Natural products--the future scaffolds for novel antibiotics?

Antibacterial activity of structurally diverse natural prenylated isobavachalcone derivatives

Isobavachalcone (IBC) is a natural prenylated flavonoid containing chalcone and prenyl chain moieties with a wide range of biological and pharmacological properties. In this work, we synthesized structurally diversified derivatives (IBC-2 to IBC-10) from the natural prenylated chalcone IBC isolated from Psoralea corylifolia and assessed their antibacterial potency against the Gram-positive and Gram-negative bacterial strains S. aureus ATCC 29213, MRSA ATCC 15187, E. coli ATCC25922 and P. aeruginosa ATCC 27853. IBC and IBC-2 exhibited a minimum inhibition concentration (MIC) of 5.0 μM against S. aureus ATCC 29213, whereas IBC-3 exhibited a broad-spectrum activity against Gram-positive and Gram-negative pathogens. Cytotoxicity assessments on the murine RAW 264.7 macrophage cell line revealed minimal to moderate cytotoxicity for IBC-2 and IBC-3 with a favorable selectivity index (>10). Time- and concentration-dependent studies further supported the bactericidal nature of the compounds, as IBC, IBC-2, and IBC-3 exhibited concentration-dependent killing of S. aureus in a time-dependent manner. Furthermore, combination studies, SEM analysis, and PI staining suggest that IBC-3's mechanism of action targets the bacteria's cytoplasmic membrane or cell wall. The bioactive compounds displayed promising drug-like characteristics and a favorable pharmacokinetic profile (ADME-Tox), indicating a projected high oral bioavailability. Structure-activity relationships (SARs) drawn from this study reveal that a prenyl chain at the A-ring and hydroxy functional groups attached to the aromatic rings of chalcone scaffolds are responsible for this antibacterial potential, which will be helpful in the future discovery and development of antibiotics from natural products to overcome the antibiotic resistance crisis.

Lipopeptides development in cosmetics and pharmaceutical applications: A comprehensive review

Lipopeptides are surface active, natural products of bacteria, fungi and green-blue algae origin, having diverse structures and functionalities. In analogy, a number of chemical synthesis techniques generated new designer lipopeptides with desirable features and functions. Lipopetides are self-assembly guided, supramolecular compounds which have the capacity of high-density presentation of the functional epitopes at the surface of the nanostructures. This feature contributes to their successful application in several industry sectors, including food, feed, personal care, and pharmaceutics. In this comprehensive review, the novel class of ribosomally synthesized lipopeptides is introduced alongside the more commonly occuring non-ribosomal lipopeptides. We highlight key representatives of the most researched as well as recently described lipopeptide families, with emphasis on structural features, self-assembly and associated functions. The common biological, chemical and hybrid production routes of lipopeptides, including prominent analogues and derivatives are also discussed. Furthermore, genetic engineering strategies aimed at increasing lipopeptide yields, diversity and biological activity are summarized and exemplified. With respect to application, this work mainly details the potential of lipopeptides in personal care and cosmetics industry as cleansing agents, moisturizer, anti-aging/anti-wrinkling, skin whitening and preservative agents as well as the pharmaceutical industry as anitimicrobial agents, vaccines, immunotherapy, and cancer drugs. Given that this review addresses human applications, we conclude on the topic of safety of lipopeptide formulations and their sustainable production.

Mycobacteriophages in diagnosis and alternative treatment of mycobacterial infections

Antimicrobial resistance is an increasing threat to human populations. The emergence of multidrug-resistant "superbugs" in mycobacterial infections has further complicated the processes of curing patients, thereby resulting in high morbidity and mortality. Early diagnosis and alternative treatment are important for improving the success and cure rates associated with mycobacterial infections and the use of mycobacteriophages is a potentially good option. Since each bacteriophage has its own host range, mycobacteriophages have the capacity to detect specific mycobacterial isolates. The bacteriolysis properties of mycobacteriophages make them more attractive when it comes to treating infectious diseases. In fact, they have been clinically applied in Eastern Europe for several decades. Therefore, mycobacteriophages can also treat mycobacteria infections. This review explores the potential clinical applications of mycobacteriophages, including phage-based diagnosis and phage therapy in mycobacterial infections. Furthermore, this review summarizes the current difficulties in phage therapy, providing insights into new treatment strategies against drug-resistant mycobacteria.

