The millennium bugs--the need for and development of new antibacterials

Using tea nanoclusters as β-lactamase inhibitors to cure multidrug-resistant bacterial pneumonia: A promising therapeutic strategy by Chinese materioherbology

β-lactamase, a kind of hydrolase in multi-drug resistant pathogens, can hydrolyze β-lactam antibiotics and make these kinds of antibiotics invalid. Small-molecular inhibitors about the enzyme and their mechanism are widely investigated but they may result in unavoidable adverse reactions and drug-resistance. Herein, we propose a new therapeutic strategy of Chinese materioherbology, in which herbal medicine or traditional Chinese medicinal herbs can be employed as biological functional materials or refreshed/excited by means of materialogy. Natural tea nanoclusters (TNCs) were extracted from tea to inhibit β-lactamase. Different from the mechanism of small-molecular inhibitors inhibiting enzymes by binding to the corresponding active sites, the TNCs as a cap cover the protein pocket and create a spatial barrier between the active sites and antibiotics, which was named "capping-pocket" effect. TNCs were combined with amoxicillin sodium (Amo) to treat the methicillin-resistant Staphylococcus aureus (MRSA) pneumonia in mice. This combinatorial therapy remarkably outperforms antibiotic monotherapy in reducing MRSA infections and the associated inflammation in mice. The therapeutic strategy exhibited excellent biosafety, without any side effects, even in piglets. Hence, TNCs have great clinical value in potentiating β-lactam antibiotic activity for combatting multi-drug resistant pathogen infections and the "pocket capping" effect can guide the design of new enzyme inhibitors in near future.

Influence of chlorine and methyl substituents and their position on the antimicrobial activities and crystal structures of 4-methyl-1,6-diphenylpyrimidine-2(1H)-selenone derivatives

Derivatives of 4-methyl-1,6-diphenylpyrimidine-2(1H)-selenone show very strong antimicrobial activity. In order to extend the current knowledge about the features responsible for the biological activity, crystal structure analyses are presented for 4-methyl-1-(2-methylphenyl)-6-phenylpyrimidine-2(1H)-selenone (1), 4-methyl-1-(3-methylphenyl)-6-phenylpyrimidine-2(1H)-selenone (2), 4-methyl-1-(4-methylphenyl)-6-phenylpyrimidine-2(1H)-selenone (3) (all C₁₈H₁₆N₂Se) and 1-(4-chlorophenyl)-4-methyl-6-phenylpyrimidine-2(1H)-selenone (4) (C₁₇H₁₃ClN₂Se). Furthermore, the antibacterial and antifungal activities of these compounds were evaluated. All the presented derivatives crystallize in the space group P2₁/c with one molecule in the asymmetric unit. The molecular geometries differ slightly in the mutual orientation of the rings. The packing of molecules in the crystals is dominated by C-H...N and C-H...Se intermolecular interactions. Additionally, in the crystal structure of 4, C-H...Cl intermolecular interactions are observed. The introduction of a methyl or chlorine substituent improves the biological activity, while its position significantly affects biological activity only in case of the chlorine substituent.

Challenges and New Therapeutic Approaches in the Management of Chronic Wounds

Chronic non-healing wounds are estimated to cost the US healthcare $28-$31 billion per year. Diabetic ulcers, arterial and venous ulcers, and pressure ulcers are some of the most common types of chronic wounds. The burden of chronic wounds continues to rise due to the current epidemic of obesity and diabetes and the increase in elderly adults in the population who are more vulnerable to chronic wounds than younger individuals. This patient population is also highly vulnerable to debilitating infections caused by opportunistic and multi-drug resistant pathogens. Reduced microcirculation, decreased availability of cytokines and growth factors that promote wound closure and healing, and infections by multi-drug resistant and biofilm forming microbes are some of the critical factors that contribute to the development of chronic non-healing wounds. This review discusses novel approaches to understand chronic wound pathology and methods to improve chronic wound care, particularly when chronic wounds are infected by multi-drug resistant, biofilm forming microbes.

Synthesis and molecular docking studies of some novel antimicrobial benzamides

Common use of classical antibiotics has caused to the growing emergence of many resistant strains of pathogenic bacteria. Therefore, we aimed to synthesize a number of N-(2-hydroxy-(4 or 5)-nitrophenyl)benzamide derivatives as a new class of antimicrobial compounds. Moreover, our second goal is to predict the interaction between active structures and enzymes (DNA -gyrase and FtsA) in the binding mode. In this study, thirteen N-(2-hydroxy-(4 or 5-nitrophenyl)-substituted-benzamides were synthesized and determined for their antimicrobial activity using the microdilution method. According to this work, none of the compounds showed any activity against Candida albicans and its clinical isolate. Some of the benzamides (4N1, 5N1, 5N2) displayed very significant activity against Staphylococcus aureus and MSSA with <4 µg/ml MIC value, even they were found to be more potent than ceftazidime. 4N1 was also found to be more effective than gentamicin against Enterococcus faecalis clinical isolate. Molecular docking studies revealed that 4N1, 5N1, and 5N2 showed a good interactions with DNA-gyrase. Moreover, 5N1 has interacted with FtsA enzyme in the binding mode, as well. Only compound 5N4 displayed very good activity against Escherichia coli ATCC 25922. These findings showed us that 4N1, 5N1, 5N2, and 5N4 could be lead compounds to discover new antibacterial candidates against multidrug-resistant strains.

