Multi-drug Resistant Microbial Pathogens Research Articles

Antibacterial Potential of Symmetrical Twin-Drug 3,6-Diaminoxanthones.

Global health faces a significant issue with the rise of infectious diseases caused by bacteria, fungi, viruses, and parasites. The increasing number of multi-drug resistant microbial pathogens severely threatens public health worldwide. Antibiotic-resistant pathogenic bacteria, in particular, present a significant challenge. Therefore, there is an urgent need to identify new potential antimicrobial targets and discover new chemical entities that can potentially reverse bacterial resistance. The main goal of this research work was to create and develop a library of 3,6-disubstituted xanthones based on twin drugs and molecular extension approaches to inhibit the activity of efflux pumps. The process involved synthesizing 3,6-diaminoxanthones through the reaction of 9-oxo-9H-xanthene-3,6-diyl bis(trifluoromethanesulfonate) with various primary and secondary amines. The resulting 3,6-disubstituted xanthone derivatives were then tested for their in vitro antimicrobial properties against a range of pathogenic strains and their efficacy in inhibiting the activity of efflux pumps, biofilm formation, and quorum-sensing. Several compounds have exhibited effective antibacterial properties against the Gram-positive bacterial species tested. Xanthone 16, in particular, has demonstrated exceptional efficacy with a remarkable MIC of 11 µM (4 µg/mL) against reference strains Staphylococcus aureus ATCC 25923 and Enterococcus faecalis ATCC 29212, and 25 µM (9 µg/mL) against methicillin-resistant S. aureus 272123. Furthermore, some derivatives have shown potential as antibiofilm agents in a crystal violet assay. The ethidium bromide accumulation assay pinpointed certain compounds inhibiting bacterial efflux pumps. The cytotoxic effect of the most promising compounds was examined in mouse fibroblast cell line NIH/3T3, and two monoamine substituted xanthone derivatives with a hydroxyl substituent did not exhibit any cytotoxicity. Overall, the nature of the substituent was critical in determining the antimicrobial spectra of aminated xanthones.

Design, synthesis and molecular modeling of isatin-aminobenzoic acid hybrids as antibacterial and antibiofilm agents

Number of factors, including newly emerging infectious diseases and an increase in multi-drug resistant microbial pathogens with particular relevance for Gram-positive bacteria, make the treatment of infectious diseases in hospital-based healthcare a major challenge in the medical community. 4-Aminobenzoic acid (PABA), has demonstrated a variety of biological actions particularly, antimicrobial activity. In our study we coupled this vitamin-like molecule with different isatin derivatives. We investigated the antibacterial activity of the synthesized Schiff's bases. The compounds showed high selective activity against Gram-positive bacteria and showed weak or no activity against both Gram-negative bacteria and fungi. Compound 2a showed highest activity against S. aureus and B. subtilis (MIC 0.09 mmol/L). Additionally, these substances exhibit strong anti-B. Subtilis biofilm formation. We were able to shed insight on the binding mode of these new inhibitors using in silico docking of the compounds in the binding sites of a 3D structure of B. subtilis histidine kinase/Walk. The binding free energy of the compound 2a to the catalytic domain walk, of histidine kinase enzyme of B. subtilis bacteria, was calculated using molecular mechanics/generalized born surface area scoring. The key residues for macromolecule–ligand binding were postulated. The optimized 3D protein–ligand binding modes shed light on the B. subtilis HK/Walk–ligand interactions that afford a means to assess binding affinity to design new HK/Walk inhibitor as antibacterial agents.

