Identification of 5,6-dihydroimidazo[2,1-b]thiazoles as a new class of antimicrobial agents

In an effort to develop novel antimicrobial agents against drug-resistant bacterial infections, 5,6-dihydroimidazo[2,1-b]thiazole compounds were synthesized and tested for their antimicrobial activity. Eight compounds comprised by two sub-scaffolds were identified as hits against methicillin-resistant Staphylococcus aureus (MRSA). These hits were modified at 6-position by replacing (S)-6 to (R)-6 configuration and the (R)-isomers increased their antimicrobial activities by two-fold. The most active compound showed a MIC₉₀ value of 3.7 μg/mL against MRSA in a standard microdilution bacterial growth inhibitory assay. This compound protected wax moth worms against MRSA at a dose of 5× MIC using a worm infectious model. This compound also exhibited inhibition of DNA gyrase activity in a DNA gyrase supercoil assay, suggesting the 5,6-dihydroimidazo[2,1-b]thiazoles may target DNA gyrase for the antimicrobial action.     

In Vitro Synergistic Activities of the Hybrid Antimicrobial Peptide MelitAP-27 in Combination with Conventional Antibiotics Against Planktonic and Biofilm Forming Bacteria

The extensive use of antibiotics for the treatment of human infections during the last few decades has led to a dramatic increase in the emergence of multidrug-resistant bacteria (MDRB) among various bacterial strains. Global research is currently focused on finding novel alternative agents with different mechanisms of action rather than the use of conventional antibiotics to counteract the threat of bacterial and biofilm infections. Antimicrobial peptides represent promising alternative agents for conventional antibiotics as these molecules display a broad spectrum of activity against several microorganisms. Recently, we have designed a novel hybrid antimicrobial peptide named MelitAP-27. This peptide has been found to display potent broad spectrum and selective in vitro antimicrobial activities against a wide range of Gram-positive and Gram-negative bacteria. In the present study, the in vitro antimicrobial and antibiofilm activities of the peptide alone and in combination with five different types of antibiotics were assessed against wild-type and resistant Gram-positive and Gram-negative bacterial strains. Our results showed that most of the combination groups displayed a synergistic mode of action against planktonic and biofilm forming bacteria which resulted in decreasing the effective MIC values for MelitAP-27 to the nanomolar concentrations. These effective concentrations were associated with negligible toxicities on mammalian cells. The results of our study indicate that combinations of MelitAP-27 with conventional antibiotics may be pursued as a potential novel treatment strategy against MDRB and biofilm forming bacteria.     

Three new antimicrobial peptides from the scorpion Pandinus imperator

Three novel cysteine-free venom peptides, which were referred to as Pantinin-1, Pantinin-2 and Pantinin-3, respectively, have been identified from the scorpion Pandinus imperator by cDNA cloning strategy. The precursor of each peptide consists of a signal peptide, a mature peptide with no disulfide bridges, and an acidic propeptide with a typical processing signal. Each of the three peptides is an α-helical, cationic and amphipathic molecule with 13 or 14 amino acid residues. Their amino acid sequences are homologous to those of some 13-mer antimicrobial peptides isolated from scorpions. Antimicrobial assay showed that all the three peptides possess relatively strong activities against Gram-positive bacteria and a fungus, but have very weak antimicrobial activities against Gram-negative bacteria. Toxicity assay showed that the three peptides exhibit very low or mild hemolytic activities against human red blood cells. It is interesting to see that Pantinin-3 is able to potently inhibit the growth of vancomycin-resistant Enterococcus (VRE) S13, a pathogen that can cause a number of human infections; this suggests that Pantinin-3 has great potential to be applied in the treatment of VRE infections. Our findings gain new insights into the structure/function relationships of the small linear cationic antimicrobial peptides from scorpions, and provide new templates for designing of antimicrobial agents targeting antibiotic-resistant pathogenic bacteria.     