Coral and Coral-Associated Microorganisms: A Prolific Source of Potential Bioactive Natural Products

Marine invertebrates and their associated microorganisms are rich sources of bioactive compounds. Among them, coral and its associated microorganisms are promising providers of marine bioactive compounds. The present review provides an overview of bioactive compounds that are produced by corals and coral-associated microorganisms, covering the literature from 2010 to March 2019. Accordingly, 245 natural products that possess a wide range of potent bioactivities, such as anti-inflammatory, cytotoxic, antimicrobial, antivirus, and antifouling activities, among others, are described in this review.

Coral and Coral-Associated Microorganisms: A Prolific Source of Potential Bioactive Natural Products

Marine invertebrates and their associated microorganisms are rich sources of bioactive compounds. Among them, coral and its associated microorganisms are promising providers of marine bioactive compounds. The present review provides an overview of bioactive compounds that are produced by corals and coral-associated microorganisms, covering the literature from 2010 to March 2019. Accordingly, 245 natural products that possess a wide range of potent bioactivities, such as anti-inflammatory, cytotoxic, antimicrobial, antivirus, and antifouling activities, among others, are described in this review.

Advances in Antarctic Research for Antimicrobial Discovery: A Comprehensive Narrative Review of Bacteria from Antarctic Environments as Potential Sources of Novel Antibiotic Compounds Against Human Pathogens and Microorganisms of Industrial Importance

The recent emergence of antibiotic-resistant bacteria has become a critical public health problem. It is also a concern for industries, since multidrug-resistant microorganisms affect the production of many agricultural and food products of economic importance. Therefore, discovering new antibiotics is crucial for controlling pathogens in both clinical and industrial spheres. Most antibiotics have resulted from bioprospecting in natural environments. Today, however, the chances of making novel discoveries of bioactive molecules from various well-known sources have dramatically diminished. Consequently, unexplored and unique environments have become more likely avenues for discovering novel antimicrobial metabolites from bacteria. Due to their extreme polar environment, Antarctic bacteria in particular have been reported as a potential source for new antimicrobial compounds. We conducted a narrative review of the literature about findings relating to the production of antimicrobial compounds by Antarctic bacteria, showing how bacterial adaptation to extreme Antarctic conditions confers the ability to produce these compounds. We highlighted the diversity of antibiotic-producing Antarctic microorganisms, including the phyla Proteobacteria, Actinobacteria, Cyanobacteria, Firmicutes, and Bacteroidetes, which has led to the identification of new antibiotic molecules and supports the belief that research on Antarctic bacterial strains has important potential for biotechnology applications, while providing a better understanding of polar ecosystems.

A comparative study of phytoconstituents and antibacterial activity of in vitro derived materials of four Passiflora species

Passiflora species are well known for their common use in popular medicine for the treatment of several diseases, such as insomnia, anxiety, and hysteria, in addition to their anti-inflammatory, antioxidant, analgesic and antibacterial potential. However, few data about the chemical composition and the medicinal potential of in vitro derived materials are available. Therefore, the goal of this work was to compare, for the first time, the phytoconstituents of in vitro derived materials of four Passiflora species, and evaluate the antibacterial potential of their extracts against 20 Gram-positive and negative strains. Chromatographic analysis indicated the presence of saponins in roots extracts from all studied species, whereas leaf extracts presented both saponins and flavonoids. Extracts from leaves and roots of P. alata and P. foetida exhibited a selective inhibitory activity against B. thuringiensis and S. pyogenes, which might be related to the presence of a high concentration of secondary metabolites, including flavonoids and saponins.

Anti-Quorum Sensing Natural Compounds

Increasing extent of pathogenic resistance to drugs has encouraged the seeking for new anti-virulence drugs. Many pharmacological and pharmacognostical researches are performed to identify new drugs or discover new structures for the development of novel therapeutic agents in the antibiotic treatments. Although many phytochemicals show prominent antimicrobial activity, their power lies in their anti-virulence properties. Quorum sensing (QS) is a bacterial intercellular communication mechanism, which depends on bacterial cell population density and controls the pathogenesis of many organisms by regulating gene expression, including virulence determinants. QS has become an attractive target for the development of novel anti-infective agents that do not rely on the use of antibiotics. Anti-QS compounds are known to have the ability to prohibit bacterial pathogenicity. Medicinal plants offer an attractive repertoire of phytochemicals with novel microbial disease-controlling potential, due to the spectrum of secondary metabolites present in extracts, which include phenolics, quinones, flavonoids, alkaloids, terpenoids, and polyacetylenes. They have recently received considerable attention as a new source of safe and effective QS inhibitory substances. The objective of this review is to give a brief account of the research reports on the plants and natural compounds with anti-QS potential.