Visualizing the membrane disruption action of antimicrobial peptides by cryo-electron tomography

The abuse of antibiotics has led to the emergence of multidrug-resistant microbial pathogens, presenting a pressing challenge in global healthcare. Membrane-disrupting antimicrobial peptides (AMPs) combat so-called superbugs via mechanisms different than conventional antibiotics and have good application prospects in medicine, agriculture, and the food industry. However, the mechanism-of-action of AMPs has not been fully characterized at the cellular level due to a lack of high-resolution imaging technologies that can capture cellular-membrane disruption events in the hydrated state. Previously, we reported PepD2M, a de novo-designed AMP with potent and wide-spectrum bactericidal and fungicidal activity. In this study, we use cryo-electron tomography (cryo-ET) and high-speed atomic force microscopy (HS-AFM) to directly visualize the pepD2M-induced disruption of the outer and inner membranes of the Gram-negative bacterium Escherichia coli, and compared with a well-known pore-forming peptide, melittin. Our high-resolution cryo-ET images reveal how pepD2M disrupts the E. coli membrane using a carpet/detergent-like mechanism. Our studies reveal the direct membrane-disrupting consequence of AMPs on the bacterial membrane by cryo-ET, and this information provides critical insights into the mechanisms of this class of antimicrobial agents.

Graphene Oxide Sheets Decorated with Octahedral Molybdenum Cluster Complexes for Enhanced Photoinactivation of Staphylococcus aureus.

The emergence of multidrug-resistant microbial pathogens poses a significant threat, severely limiting the options for effective antibiotic therapy. This challenge can be overcome through the photoinactivation of pathogenic bacteria using materials generating reactive oxygen species upon exposure to visible light. These species target vital components of living cells, significantly reducing the likelihood of resistance development by the targeted pathogens. In our research, we have developed a nanocomposite material consisting of an aqueous colloidal suspension of graphene oxide sheets adorned with nanoaggregates of octahedral molybdenum cluster complexes. The negative charge of the graphene oxide and the positive charge of the nanoaggregates promoted their electrostatic interaction in aqueous medium and close cohesion between the colloids. Upon illumination with blue light, the colloidal system exerted a potent antibacterial effect against planktonic cultures of Staphylococcus aureus largely surpassing the individual contributions of the components. The underlying mechanism behind this phenomenon lies in the photoinduced electron transfer from the nanoaggregates of the cluster complexes to the graphene oxide sheets, which triggers the generation of reactive oxygen species. Thus, leveraging the unique properties of graphene oxide and light-harvesting octahedral molybdenum cluster complexes can open more effective and resilient antibacterial strategies.

Neighborhood socioeconomic status and the human gut microbiome composition: relating socioeconomic environment to microbial diversity and MDRO colonization

Low socioeconomic status is correlated with a greater vulnerability to both chemical and non-chemical stressors, however, there is limited research on how socioeconomic status relates to the human gut microbiome, and subsequent associations with downstream health outcomes. Here, we aimed to examine associations between neighborhood level economic hardship, an indicator of overall cumulative risk, gut microbiome composition and additional cofactors that might be involved in this association including diet quality and food insecurity. We conducted a cross-sectional analysis of 721 adults living in geographically diverse (urban vs. rural) regions of Wisconsin (United States). 16S rRNA gene amplicons were analyzed from human stool samples using QIIME2 to evaluate both the composition and diversity of the gut microbiotas from 721 participants. Next, we determined correlations with each individual’s neighborhood score for socioeconomic status, or Economic Hardship Index (EHI), using simple and zero-inflated negative binomial regression models. Our model of EHI, with alpha diversity (Inverse-Simpson) as an outcome, found a correlation (β= 1.68, p=0.03) that it is partially mediated by food insecurity (p= 0.02). Moreover, we found differential abundances of known health-associated bacteria including members of the genera Bifidobacterium and Akkermansia, and the family Ruminococaceae between high and low levels of EHI that were robust to correction for multiple comparisons. Finally, we discovered a higher prevalence (p=0.03) and number (p=0.02) of multi-drug resistant bacteria isolated from individuals with low alpha-diversity and high EHI. Our analyses suggest that living in low socioeconomic communities is associated with lower gut microbial diversity and potential increase in colonization by multi-drug resistant microbial pathogens. Mediation of associations by food insecurity is consistent with previous work from our group examining impacts of metal exposures on gut microbiome dysbiosis indicating dietary factors play an important role in mitigating environmental influences on gut microbial diversity.