Identification and Characterization of an Endo/exonuclease in Pneumocystis carinii that is Inhibited by Dicationic Diarylfurans with Efficacy Against Pneumocystis Pneumonia

ABSTRACT Dicationic diarylfurans and dicationic carbazoles are under development as therapeutic agents against opportunistic infections. While their ability to bind to the minor groove of DNA has been established, the complete mechanism of action has not. We demonstrate here that an effective diarylfuran, 2,5-bis[4-(N-isopropylguanyl)phenyl]furan. inhibits an endo/exonuclease activity present in Pneumocystis carinii, Cryptococcus neoformans, Candida albicans , and Saccharomyces cerevisiae. This activity was purified from the particulate fraction of P. carinii. The enzyme requires Mg⁺⁺ or Mn⁺⁺, and shows preferences for single- over double stranded DNA and for AT-rich over GC-rich domains. A panel of 12 dicationic diarylfurans and eight dicationic carbazoles, previously synthesized, were evaluated for inhibition of the purified nuclease and for efficacy against Pneumocystis pneumonia in rats. Among the diarylfurans, potency of nuclease inhibition, in vivo antimicrobial activity, and DNA binding strength were all strongly correlated (p < 0.001). These findings suggest that one target for antimicrobial action of the diarylfurans may be a nucleolytic or other event requiring unpairing of DNA strands. Dicationic carbazoles which were strong nuclease inhibitors all displayed anti- Pneumocystis activity in vivo, but there were also noninhibitory carbazoles with in vivo efficacy.     

Molecular docking analysis of bioactive compounds from Mollugo cerviana (L.) SER with DHFR for antifungal activity

Fungal infections have been increasing in recent years due to growing number of high-risk patients particularly immuno compromised hosts. Candida is the third- or fourth-most-common isolate in nosocomial bloodstream infections. The increase of fungal resistance to classical drugs, the treatment costs, and the fact that most available antifungal drugs have only fungistatic activity, justify the search for new strategies. Identification of therapeutic compounds from plants has been the centre of attraction ever since they were discovered. It is of interest to document the molecular docking analysis of bioactive compounds present in Mollugo cerviana (L.) SER with the DHFR protein target for antifungal activity. We show the optimal binding features of several compounds from the extract with in vivo and in vitro activities. Results of this showed that all compounds showed good antimicrobial activity and a very good antifungal activity against the target DHFR protein. So, these compounds may act as potential drug molecules after the experimental validation.     

Synthesis of novel oxazolidinone antimicrobial agents

The oxazolidinone class of antimicrobials represents a promising advance in the fight against resistant Gram-positive bacterial infections. Four novel oxazolidinone antimicrobial compounds, each containing a benzodioxin ring system, have been prepared. The general synthesis of each compound begins with the construction of a benzodioxin ring system containing a nitro substituent that ultimately becomes the nitrogen of the oxazolidinone ring. Three of the compounds utilize high yielding 'click chemistry' in their final step. The antimicrobial activities of the new oxazolidinones have been measured and the MIC against Staphylococcus aureus for one of the antimicrobials was determined to be 2-3 microg/mL, which is comparable to the well-known oxazolidinone, linezolid.     

Exometabolome analysis identifies pyruvate dehydrogenase as a target for the antibiotic triphenylbismuthdichloride in multiresistant bacterial pathogens

The desperate need for new therapeutics against notoriously antibiotic-resistant bacteria has led to a quest for novel antibacterial target structures and compounds. Moreover, defining targets and modes of action of new antimicrobial compounds remains a major challenge with standard technologies. Here we characterize the antibacterial properties of triphenylbismuthdichloride (TPBC), which has recently been successfully used against device-associated infections. We demonstrate that TPBC has potent antimicrobial activity against many bacterial pathogens. Using an exometabolome profiling approach, a unique TPBC-mediated change in the metabolites of Staphylococcus aureus was identified, indicating that TPBC blocks bacterial pyruvate catabolism. Enzymatic studies showed that TPBC is a highly efficient, uncompetitive inhibitor of the bacterial pyruvate dehydrogenase complex. Our study demonstrates that metabolomics approaches can offer new avenues for studying the modes of action of antimicrobial compounds, and it indicates that inhibition of the bacterial pyruvate dehydrogenase complex may represent a promising strategy for combating multidrug-resistant bacteria.     