Synthesis, Antimicrobial, and Computational Evaluation of Novel Isobutylchalcones as Antimicrobial Agents

A series of 25 new chalcones were synthesized by Claisen-Schmidt condensation, well characterized by spectroscopic data, and evaluated for their antibacterial and antifungal activities by serial tube dilution method. Among the compounds tested, A3 and A6 containing 2,4-dichlorophenyl and 2,4-difluorophenyl moiety, respectively, were found to be the most potent in the series against both bacterial and fungal strains with a MIC value of 16 µg/mL in each case. Further computational evaluation for antimicrobial activity was performed by atom based 3D-QSAR using PHASE™ software in order to have a correlation between the observed activities and predicted activities. The computational studies were in agreement with the in vitro antimicrobial results and had identified the most promising chalcones as antimicrobial agents and the responsible structural features for the proposed activity.

Antimicrobial Activity of Ceftolozane-Tazobactam Tested Against Enterobacteriaceae and Pseudomonas aeruginosa with Various Resistance Patterns Isolated in U.S. Hospitals (2013-2016) as Part of the Surveillance Program: Program to Assess Ceftolozane-Tazobactam Susceptibility

This study evaluated the in vitro activity of ceftolozane-tazobactam and comparator agents tested against Enterobacteriaceae and Pseudomonas aeruginosa isolates from hospitalized patients in the United States. Ceftolozane-tazobactam is an antipseudomonal cephalosporin combined with a well-established β-lactamase inhibitor. A total of 18,960 organisms (15,223 Enterobacteriaceae and 3,737 P. aeruginosa) were consecutively collected from 32 medical centers located in all nine U.S. census divisions from 2013 to 2016. Organisms were tested for susceptibility by broth microdilution. CLSI and EUCAST interpretive criteria were used. Ceftolozane-tazobactam (94.4% susceptible), amikacin (99.0% susceptible), and meropenem (98.0% susceptible) were the most active compounds tested against Enterobacteriaceae. Among the Enterobacteriaceae isolates tested, 1.9% (n = 286) were carbapenem-resistant Enterobacteriaceae (CRE) and 9.5% (n = 1,450) exhibited an extended-spectrum β-lactamase (ESBL) non-CRE phenotype. Although ceftolozane-tazobactam showed good activity against ESBL non-CRE phenotype strains of Enterobacteriaceae (87.5% susceptible), it lacked useful activity against CRE. Ceftolozane-tazobactam was the most potent β-lactam agent tested against P. aeruginosa isolates, with 97.3% susceptible. Only colistin was more active, inhibiting 99.5% of isolates. Ceftolozane-tazobactam also maintained good activity against multidrug-resistant P. aeruginosa, with 88.6% susceptible. Ceftolozane-tazobactam was the most active β-lactam agent tested against P. aeruginosa and was more active than available cephalosporins and piperacillin-tazobactam against Enterobacteriaceae.

Synthesis, antimicrobial activity and toxicity to nematodes of cyclam derivatives

The antimicrobial activity and toxicity to nematodes of the cyclam salt [H₂{H₂(^4-CF₃PhCH₂)₂Cyclam}](CH₃COO)₂⋅(CH₃COOH)₂ were evaluated. Estimated minimum inhibitory concentrations (MICs) of 9, 261 and 15 µg/mL were obtained for Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, respectively. For selected Candida spp., the estimated MICs obtained ranged from 32 µg/mL to 63 µg/mL. Bactericidal activity was demonstrated but the compound was not reliably fungicidal. Concentrations of the cyclam salt up to 32 µg/mL did not significantly affect survival of the nematode Caenorhabditis elegans; however, concentrations equal or above this value significantly affected nematode survival in a dose-dependent manner.

Phytochemical Analysis, Identification and Quantification of Antibacterial Active Compounds in Betel Leaves, Piper betle Methanolic Extract

BACKGROUND AND OBJECTIVE

The problems of bacterial diseases in aquaculture are primarily controlled by antibiotics. Medicinal plants and herbs which are seemed to be candidates of replacements for conventional antibiotics have therefore gained increasing interest. Current study was performed to investigate the presence of phytochemical constituents, antibacterial activities and composition of antibacterial active compounds in methanolic extract of local herb, Piper betle .

METHODOLOGY

Qualitative phytochemical analysis was firstly carried out to determine the possible active compounds in P. betle leaves methanolic extract. The antibacterial activities of major compounds from this extract against nine fish pathogenic bacteria were then assessed using TLC-bioautography agar overlay assay and their quantity were determined simultaneously by HPLC method.