Effect of Antioxidant on ROS Mediated Antifungal Action of ZnO Quantum Dots in Candida albicans

Nanomaterials are increasingly used as new paradigm for treating infectious diseases, wherein redox perturbation using quantum dots (QDs) show tremendous potential in eliminating various multi-drug resistant microbial pathogens. Herein, spherical, monodispersed ZnO QDs of ~5-6 nm size was synthesized. These ZnO QDs significantly inhibited growth of C. albicans cells. The antifungal action of ZnO QDs against C. albicans involved oxidative stress, mediated via augmentation of endogenous reactive oxygen species (ROS). Further, endogenous ROS production by ZnO QDs and their effect on fungal cell killing was investigated in the presence of antioxidant, ascorbic acid. Results showed that antioxidant failed to offer complete protection against ZnO QDs mediated oxidative stress. It is speculated that intracellular ROS alone is not the only mechanism responsible for ZnO QDs mediated microbial toxicity and other mechanisms probably act either in coordinated or parallel manner to induce cell killing, which merit further investigations for medical adoption of ZnO QDs in biomedicine.

Frequency of Isolation and Antibiotic Resistance Patterns of Bacterial Isolates from Wound Infections, National Cancer Institute, Wad-Medani, Sudan, 2021

Background: Disturbance of skin integrity (wound) provides a suitable environment for the growth and multiplication of bacteria. The emerging occurrence and spread of multidrug-resistant microbial pathogens present a significant challenge in providing effective health care and is, therefore, a worldwide medical issue. Aim: The current study reports on the occurrence of possible pathogens associated with wound infections at National Cancer Institute, Wad Madani, Sudan. Methodology: This was a cross-sectional descriptive, hospital-based study including 100 patients with wounds suspected to be infected. Suspicion was dependent on the inability of wounds to heal properly. A structured questionnaire was given to the subjects to acquire demographic information (age, gender, marital status) and the history of antibiotics administration. Wound swabs were collected and processed according to standard procedure and isolated bacteria were tested for their antimicrobial susceptibilities through the disc diffusion technique according to the CLSI guidelines. Results: Morphological identification revealed that the percentage of gram-positive cocci among the isolates was: S. Aureus (66%), and Streptococci (34%). On the other hand, gram-negative bacilli included the following: E coli (48.1%), Proteus vulgaris (19%), Proteus mirabilis (14%), Klebsiella species (9%), Pseudomonas species (5%) and other bacterial species (4%). Most bacterial isolates exhibited a high rate of resistance to cephalosporin generations (Cefixime (69%), Cefuroxime (49%), Cefotaxime (32%), Ceftriaxone (29%), Cefepime (20%)). The majority of bacterial isolates were sensitive to Meropenem (resistance rate 3%). The antibiogram results of the other antibiotics were as follows: Ciprofloxacin (18%), Gentamicin (16%). Conclusion: S. Aureus was the most prevalent bacteria among the isolates with a percentage of 66%. The highest rate of resistance was observed among cephalosporin generations, mainly Cefixime and Cefuroxime with resistance rate of 69% and 49%, respectively.

Synthesis and antimicrobial potential of spirooxindolopyrrolidine tethered oxindole heterocyclic hybrid against multidrug resistant microbial pathogens

Infectious diseases are a major public health concern worldwide and a leading cause of morbidity and mortality. Spirooxindolopyrrolidine moiety is attractive in this connection, because this structural unit predominates in many biologically relevant natural alkaloids and displayed multifarious biological profiles including antimicrobial activities. In present study, we have synthesized new class of spirooxindolopyrrolidine hybrid heterocycles employing multicomponent cycloaddition methodology. Compound thus synthesized were evaluated for their antimicrobial activity against common microbial pathogens. Of the compounds 4a-d, the compound 4b bearing trifluoromethoxy unit on the oxindole ring exhibited significant antimicrobial activity with an inhibition range from 7.00 ± 0.15 to 20.00 ± 0.08 mm and MIC value from 8.00 to >256.00 μg/mL against selected microbial pathogens. Hence, the compound 4b was a potential candidate to compacting infectious diseases causing microbial pathogens. The overall results of this study indicated that compound 4b has higher potential activities against both multidrug-resistant bacteria and fungal pathogens. Further research studies are needed to fully understand their medicinal properties of new hybrid heterocycles that are being developed in our laboratory for potential therapeutic development to treat various diseases caused by microbial pathogens.