1,2,3-Triazole-derived naphthalimides as a novel type of potential antimicrobial agents: Synthesis,antimicrobial activity,interaction with calf thymus DNA and human serum albumin

A series of 1,2,3-triazole-derived naphthalimides as a novel type of potential antimicrobial agents were synthesized and characterized by IR, NMR and HRMS spectra. All the new compounds were screened for their antimicrobial activity against four Gram-positive bacteria, four Gram-negative bacteria and three fungi. Bioactive assay manifested that 3,4-dichlorobenzyl compound 9e and its corresponding hydrochloride 11e showed better anti-Escherichia coli activity than Norfloxacin and Chloromycin. Preliminary research revealed that compound 9e could effectively intercalate into calf thymus DNA to form compound 9e–DNA complex which might block DNA replication and thus exert antimicrobial activities. Human serum albumin could effectively store and carry compound 9e by electrostatic interaction.     

Silver nanoparticles: the powerful nanoweapon against multidrug-resistant bacteria

In the present scenario, pharmaceutical and biomedical sectors are facing the challenges of continuous increase in the multidrug-resistant (MDR) human pathogenic microbes. Re-emergence of MDR microbes is facilitated by drug and/or antibiotic resistance, which is acquired way of microbes for their survival and multiplication in uncomfortable environments. MDR bacterial infections lead to significant increase in mortality, morbidity and cost of prolonged treatments. Therefore, development, modification or searching the antimicrobial compounds having bactericidal potential against MDR bacteria is a priority area of research. Silver in the form of various compounds and bhasmas have been used in Ayurveda to treat several bacterial infections since time immemorial. As several pathogenic bacteria are developing antibiotic resistance, silver nanoparticles are the new hope to treat them. This review discusses the bactericidal potential of silver nanoparticles against the MDR bacteria. This multiactional nanoweapon can be used for the treatment and prevention of drug-resistant microbes.     

Antimicrobial and Antibiofilm Activity of Mauriporin,a Multifunctional Scorpion Venom Peptide

Many pathogenic free living and biofilm forming bacterial organisms can cause serious infections to humans that could consequently have devastating effects on human health. A significant number of these microbial organisms are resistant to almost all known conventional antibiotics and the ability of some these strains to form sessile communities of biofilms increases the resistance ability of bacteria to antibiotic treatment. Global research is currently focused on finding novel therapies to counteract the threat of bacterial and biofilm infections rather than using conventional antibiotics. Mauriporin, a novel cationic α-helical peptide identified from the venom derived cDNA library of the scorpion Androctonus mauritanicus was reported to display selective cytotoxic and anti-proliferative activity against prostate cancer cell lines. In the present study, we investigated the antimicrobial and antibiofilm activities of Mauriporin. Our results show that Mauriporin displays potent antimicrobial activities against a range of Gram-positive and Gram-negative planktonic bacteria with MIC values in the range 5 µM to 10 µM. Mauriporin was also able to prevent Pseudomonas aeruginosa biofilm formation while showing weak hemolytic activity towards human erythrocytes. Studies on the mechanism of action of Mauriporin revealed that the peptide is probably inducing bacterial cell death through membrane permeabilization determined by the release of β-galactosidase enzyme from peptide treated Escherichia coli cells. Moreover, DNA binding studies found that Mauriporin can cause potent binding to intracellular DNA. All these results indicate that Mauriporin has a considerable potential for therapeutic application as a novel drug candidate for eradicating bacterial infections.     

Synthesis and biological evaluation of a class of quinolone triazoles as potential antimicrobial agents and their interactions with calf thymus DNA

A novel series of quinolone triazoles were synthesized and characterized by IR, NMR, MS and HRMS spectra. All the newly prepared compounds were screened for their antimicrobial activities against seven bacteria and four fungi. Bioactive assay manifested that most of new compounds exhibited good or even stronger antibacterial and antifungal activities against the tested strains including multi-drug resistant MRSA in comparison with reference drugs Norfloxacin, Chloromycin and Fluconazole. The preliminary interactive investigations of compound 6b with calf thymus DNA by fluorescence and UV–vis spectroscopic methods revealed that compound 6b could effectively intercalate DNA to form compound 6b–DNA complex which might block DNA replication and thus exert its antimicrobial activities.     