RESULTS

The use of methanol has proved to be successful in extracting numerous bioactive compounds including antibacterial compounds. The TLC-bioautography assay revealed the inhibitory action of two compounds which were identified as hydroxychavicol and eugenol. The $-caryophyllene however was totally inactive against all the tested bacterial species. In this study, the concentration of hydroxychavicol in extract was found to be 374.72±2.79 mg g-1, while eugenol was 49.67±0.16 mg g-1.

CONCLUSION

Based on these findings, it could be concluded that hydroxychavicol and eugenol were the responsible compounds for the promising antibacterial activity of P. betle leaves methanolic extract. This inhibitory action has significantly correlated with the amount of the compounds in extract. Due to its potential, the extract of P. betle leaves or it compounds can be alternative source of potent natural antibacterial agents for aquaculture disease management.

Antibacterial activity of curcumin via apoptosis-like response in Escherichia coli

Curcumin, a naturally occurring phenolic compound, has been shown to exhibit antimicrobial activity against Candida albicans, Escherichia coli, Pseudomonas aeruginosa, etc., but the mechanism remains unclear. The present study was designed to investigate the novel antibacterial mechanism of curcumin that shows an apoptosis-like response in E. coli. We found that curcumin induces membrane damage at relatively high concentrations, but there was no effect at the minimum inhibitory concentration (MIC). At the MIC, curcumin-treated cells displayed various apoptotic markers such as reactive oxygen species (ROS) accumulation, membrane depolarization, and Ca(2+) influx. Expression of RecA protein, which mediates a bacterial apoptosis-like response, was also increased by curcumin. In order to evaluate the influence of RecA on the appearance of other apoptotic markers, phosphatidylserine (PS) exposure and DNA fragmentation were examined and compared with a RecA deletion strain (ΔRecA). These markers were detected in E. coli wild-type cells, but not in ΔRecA cells. In conclusion, our data demonstrate that curcumin induces an apoptosis-like response in E. coli that involves RecA.

Using adjuvants and environmental factors to modulate the activity of antimicrobial peptides

The increase in antibiotic resistant and multi-drug resistant bacterial infections has serious implications for the future of health care. The difficulty in finding both new microbial targets and new drugs against existing targets adds to the concern. The use of combination and adjuvant therapies are potential strategies to counter this threat. Antimicrobial peptides (AMPs) are a promising class of antibiotics (ABs), particularly for topical and surface applications. Efforts have been directed toward a number of strategies, including the use of conventional ABs combined with AMPs, and the use of potentiating agents to increase the performance of AMPs. This review focuses on combination strategies such as adjuvants and the manipulation of environmental variables to improve the efficacy of AMPs as potential therapeutic agents. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Discovery of a potent enoyl-acyl carrier protein reductase (FabI) inhibitor suitable for antistaphylococcal agent

We report the discovery, synthesis, and biological activities of phenoxy-4-pyrone and phenoxy-4-pyridone derivatives as novel inhibitors of enoyl-acyl carrier protein reductase (FabI). Pyridone derivatives showed better activities than pyrone derivatives against FabI and Staphylococcus aureus strains, including methicillin-resistant Staphylococcus aureus (MRSA). Among the pyridone derivatives, compound 16l especially exhibited promising activities against the MRSA strain and good pharmacokinetic profiles.

Suppression of Virulence of Toxigenic Vibrio cholerae by Anethole through the Cyclic AMP (cAMP)-cAMP Receptor Protein Signaling System

Use of natural compounds as antivirulence drugs could be an alternative therapeutic approach to modify the outcome of bacterial infections, particularly in view of growing resistance to available antimicrobials. Here, we show that sub-bactericidal concentration of anethole, a component of sweet fennel seed, could suppress virulence potential in O1 El Tor biotype strains of toxigenic Vibrio cholerae, the causative agent of the ongoing 7^th cholera pandemic. The expression of cholera toxin (CT) and toxin coregulated pilus (TCP), the major virulence factors of V. cholerae, is controlled through a regulatory cascade involving activation of ToxT with synergistic coupling interaction of ToxR/ToxS with TcpP/TcpH. We present evidence that anethole inhibits in vitro expression of CT and TCP in a toxT-dependent but toxR/toxS-independent manner and through repression of tcpP/tcpH, by using bead-ELISA, western blotting and quantitative real-time RT-PCR assays. The cyclic AMP (cAMP)-cAMP receptor protein (CRP) is a well-studied global signaling system in bacterial pathogens, and this complex is known to suppress expression of tcpP/tcpH in V. cholerae. We find that anethole influences the virulence regulatory cascade by over-expressing cyaA and crp genes. Moreover, suppression of toxigenic V. cholerae-mediated fluid accumulation in ligated ileum of rabbit by anethole demonstrates its potentiality as an antivirulence drug candidate against the diseases caused by toxigenic V. cholerae. Taken altogether, these results revealing a mechanism of virulence inhibition in V. cholerae by the natural compound anethole, may have relevance in designing antivirulence compounds, particularly against multiple antibiotic resistant bacterial pathogens.