Inhibition of multi-drug resistant microbial pathogens using an eco-friendly root extract of Furcraea foetida mediated silver nanoparticles

ObjectivesAdvancement in the biological process of nanoparticles synthesis is an important area of nanotechnology. The aim of this research is to utilize the root extract of Furcraea foetida as reduction and stabilization agents to biosynthesize. Silver nanoparticles (AgNPs) from AgNO3 via a simple green method. MethodsBy utilizing UV–VIS spectroscopy, FTIR, XRD, Zeta potential, and HR-TEM techniques, the nanoparticles have been characterized. The anti-Candida properties of AgNPs were tested using the well-diffusion method in agar plates against five Candida species. ResultsWith an average diameter of 15 nm, the produced AgNPs are spherical. They were found to be stable and non-aggregated. The synthesized nanoparticles were active against all the tested organisms and showed better efficacy compared to Amphotericin B in most cases. The highest level of inhibition was found against C. albicans at 100 µg concentration. ConclusionThe results prove that F. foetida is a very good bioreductant and can be used for one-pot synthesis of stable AgNPs with good anti-Candida activity.

Novel Polyherbal Nanocolloids to Control Bovine Mastitis.

Mastitis is a widespread disease in dairy cattle occurring throughout the world. The increased use of antibiotics brings about the development of antibiotic-resistant microbes. The application of antibiotics in dairy farming led to increased antibiotic resistance and represents a major obstacle for the treatment of mastitis. Recent advancements in nanotechnology led to the development of nanocolloids to overcome disadvantages posed by conventional antimicrobial agents. Hence, a novel, environmentally friendly, cost-effective, biocompatible, and long-term antibacterial represents a promising solution for medicine and farming. Hence, polyherbal nanocolloids (PHNc) was formulated by using the extracts of Syzygium aromaticum, Cinnamomum verum, Emblica officinalis, Terminalia belerica, Terminalia chebula, and Cymbopogon citratus and physicochemically characterized. From mastitis milk samples, microorganisms were isolated including Acinetobacter junii, Klebsiella pneumoniae, Pseudomonas stutzeri, and Acinetobacter baumannii and screened for antibiotic susceptibility. All the isolated strains were tested with PHNc and compared with antibiotics. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and biofilm assays were performed at different concentrations, and antibacterial effects were quantified. In our results, PHNc showed potent bacteriostatic, bactericidal, and antibiofilm activity against all the strains. Our results indicated that PHNc can reduce the virulence factors responsible for infection by different bacterial strains. This study confirmed that PHNc had the potential to inhibit the growth of pathogenic Gram-negative and Gram-positive strains and could be utilized as an alternative to antibiotics to inhibit multidrug-resistant microbial pathogens in cattle.

Biogenic synthesis, characterization and antimicrobial activity of Ixora brachypoda (DC) leaf extract mediated silver nanoparticles

The present investigation was aimed at the evaluation of synthesis, characterization and antimicrobial activity of Ixora brachypoda DC. leaf extract mediated silver nanoparticles (AgNPs). The AgNPs were characterized by UV–Visible (UV–Vis) spectrophotometer, Fourier transform infrared spectroscopy (FTIR), Atomic force microscopy (AFM), Scanning electron microscopy (SEM) with Energy dispersive X-ray spectrometry (EDS), Transmission electron microscopy (TEM), Zeta potential and X-ray diffractometry (XRD). Finally, the antimicrobial activity of synthesized AgNPs was investigated against pathogenic microorganisms. The absorption peak, obtained at 423 nm in UV–Vis analysis, confirmed the synthesis of AgNPs and the presence of biological functional groups involved in the capping and stabilization were determined by FTIR analysis. The other characterizations revealed the details about the AgNPs as spherical, poly-dispersed and size ranging from 18 to 50 nm with an average diameter of 27.76 nm. The zeta potential was calculated to be −30.4 mV and the typical Bragg’s planes in the metallic silver range indicated the confirmation of AgNPs formation. The in-vitro analysis confirmed the antimicrobial potential of I. brachypoda leaf aqueous extract synthesized AgNPs, which effectively inhibited the growth of pathogens and it can be concluded that the I. brachypoda AgNPs can be used as broad-spectrum antimicrobials against multi-drug resistant microbial pathogens.