1,2,3‐Triazole Tagged 3H‐Pyrano[2,3‐d]pyrimidine‐6‐carboxylate Derivatives: Synthesis,in Vitro Cytotoxicity,Molecular Docking and DNA Interaction Studies

A series of novel ethyl 2,7‐dimethyl‐4‐oxo‐3‐[(1‐phenyl‐1H‐1,2,3‐triazol‐4‐yl)methyl]‐4,5‐dihydro‐3H‐pyrano[2,3‐d]pyrimidine‐6‐carboxylate derivatives 7a – 7m were efficiently synthesized employing click chemistry approach and evaluated for in vitro cytotoxic activity against four tumor cell lines: A549 (human lung adenocarcinoma cell line), HepG2 (human hematoma), MCF‐7 (human breast adenocarcinoma), and SKOV3 (human ovarian carcinoma cell line). Among the compounds tested, the compounds 7a , 7b , 7f , 7l , and 7m have shown potential and selective activity against human lung adenocarcinoma cell line (A549) with IC₅₀ ranging from 0.69 to 6.74 μm . Molecular docking studies revealed that the compounds 7a , 7b , 7f , 7l , and 7m are potent inhibitors of human DNA topoisomerase‐II and also showed compliance with stranded parameters of drug likeness. The calculated binding constants, k_b, from UV/VIS absorptional binding studies of 7a and 7l with CT‐DNA were 10.77 × 10⁴, 6.48 × 10⁴, respectively. Viscosity measurements revealed that the binding could be surface binding mainly due to groove binding. DNA cleavage study showed that 7a and 7l have the potential to cleave pBR322 plasmid DNA without any external agents.     

Antimicrobial activity of licochalcone E against Staphylococcus aureus and its impact on the production of staphylococcal alpha-toxin

Licochalcone E was firstly isolated from licorice root in 2005, which belongs to the retrochalcone family. Studies on the biological activities of licochalcone E were in the initial stage. In the study, we demonstrated that licochalcone E has potent antimicrobial property against Staphylococcus aureus. Furthermore, via hemolysis, Western blot, and real-time RT-PCR assays, we have shown that subinhibitory concentrations of licochalcone E dosedependently reduces the production of alpha-toxin in both methicillin-sensitive S. aureus (MSSA) and methicillinresistant S. aureus (MRSA). The data suggest that licochalcone E may deserve further investigation as a potential therapeutic against S. aureus infections, or the structure of licochalcone E may be used as a basis for chemical synthesis of novel anti-S. aureus compounds.     

Food as a source for quorum sensing inhibitors: iberin from horseradish revealed as a quorum sensing inhibitor of Pseudomonas aeruginosa

Foods with health-promoting effects beyond nutritional values have been gaining increasing research focus in recent years, although not much has been published on this subject in relation to bacterial infections. With respect to treatment, a novel antimicrobial strategy, which is expected to transcend problems with selective pressures for antibiotic resistance, is to interrupt bacterial communication, also known as quorum sensing (QS), by means of signal antagonists, the so-called QS inhibitors (QSIs). Furthermore, QSI agents offer a potential solution to the deficiencies associated with use of traditional antibiotics to treat infections caused by bacterial biofilms and multidrug-resistant bacteria. Several QSIs of natural origin have been identified, and in this study, several common food products and plants were extracted and screened for QSI activity in an attempt to isolate and characterize previously unknown QSI compounds active against the common opportunistic pathogen Pseudomonas aeruginosa. Several extracts displayed activity, but horseradish exhibited the highest activity. Chromatographic separation led to the isolation of a potent QSI compound that was identified by liquid chromatography-diode array detector-mass spectrometry (LC-DAD-MS) and nuclear magnetic resonance (NMR) spectroscopy as iberin-an isothiocyanate produced by many members of the Brassicaceae family. Real-time PCR (RT-PCR) and DNA microarray studies showed that iberin specifically blocks expression of QS-regulated genes in P. aeruginosa.     