Anethole inhibits growth of recently emerged multidrug resistant toxigenic Vibrio cholerae O1 El Tor variant strains in vitro

To search natural compounds having inhibitory effect on bacterial growth is important, particularly in view of growing multidrug resistant (MDR) strains of bacterial pathogens. Like other bacterial pathogens, MDR Vibrio cholerae, the causative agent of diarrheal disease cholera, is becoming a great concern. As an approach of searching new antimicrobial agents, here, we show that anethole, a well-studied natural component of sweet fennel and star anise seeds, could potentially inhibit the growth of MDR O1 El Tor biotype, the ongoing 7th cholera pandemic variant strains of toxigenic V. cholerae. The minimum inhibitory concentration (MIC) of anethole against diverse O1 El Tor biotype strains is evaluated as 200 µg/ml. Moreover, the effect of anethole is bactericidal and exerts rapid-killing action on V. cholerae cells. This study is the first report which demonstrates that anethole, purified from natural compound, is a potent inhibitor of growth of toxigenic V. cholerae. Our data suggest that anethole could be a potential antimicrobial drug candidate, particularly against MDR V. cholerae mediated infections.

Paracentrin 1, a synthetic antimicrobial peptide from the sea-urchin Paracentrotus lividus, interferes with staphylococcal and Pseudomonas aeruginosa biofilm formation

The rise of antibiotic-resistance as well as the reduction of investments by pharmaceutical companies in the development of new antibiotics have stimulated the investigation for alternative strategies to conventional antibiotics. Many antimicrobial peptides show a high specificity for prokaryotes and a low toxicity for eukaryotic cells and, due to their mode of action the development of resistance is considered unlikely. We recently characterized an antimicrobial peptide that was called Paracentrin 1 from the 5-kDa peptide fraction from the coelomocyte cytosol of the Paracentrotus lividus. In this study, the chemically synthesized Paracentrin 1, was tested for its antimicrobial and antibiofilm properties against reference strains of Gram positive and Gram negative. The Paracentrin 1 was active against planktonic form of staphylococcal strains (reference and isolates) and Pseudomonas aeruginosa ATCC 15442 at concentrations ranging from 12.5 to 6.2 mg/ml. The Paracentrin 1 was able to inhibit biofilm formation of staphylococcal and Pseudomonas aeruginosa strains at concentrations ranging from 3.1 to 0.75 mg/ml. We consider the tested peptide as a good starting molecule for novel synthetic derivatives with improved pharmaceutical potential.

Biomimetic interfaces based on S-layer proteins, lipid membranes and functional biomolecules

Designing and utilization of biomimetic membrane systems generated by bottom-up processes is a rapidly growing scientific and engineering field. Elucidation of the supramolecular construction principle of archaeal cell envelopes composed of S-layer stabilized lipid membranes led to new strategies for generating highly stable functional lipid membranes at meso- and macroscopic scale. In this review, we provide a state-of-the-art survey of how S-layer proteins, lipids and polymers may be used as basic building blocks for the assembly of S-layer-supported lipid membranes. These biomimetic membrane systems are distinguished by a nanopatterned fluidity, enhanced stability and longevity and, thus, provide a dedicated reconstitution matrix for membrane-active peptides and transmembrane proteins. Exciting areas in the (lab-on-a-) biochip technology are combining composite S-layer membrane systems involving specific membrane functions with the silicon world. Thus, it might become possible to create artificial noses or tongues, where many receptor proteins have to be exposed and read out simultaneously. Moreover, S-layer-coated liposomes and emulsomes copying virus envelopes constitute promising nanoformulations for the production of novel targeting, delivery, encapsulation and imaging systems.

Chemical derivatives of a small molecule deubiquitinase inhibitor have antiviral activity against several RNA viruses

Most antiviral treatment options target the invading pathogen and unavoidably encounter loss of efficacy as the pathogen mutates to overcome replication restrictions. A good strategy for circumventing drug resistance, or for pathogens without treatment options, is to target host cell proteins that are utilized by viruses during infection. The small molecule WP1130 is a selective deubiquitinase inhibitor shown previously to successfully reduce replication of noroviruses and some other RNA viruses. In this study, we screened a library of 31 small molecule derivatives of WP1130 to identify compounds that retained the broad-spectrum antiviral activity of the parent compound in vitro but exhibited improved drug-like properties, particularly increased aqueous solubility. Seventeen compounds significantly reduced murine norovirus infection in murine macrophage RAW 264.7 cells, with four causing decreases in viral titers that were similar or slightly better than WP1130 (1.9 to 2.6 log scale). Antiviral activity was observed following pre-treatment and up to 1 hour postinfection in RAW 264.7 cells as well as in primary bone marrow-derived macrophages. Treatment of the human norovirus replicon system cell line with the same four compounds also decreased levels of Norwalk virus RNA. No significant cytotoxicity was observed at the working concentration of 5 µM for all compounds tested. In addition, the WP1130 derivatives maintained their broad-spectrum antiviral activity against other RNA viruses, Sindbis virus, LaCrosse virus, encephalomyocarditis virus, and Tulane virus. Thus, altering structural characteristics of WP1130 can maintain effective broad-spectrum antiviral activity while increasing aqueous solubility.