Synergistic antibacterial effect of inhaled aztreonam and tobramycin fixed dose combination to combat multidrug-resistant Gram-negative bacteria.

The limited therapeutic option for respiratory infections caused by multi-drug resistant microbial pathogens is a major global health threat. Topical delivery of antibacterial combinations to the lung could dramatically enhance antibacterial activities and provide a means to overcome bacterial resistance development. The aim of the study was to investigate the potential of new inhalable dry powder combinations consisting of a fixed dose of aztreonam (Azt) and tobramycin (Tob) using a spray drying process, against antibiotic resistant Gram-negative respiratory pathogens. The interactions of Azt with Tob on resistant Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii were determined by calculating factional inhibitory concentration indices (FICI). A fixed concentration ratio of Azt and Tob that exhibited a synergistic antimicrobial effect was selected and formulated into inhalable dry powders by co-spray drying with and without L-leucine. The obtained dry powders were characterized with respect to the morphology, particle size distribution, solid state, moisture sorption behaviour, and in vitro dissolution. Storage stability, aerosol performance, and in vitro antibacterial activity were also evaluated. Inhalable dry powders consisting of Azt, Tob and L-leucine could be readily obtained via the spray drying process with a fine particle fraction of above 40% as determined using a next generation impactor. The co-spray drying process resulted in amorphous Azt/Tob dry powders with or without the addition of L-leucine as indicated by X-ray powder diffraction. The dissolution rates of the co-spray dried Azt/Tob dry powders were decreased, and the storage stability was improved with an increase in the proportion of L-leucine in the formulations. The inclusion of L-leucine did not affect the minimum inhibitory concentration and the co-spray dried powders reserved the synergistic antibacterial effects and exhibited enhanced antibacterial activities as compared to the individual antibiotic used alone on multidrug-resistant (Azt and Tob resistant) P. aeruginosa 25756 and A. baumannii K31. This study demonstrates that inhalable Azt/Tob dry powders using L-leucine as a moisture protector as well as a dispersing agent can be readily prepared by the spray drying process. This new inhalable fixed dose combinational dry powders may represent an alternative treatment against multidrug-resistant Gram-negative respiratory pathogens.

Novel Methotrexate-Ciprofloxacin Loaded Alginate-Clay Based Nanocomposite as Anticancer and Antibacterial Co-Drug Delivery System.

Purpose: In last decades, by increasing multi-drug resistant microbial pathogens an urgent demand was felt in the development of novel antimicrobial agents.Methods: Promising nanocomposites composed of clay/alginate/imidazolium-based ionic liquid, have been developed via intercalation of calcium alginate and ionic liquid by ion exchange method. These tailored nanocomposites were used as nanocarriers to simultaneously deliver methotrexate (MTX), and ciprofloxacin (CIP), as anticancer and antibacterial agents, respectively to MCF-7 breast cancer cells. Nanocomposites were fully characterized by scanning electron microscopy studies (SEM), X-ray diffraction (XRD), Fourier transforms infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) methods. The in vitro antimicrobial potential of the mentioned nanocomposites in free and dual-drug loaded form was investigated on Pseudomonas aeruginosa and Escherichia coli bacteria. The antitumor activity of nano-formulations was evaluated by both MTT assay and cell cycle arrest.Results: The dual drug-loaded nanocomposites with exceptionally high loading efficiency (MTX: 99 ±0.4% and CIP: 98 ±1.2%) and mean particle size of 70 nm were obtained with obvious pH-responsive MTX and CIP release (both drugs release rate was increased at pH 5.8 compared to 7.4). The antibacterial activity of CIP-loaded nanocomposites was significantly higher in comparison with free CIP (P <0.001). The antitumor activity results revealed that MTX cytotoxicity on MCF-7 cells was significantly higher in nano-formulations compared to free MTX (P <0.001). Both MTX-loaded nanocomposites caused S-phase arrest in MCF-7 cells compared to non-treated cells (P ˂ 0.001). Conclusion: Newly developed smart nanocomposites are potentially effective pH-sustainable delivery systems for enhanced tumor therapy.