Phytochemical analysis of <Emphasis Type="Italic">Andrographis paniculata</Emphasis> extract and its antimicrobial activity

The present study describes the phytochemical profile and antimicrobial activity of Andrographis paniculata. For the present investigation, two samples of A. paniculata extracts, obtained by extraction in chloroform and chloroform + HCl, respectively, were compared for their antimicrobial activity and further subjected to GC-MS analysis to find out the nature of the compounds responsible for the antimicrobial activity. The antibacterial activities were assessed by measuring the diameter of the inhibition zones, MIC and MBC values. Compared to the chloroform + HCl extract, the chloroform extract showed better antimicrobial activity against all the nine pathogenic bacterial strains tested. The chloroform extract was observed to be active against the opportunistic and pathogenic gram-negative bacteria, indicating its potential application related to noscomial infections. GC-MS results revealed phenols, aromatic carboxylic acids and esters in the chloroform extract to be the molecules responsible for the antimicrobial activity of A. paniculata. This is the first report on analysis of antimicrobial components from A. paniculata, and our results confer the utility of this plant extract in developing a novel broad spectrum antimicrobial agent.     

Comparative assessment of the therapeutic drug targets of C. botulinum ATCC 3502 and C. difficile str. 630 using in silico subtractive proteomics approach

Growing antimicrobial resistance of the pathogens against multiple drugs posed a serious threat to the human health worldwide. This fueled the need of identifying the novel therapeutic targets that can be used for developing new class of the drugs. Recently, there is a substantial rise in the rate of Clostridium infections as well as in the emergence of virulent and antibiotic resistant strains. Hence, there is an urgent need for the identification of potential therapeutic targets and the development of new drugs for the treatment and prevention of Clostridium infections. In the present study, a combinatorial approach involving systems biology and comparative genomics strategy was tested against Clostridium botulinum ATCC 3502 and Clostridium difficile str. 630 pathogens, to render potential therapeutic target at qualitative and quantitative level. This resulted in the identification of five common (present in both the pathogens, 34 in C. botulinum ATCC 3502 and 42 in C. difficile str. 630) drug targets followed by virtual screening–based identification of potential inhibitors employing molecular docking and molecular dynamics simulations. The identified targets will provide a solid platform for the designing of novel wide-spectrum lead compounds capable of inhibiting their catalytic activities against multidrug-resistant Clostridium in the near future.     

Marine Snails and Slugs: a Great Place To Look for Antiviral Drugs

Molluscs, comprising one of the most successful phyla, lack clear evidence of adaptive immunity and yet thrive in the oceans, which are rich in viruses. There are thought to be nearly 120,000 species of Mollusca, most living in marine habitats. Despite the extraordinary abundance of viruses in oceans, molluscs often have very long life spans (10 to 100 years). Thus, their innate immunity must be highly effective at countering viral infections. Antiviral compounds are a crucial component of molluscan defenses against viruses and have diverse mechanisms of action against a wide variety of viruses, including many that are human pathogens. Antiviral compounds found in abalone, oyster, mussels, and other cultured molluscs are available in large supply, providing good opportunities for future research and development. However, most members of the phylum Mollusca have not been examined for the presence of antiviral compounds. The enormous diversity and adaptations of molluscs imply a potential source of novel antiviral compounds for future drug discovery.     

Antifungal activity of 2α,3β-functionalized steroids stereoselectively increases with the addition of oligosaccharides

Invasive fungal infections pose a significant problem to the immune-compromised. Moreover, increased resistance to common antifungals requires development of novel compounds that can be used to treat invasive fungal infections. Naturally occurring steroidal glycosides have been shown to possess a range of functional antimicrobial properties, but synthetic methodology for their development hinders thorough exploration of this class of molecules and the structural components required for broad spectrum antifungal activity. In this report, we outline a novel approach to the synthesis of glycoside-linked functionalized 2α,3β-cholestane and spirostane molecules and present data from in vitro screenings of the antifungal activities against human fungal pathogens and as well as mammalian cell toxicity of these derivatives.