Synthesis, Characterization, and BSA Binding Studies of Some New Benzamides Related to Schiff Base

Condensation of amine 1 with aldehyde 2 gives Schiff base, N-(4-((benzofuran-2-ylmethylene) amino)phenyl)acetamide 3. Schiff base on N-acylation with different substituted acid chlorides in the presence of triethylamine gives the corresponding benzamides, N-acetyl-N-(4-((benzofuran-2-ylmethylene)amino)phenyl)substitutedbenzamide (NABP) 5a-j. The structures of newly synthesized compounds were characterized by elemental analysis, (1)H NMR, (13)C NMR FT-IR, and mass spectral studies. Compounds 3 and 5a-j have been screened for their antimicrobial activity using the disc diffusion and minimum inhibitory concentration (MIC) method against the selected bacterial and fungal strain. Compounds 5a, 5e, 5g, and 5h were found to be more active against all tested strains. The antioxidant properties were evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide radical scavenging methods. Compounds 5i and 5j showed predominant antioxidant activities among the synthesized analogues. The interaction between NABP and bovine serum albumin (BSA) was investigated using fluorescence and ultraviolet spectroscopic techniques at 298 K under imitated physiological conditions. The results revealed that NABP caused the fluorescence quenching of BSA through a static quenching procedure. The binding constants and the number of binding sites were calculated. The binding distance between the donor (BSA) and acceptor (NABP) was determined based on Forster's theory.

Antimicrobial agent exposure and the emergence and spread of resistant microorganisms: issues associated with study design

Antibiotics are essential agents that have greatly reduced human mortality due to infectious diseases. Their use, and sometimes overuse, have increased over the past several decades in humans, veterinary medicine and agriculture. However, the emergence of resistant pathogens is becoming an increasing problem that could result in the re-emergence of infectious diseases. Antibiotic prescription in human medicine plays a key role in this phenomenon. Under selection pressure, resistance can emerge in the commensal flora of treated individuals and disseminate to others. However, even if the effects of antimicrobial use on resistance is intuitively accepted, scientific rationales are required to convince physicians, legislators and public opinion to adopt appropriate behaviours and policies. With this review, we aim to provide an overview of different epidemiological study designs that are used to study the relationship between antibiotic use and the emergence and spread of resistance, as well as highlight their main strengths and weaknesses.

Architecture and conservation of the bacterial DNA replication machinery, an underexploited drug target

New antibiotics with novel modes of action are required to combat the growing threat posed by multi-drug resistant bacteria. Over the last decade, genome sequencing and other high-throughput techniques have provided tremendous insight into the molecular processes underlying cellular functions in a wide range of bacterial species. We can now use these data to assess the degree of conservation of certain aspects of bacterial physiology, to help choose the best cellular targets for development of new broad-spectrum antibacterials.

DNA replication is a conserved and essential process, and the large number of proteins that interact to replicate DNA in bacteria are distinct from those in eukaryotes and archaea; yet none of the antibiotics in current clinical use acts directly on the replication machinery. Bacterial DNA synthesis thus appears to be an underexploited drug target. However, before this system can be targeted for drug design, it is important to understand which parts are conserved and which are not, as this will have implications for the spectrum of activity of any new inhibitors against bacterial species, as well as the potential for development of drug resistance. In this review we assess similarities and differences in replication components and mechanisms across the bacteria, highlight current progress towards the discovery of novel replication inhibitors, and suggest those aspects of the replication machinery that have the greatest potential as drug targets.

Novel inhibitors of Staphylococcus aureus virulence gene expression and biofilm formation

Staphylococcus aureus is a major human pathogen and one of the more prominent pathogens causing biofilm related infections in clinic. Antibiotic resistance in S. aureus such as methicillin resistance is approaching an epidemic level. Antibiotic resistance is widespread among major human pathogens and poses a serious problem for public health. Conventional antibiotics are either bacteriostatic or bacteriocidal, leading to strong selection for antibiotic resistant pathogens. An alternative approach of inhibiting pathogen virulence without inhibiting bacterial growth may minimize the selection pressure for resistance. In previous studies, we identified a chemical series of low molecular weight compounds capable of inhibiting group A streptococcus virulence following this alternative anti-microbial approach. In the current study, we demonstrated that two analogs of this class of novel anti-virulence compounds also inhibited virulence gene expression of S. aureus and exhibited an inhibitory effect on S. aureus biofilm formation. This class of anti-virulence compounds could be a starting point for development of novel anti-microbial agents against S. aureus.