Green synthesis of silver nanoparticles from Neurada procumbens and its antibacterial activity against multi-drug resistant microbial pathogens

The aim of this work was to develop a new biological process for the fabrication of silver nanoparticles (Ag-NPs) using the extract of a xerophytic plant (Neurada procumbens) as a reducing agent. The fabricated Ag-NPs can effectively control multi-drug resistant gram-negative rods (MDR-GNRs), which were isolated from the Buraidah Central Hospital (BCH), Saudi Arabia. The predominant MDR-GNR bacteria included Klebsiella pneumoniae, Acinetobacter baumannii, and Escherichia coli. The Ag-NPs were examined by diverse spectral and analytical techniques, and then their antibacterial effects against MDR bacteria were determined. The UV spectroscopy showed absorption peaks between 400 and 455 nm specific to AgNPs. The SEM and TEM results showed a smallsize of Ag-NPs in a range of about 20–50 nm. The XRD pattern showed three major distinctive peaks of Ag-NPs at 38.1°, 44.3° and 64.4° confirming the presence of Ag-NPs. Three multidrug-resistant bacterial strains were used to determine antimicrobial activity by the well-diffusion method. The present workillusrates that synthesized Ag-NPs from the aqueous leaf extract of Neurada procumbens show considerable antibacterial potential against MDR clinical isolates from different patient samples at BCH.

Extreme environments: microbiology leading to specialized metabolites.

The prevalence of multidrug-resistant microbial pathogens due to the continued misuse and overuse of antibiotics in agriculture and medicine is raising the prospect of a return to the preantibiotic days of medicine at the time of diminishing numbers of drug leads. The good news is that an increased understanding of the nature and extent of microbial diversity in natural habitats coupled with the application of new technologies in microbiology and chemistry is opening up new strategies in the search for new specialized products with therapeutic properties. This review explores the premise that harsh environmental conditions in extreme biomes, notably in deserts, permafrost soils and deep-sea sediments select for micro-organisms, especially actinobacteria, cyanobacteria and fungi, with the potential to synthesize new druggable molecules. There is evidence over the past decade that micro-organisms adapted to life in extreme habitats are a rich source of new specialized metabolites. Extreme habitats by their very nature tend to be fragile hence there is a need to conserve those known to be hot-spots of novel gifted micro-organisms needed to drive drug discovery campaigns and innovative biotechnology. This review also provides an overview of microbial-derived molecules and their biological activities focusing on the period from 2010 until 2018, over this time 186 novel structures were isolated from 129 representatives of microbial taxa recovered from extreme habitats.

Synthesis of chitosan-alginate microspheres with high antimicrobial and antibiofilm activity against multi-drug resistant microbial pathogens

