaped and c-shaped pillars. Scanning electron microscopy results show the tendency of these bacterial cells to attach to the nickel nanostructures. Moreover, unique single bacterium attachment characteristics were observed on nickel nanostructures with dimensions comparable to the size of a single bacterium.

Delivery of host cell-directed therapeutics for intracellular pathogen clearance

Intracellular pathogens present a major health risk because of their innate ability to evade clearance. Their location within host cells and ability to react to the host environment by mutation or transcriptional changes often enables survival mechanisms to resist standard therapies. Host-directed drugs do not target the pathogen, minimizing the potential development of drug resistance; however, they can be difficult to deliver efficiently to intracellular sites. Vehicle delivery of host-mediated response drugs not only improves drug distribution and toxicity profiles, but can reduce the total amount of drug necessary to clear infection. In this article, we will review some host-directed drugs and current drug delivery techniques that can be used to efficiently clear intracellular infections.

Advances in MRSA drug discovery: where are we and where do we need to be?

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) have been on the increase during the past decade, due to the steady growth of the elderly and immunocompromised patients, and the emergence of multidrug-resistant (MDR) bacterial strains. Although there are a limited number of anti-MRSA drugs available, a number of different combination antimicrobial drug regimens have been used to treat serious MRSA infections. Thus, the addition of several new antistaphylococcal drugs into clinical practice should broaden clinician's therapeutic options. As MRSA is one of the most common and problematic bacteria associated with increasing antimicrobial resistance, continuous efforts for the discovery of lead compounds as well as development of alternative therapies and faster diagnostics are required.

AREAS COVERED

This article summarizes the FDA-approved drugs to treat MRSA infections, the drugs in clinical trials, and the drug leads for MRSA and related Gram-positive bacterial infections. In addition, the article discusses the mode of action of antistaphylococcal molecules and the resistant mechanisms of some molecules.

EXPERT OPINION

The number of pipeline drugs presently undergoing clinical trials is not particularly encouraging. There are limited and rather expensive therapeutic options for MRSA infections in the critically ill. Further research efforts are required for effective phage therapy on MRSA infections in clinical use, which seem to be attractive therapeutic options for the future.