Dihydrofolate reductase as a therapeutic target for infectious diseases: opportunities and challenges

Infectious diseases caused by parasites continue to take a massive toll on human health in the poor regions of the world. Filling the anti-infective drug-discovery pipeline has never been as challenging as it is now. The organisms responsible for these diseases have interesting biology with many potential biochemical targets. Inhibition of metabolic enzymes has been established as an attractive strategy for anti-infectious drug development. In this field, dihydrofolate reductase (DHFR) is an important enzyme in nucleic and amino acid synthesis and an extensively studied drug target over the past 50 years. The challenges for novel DHFR inhibition-based chemotherapeutics for the treatment of infectious diseases are now focused on overcoming the resistance problem as well as cost–effectiveness. Each year, the large number of literature citations attest the continued popularity of DHFR. It becomes truly the ‘enzyme of choice for all seasons and almost all reasons’. Herein, we summarize the opportunities and challenges in developing novel lead based on this target.

Pharmacophore and molecular docking guided 3D-QSAR study of bacterial enoyl-ACP reductase (FabI) Inhibitors

Enoyl acyl carrier protein (ACP) reductase (FabI) is a potential target for the development of antibacterial agents. Three-dimensional quantitative structure-activity relationships (3D-QSAR) for substituted formamides series of FabI inhibitors were investigated using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) techniques. Pharmacophore and molecular docking methods were used for construction of the molecular alignments. A training set of 36 compounds was performed to create the 3D-QSAR models and their external predictivity was proven using a test set of 11 compounds. Graphical interpretation of the results revealed important structural features of the formamides related to the active site of FabI. The results may be exploited for further optimization of the design of new potent FabI inhibitors.

Synthesis, antimicrobial activity and cytotoxicity of some new carbazole derivatives

In this work, some N-(9-Ethyl-9H-carbazole-3-yl)-2-(phenoxy)acetamide derivatives were synthesised and evaluated for their antimicrobial activity and cytotoxicity. The structural elucidation of the compounds was performed by IR, (1)H-NMR, (13)C-NMR and FAB(+)-MS spectral data and elemental analyses. The title compounds were obtained by reacting 2-chloro-N-(9-ethyl-9H-carbazole-3-yl)acetamide with some substituted phenols. The synthesised compounds were investigated for their antibacterial and antifungal activities against Micrococcus luteus, Bacillus subtilis, Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Listeria monocytogenes and Candida albicans. The compounds N-(9-Ethyl-9H-carbazole-3-yl)-2-(4-ethylphenoxy)acetamide (2c) and N-(9-Ethyl-9H-carbazole-3-yl)-2-(quinolin-8-yloxy)acetamide (2n) showed notable antimicrobial activity. The compounds were also studied for their cytotoxic effects using MTT assay, and it was seen that 2n had the lowest cytotoxic activity against NIH/3T3 cells.

Antimicrobial activity and mechanism of action of Nu-3, a protonated modified nucleotide

Background

"Nubiotics" are synthetic oligonucleotides and nucleotides with nuclease-resistant backbones, and are fully protonated for enhanced ability to be taken up by bacterial cells. Nu-3 [butyl-phosphate-5'-thymidine-3'-phosphate-butyl], one of the family members of Nubiotics was efficacious in the treatment of burn-wound infections by Pseudomonas aeruginosa in mice. Subsequent studies revealed that Nu-3 had a favorable toxicological profile for use as a pharmaceutical agent. This study evaluated the antibacterial activity of Nu-3 in vitro and its efficacy as a topical antibiotic. In addition, we investigated the possible mechanisms of Nu-3 action at the levels of DNA synthesis and bacterial membrane changes.

Methods

Antimicrobial minimum inhibitory concentrations (MIC) experiments with Nu-3 and controls were measured against a range of Gram-positive and Gram-negative bacteria, including some hospital isolates according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Analysis of the killing kinetics of Nu-3 was also performed against two strains (Staphylococcus aureus cvcc 2248 and Pseudomonas aeruginosa cvcc 5668). The mouse skin suture-wound infection model was used to evaluate the antibacterial activity of Nu-3. We used a 5-Bromo-2'-deoxy-uridine Labeling and Detection Kit III (Roche, Switzerland) to analyze DNA replication in bacteria according to the manufacturer's instruction. The BacLight™ Bacterial Membrane Potential Kit (Invitrogen) was used to measure the bacterial membrane potential in S. aureus.

Results

Nu-3 had a wide antibacterial spectrum to Gram-positive, Gram-negative and some resistant bacteria. The MIC values of Nu-3 against all tested MRSA and MSSA were roughly in a same range while MICs of Oxacillin and Vancomycin varied between the bacteria tested. In the mouse model of skin wound infection study, the treatment with 5% Nu-3 glycerine solution also showed comparable therapeutic effects to Ciprofloxacin Hydrochloride Ointment. While Nu-3 had no effect on DNA synthesis of the tested bacteria as demonstrated in a BrdU assay, it could cause bacterial cell membrane depolarization, as measured using a BacLight™ Bacterial Membrane Potential Kit.

Conclusions

These results provide additional experimental data that are consistent with the hypothesis that Nu-3 represents a new class of antibacterial agents for treating topical infections and acts via a different mechanism from conventional antibiotics.