The successful treatment of multi-drug resistant microbial pathogens represents a major challenge for public health management. Here, chitosan-alginate (CS/ALG) microspheres with narrow size distribution were fabricated by ionically cross linking method using Ca2+ ions as agents for polymer solidification. The physicochemical properties of CS/ALG microspheres, such as surface morphology and size, were studied by SEM. The functional group interactions were confirmed by Fourier transform infrared (FTIR) spectroscopy. SEM revealed that the CS/ALG microspheres were spherical in shape with smooth surfaces, size was 50–100 μm. The synthesized CS/ALG microspheres showed antibacterial and antibiofilm activity on bacteria of public health relevance. CS/ALG microspheres exhibited antibacterial activity at the concentration of 5–20 μg, with significant inhibitory zones on multiple antibiotic resistant pathogens, including Gram positive Staphylococcus aureus, Enterococcus faecalis, and Gram negative Pseudomonas aeruginosa and Proteus vulgaris. Furthermore, in situ light microscopy and confocal laser scanning microscopy (CLSM) showed that CS/ALG microspheres inhibited the bacterial biofilm formation in S. aureus, E. faecalis P. aeruginosa and P. vulgaris after a single treatment with 40 μg. Overall, our findings underlined that chemically synthesized CS/ALG biomaterial has high antibacterial and antibiofilm activity against a number of microbial pathogens of interest for human health, thus this synthesis route can be further exploited for drug development in current biomedical science.

Synthesis, characterization and evaluation of 1,3,5-triazine aminobenzoic acid derivatives for their antimicrobial activity

BackgroundReplacement of chloride ions in cyanuric chloride give several variants of 1,3,5-triazine derivatives which were investigated as biologically active small molecules. These compounds exhibit antimalarial, antimicrobial, anti-cancer and anti-viral activities, among other beneficial properties. On the other hand, treatment of bacterial infections remains a challenging therapeutic problem because of the emerging infectious diseases and the increasing number of multidrug-resistant microbial pathogens. As multidrug-resistant bacterial strains proliferate, the necessity for effective therapy has stimulated research into the design and synthesis of novel antimicrobial molecules.Results1,3,5-Triazine 4-aminobenzoic acid derivatives were prepared by conventional method or by using microwave irradiation. Using microwave irradiation gave the desired products in less time, good yield and higher purity. Esterification of the 4-aminobenzoic acid moiety afforded methyl ester analogues. The s-triazine derivatives and their methyl ester analogues were fully characterized by FT-IR, NMR (1H-NMR and 13C-NMR), mass spectra and elemental analysis. All the synthesized compounds were evaluated for their antimicrobial activity. Some tested compounds showed promising activity against Staphylococcus aureus and Escherichia coli.ConclusionsThree series of mono-, di- and trisubstituted s-triazine derivatives and their methyl ester analogues were synthesized and fully characterized. All the synthesized compounds were evaluated for their antimicrobial activity. Compounds (10), (16), (25) and (30) have antimicrobial activity against S. aureus comparable to that of ampicillin, while the activity of compound (13) is about 50% of that of ampicillin. Compounds (13) and (14) have antimicrobial activity against E. coli comparable to that of ampicillin, while the activity of compounds (9–12) and (15) is about 50% of that of ampicillin. Furthermore, minimum inhibitory concentrations values for clinical isolates of compounds (10), (13), (14), (16), (25) and (30) were measured. Compounds (10) and (13) were more active against MRSA and E. coli than ampicillin. Invitro cytotoxicity results revealed that compounds (10) and (13) were nontoxic up to 250 µg/mL (with SI = 10) and 125 µg/mL (with SI = 5), respectively.Graphical abstractThree series of mono-, di- and trisubstituted s-triazine derivatives and their methyl ester analogues were synthesized and evaluated for their antimicrobial activity. Several compounds have antimicrobial activity against S. aureus and E. coli comparable to that of ampicillin.

Pharmacological synergism of bee venom and melittin with antibiotics and plant secondary metabolites against multi-drug resistant microbial pathogens

The goal of this study was to investigate the antimicrobial activity of bee venom and its main component, melittin, alone or in two-drug and three-drug combinations with antibiotics (vancomycin, oxacillin, and amikacin) or antimicrobial plant secondary metabolites (carvacrol, benzyl isothiocyanate, the alkaloids sanguinarine and berberine) against drug-sensitive and antibiotic-resistant microbial pathogens. The secondary metabolites were selected corresponding to the molecular targets to which they are directed, being different from those of melittin and the antibiotics.The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were evaluated by the standard broth microdilution method, while synergistic or additive interactions were assessed by checkerboard dilution and time-kill curve assays. Bee venom and melittin exhibited a broad spectrum of antibacterial activity against 51 strains of both Gram-positive and Gram-negative bacteria with strong anti-MRSA and anti-VRE activity (MIC values between 6 and 800 µg/ml). Moreover, bee venom and melittin showed significant antifungal activity (MIC values between 30 and 100 µg/ml). Carvacrol displayed bactericidal activity, while BITC exhibited bacteriostatic activity against all MRSA and VRE strains tested (reference strains and clinical isolates), both compounds showed a remarkable fungicidal activity with minimum fungicidal concentration (MFC) values between 30 and 200 µg/ml. The DNA intercalating alkaloid sanguinarine showed bactericidal activity against MRSA NCTC 10442 (MBC 20 µg/ml), while berberine exhibited bacteriostatic activity against MRSA NCTC 10442 (MIC 40 µg/ml).Checkerboard dilution tests mostly revealed synergism of two-drug combinations against all the tested microorganisms with FIC indexes between 0.24 and 0.50, except for rapidly growing mycobacteria in which combinations exerted an additive effect (FICI = 0.75–1). In time-kill assays all three-drug combinations exhibited a powerful bactericidal synergistic effect against MRSA NCTC 10442, VRE ATCC 51299, and E. coli ATCC 25922 with a reduction of more than 3log10 in the colony count after 24 h. Our findings suggest that bee venom and melittin synergistically enhanced the bactericidal effect of several antimicrobial agents when applied in combination especially when the drugs affect several and differing molecular targets. These results could lead to the development of novel or complementary antibacterial drugs against MDR pathogens.

Discovering new bioactive molecules from microbial sources.

There is an increased need for new drug leads to treat diseases in humans, animals and plants. A dramatic example is represented by the need for novel and more effective antibiotics to combat multidrug-resistant microbial pathogens. Natural products represent a major source of approved drugs and still play an important role in supplying chemical diversity, despite a decreased interest by large pharmaceutical companies. Novel approaches must be implemented to decrease the chances of rediscovering the tens of thousands of known natural products. In this review, we present an overview of natural product screening, focusing particularly on microbial products. Different approaches can be implemented to increase the probability of finding new bioactive molecules. We thus present the rationale and selected examples of the use of hypersensitive assays; of accessing unexplored microorganisms, including the metagenome; and of genome mining. We then focus our attention on the technology platform that we are currently using, consisting of approximately 70 000 microbial strains, mostly actinomycetes and filamentous fungi, and discuss about high-quality screening in the search for bioactive molecules. Finally, two case studies are discussed, including the spark that arose interest in the compound: in the case of orthoformimycin, the novel mechanism of action predicted a novel structural class; in the case of NAI-112, structural similarity pointed out to a possible in vivo activity. Both predictions were then experimentally confirmed.

Synthesis and Antimicrobial Evaluation of Oxazole-2(3H)-thione and 2-Alkylsulfanyl-1,3-oxazole Derivatives

The preparation of oxazole-2(3H)-thiones (OXTs) by condensation of thiocyanic acid on α-hydroxycarbonyl substrates has been revisited. Extension to more complex scaffolds afforded chiral OXTs, whereas carbohydrate-fused 2-alkylsulfanyl-1,3-oxazolines led to original hemiaminal structures. A survey of the reactivity of OXTs with various electrophiles showed Sor N-chemoselectivity based on HSAB parameters. Antimicrobial evaluation of selected synthesized compounds was carried out, from which the hemiaminal 15 emerged as a promising antifungal agent. INTRODUCTION Treatment of infectious diseases still represents a topical challenge. The emergent infections as well as the increasing number of multi-drug resistant microbial pathogens specially Gram-positive bacteria have been a serious concern both in hospital and community settings. Linezolid (1) (ZyvoxTM) (Figure 1) is a member of the oxazolidinone drugs active against most Gram-positive pathogens, namely Staphylococcus aureus (MRSA) and Staphylococcus epidermis (MRSE). Although it has been approved HETEROCYCLES, Vol. 88, No. 2, 2014 1013