Gram-Negative and Gram-Positive Antibacterial Properties of the Whole Plant Extract of Willow Herb (Epilobium angustifolium)

The emergence of new pathogens and the increase in the number of multidrug-resistant strains in well-established pathogens during the past decade represent a growing public health concern globally. With the current lack of research and development of new antibiotics by large pharmaceutical companies due to poor financial returns, new alternatives need to be explored including natural herbal or plant-based extracts with reported antibacterial properties. Willow herb ( Epilobium angustifolium) preparations have been used in traditional aboriginal and folk medicine preparations externally as an antiphlogistic to treat prostate and gastrointestinal disorders and as an antiseptic to treat infected wounds. The authors hypothesized that a whole plant extract of willow herb would exhibit antimicrobial properties on a variety of both Gram-positive and gram-negative bacteria in culture. The authors found that, in comparison to growth controls, willow herb extract significantly inhibited the growth of Micrococcus luteus ( p < .01), Staphylococcus aureus ( p < .05), Escherichia coli ( p < .001), and Pseudomonas aeruginosa ( p < .001). They also found that willow herb extract inhibited the growth of bacteria in culture more effectively than vancomycin ( p < .05) or tetracycline ( p < .004). These results provide preliminary support for the traditional folkloric claim that the plant willow herb possesses antibacterial properties against a variety of gram-positive and gram-negative bacteria. Given that whole plant extract was utilized for this study, further investigations are warranted to determine which specific part of the plant (i.e., leaves, stem, roots, and flowers) possess the antibacterial properties.

The heme sensing response regulator HssR in Staphylococcus aureus but not the homologous RR23 in Listeria monocytogenes modulates susceptibility to the antimicrobial peptide plectasin

Background

Host defence peptides (HDPs), also known as antimicrobial peptides (AMPs), have emerged as potential new therapeutics and their antimicrobial spectrum covers a wide range of target organisms. However, the mode of action and the genetics behind the bacterial response to HDPs is incompletely understood and such knowledge is required to evaluate their potential as antimicrobial therapeutics. Plectasin is a recently discovered HDP active against Gram-positive bacteria with the human pathogen, Staphylococcus aureus (S. aureus) being highly susceptible and the food borne pathogen, Listeria monocytogenes (L. monocytogenes) being less sensitive. In the present study we aimed to use transposon mutagenesis to determine the genetic basis for S. aureus and L. monocytogenes susceptibility to plectasin.

Results

In order to identify genes that provide susceptibility to plectasin we constructed bacterial transposon mutant libraries of S. aureus NCTC8325-4 and L. monocytogenes 4446 and screened for increased resistance to the peptide. No resistant mutants arose when L. monocytogenes was screened on plates containing 5 and 10 fold Minimal Inhibitory Concentration (MIC) of plectasin. However, in S. aureus, four mutants with insertion in the heme response regulator (hssR) were 2-4 fold more resistant to plectasin as compared to the wild type. The hssR mutation also enhanced resistance to the plectasin-like defensin eurocin, but not to other classes of HDPs or to other stressors tested. Addition of plectasin did not influence the expression of hssR or hrtA, a gene regulated by HssR. The genome of L. monocytogenes LO28 encodes a putative HssR homologue, RR23 (in L. monocytogenes EGD-e lmo2583) with 48% identity to the S. aureus HssR, but a mutation in the rr23 gene did not change the susceptibility of L. monocytogenes to plectasin.

Conclusions

S. aureus HssR, but not the homologue RR23 from L. monocytogenes, provides susceptibility to the defensins plectasin and eurocin. Our data suggest that a functional difference between response regulators HssR and RR23 is responsible for the difference in plectasin susceptibility observed between S. aureus and L. monocytogenes.

Synthesis and antimicrobial activity of novel fluorine containing 4-(substituted-2-hydroxybenzoyl)-1H-pyrazoles and pyrazolyl benzo[d]oxazoles

A series of fluorine containing 4-(substituted-2-hydroxybenzoyl) pyrazoles and pyrazolyl benzo[d]oxazoles were synthesized and evaluated for their antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis and antifungal activity against Candida albicans. The antibacterial activities were expressed as the minimum inhibitory concentration (MIC50) in microg/ml. The compounds 1-(3,4-difluorophenyl)-4-(5-fluoro-2-hydroxybenzoyl)-1H-pyrazole (4b), oxime derivatives such as 1-(3,4-difluorophenyl)-1H-pyrazol-4-yl)(2-hydroxy-4-methylphenyl)methanone oxime (5b) and (5-chloro-2-hydroxyphenyl)(1-(3,4-difluorophenyl)-1H-pyrazol-4-yl)methanone oxime (5e) exhibited promising activities against tested bacterial strains. Except compound 1-(3,4-difluorophenyl)-4-(2-hydroxybenzoyl)-1H-pyrazole (4d), none of the other compounds showed promising antifungal activity.