Enhancement of β-Lactam-Mediated Killing of Gram-Negative Bacteria by Lysine Hydrochloride

Widespread bacterial resistance among Gram-negative bacteria is rapidly depleting our antimicrobial arsenal. Adjuvants that enhance the bactericidal activity of existing antibiotics provide a way to alleviate the resistance crisis, as new antimicrobials are becoming increasingly difficult to develop. The present work with Escherichia coli revealed that neutralized lysine (lysine hydrochloride) enhances the bactericidal activity of β-lactams in addition to increasing bacteriostatic activity. When combined, lysine hydrochloride and β-lactam increased expression of genes involved in the tricarboxylic acid (TCA) cycle and raised reactive oxygen species (ROS) levels; as expected, agents known to mitigate bactericidal effects of ROS reduced lethality from the combination treatment. Lysine hydrochloride had no enhancing effect on the lethal action of fluoroquinolones or aminoglycosides. Characterization of a tolerant mutant indicated involvement of the FtsH/HflkC membrane-embedded protease complex in lethality enhancement. The tolerant mutant, which carried a V86F substitution in FtsH, exhibited decreased lipopolysaccharide levels, reduced expression of TCA cycle genes, and reduced levels of ROS. Lethality enhancement by lysine hydrochloride was abolished by treating cultures with Ca2+ or Mg2+, cations known to stabilize the outer membrane. These data, plus damage observed by scanning electron microscopy, indicate that lysine stimulates β-lactam lethality by disrupting the outer membrane. Lethality enhancement of β-lactams by lysine hydrochloride was also observed with Acinetobacter baumannii and Pseudomonas aeruginosa, thereby suggesting that the phenomenon is common among Gram-negative bacteria. Arginine hydrochloride behaved in a similar way. Overall, the combination of lysine or arginine hydrochloride and β-lactam offers a new way to increase β-lactam lethality with Gram-negative pathogens. IMPORTANCE Antibiotic resistance among Gram-negative pathogens is a serious medical problem. The present work describes a new study in which a nontoxic nutrient increases the lethal action of clinically important β-lactams. Elevated lethality is expected to reduce the emergence of resistant mutants. The effects were observed with significant pathogens (Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa), indicating widespread applicability. Examination of tolerant mutants and biochemical measurements revealed involvement of endogenous reactive oxygen species in response to outer membrane perturbation. These lysine hydrochloride-β-lactam data support the hypothesis that lethal stressors can stimulate the accumulation of ROS. Genetic and biochemical work also revealed how an alteration in a membrane protease, FtsH, abolishes lysine stimulation of β-lactam lethality. Overall, the work presents a method for antimicrobial enhancement that should be safe, easy to administer, and likely to apply to other nutrients, such as arginine.

Resistant Bacteria in Broiler Litter Used as Ruminant Feed: Effect of Biotic Treatment

The use of antimicrobial drugs and coccidiostats in poultry farming is widespread, with a significant proportion of these drugs being excreted and released into the environment. The residues of such drugs in poultry litter (PL) can result in the development of antibiotic-resistant bacteria. The impact of different biotic treatments (aerobic, anaerobic, and stacking) on broiler litter (BL) before its use as animal feed has not been studied extensively, nor have the differences between antimicrobial-dependent and independent broiler farms been investigated. This study aimed to determine the resistant bacteria in BL used as ruminant feed before and after litter treatment. The results show that the most resistant bacteria before BL treatment were the Enterococcus species. This study also found that the quantity of amoxicillin-resistant Enterococcus detected in samples from antimicrobial-dependent farms was significantly higher than in those from antimicrobial-independent farms. Additionally, 14% of bacteria were multi-resistant to tetracycline, sulfafurazole, and erythromycin in antimicrobial-independent farm litters, significantly lower than those measured in antimicrobial-dependent broiler farm litter. This study highlights the importance of better understanding, regulating, managing, and using animal waste appropriately to reduce the number of antibiotic-resistant bacteria and minimize the use of antimicrobials that carry high risks for animals, humans, and the environment.

Co-Expression of Transcriptional Regulators and Housekeeping Genes in Streptomyces spp.: A Strategy to Optimize Metabolite Production

The search for novel bioactive compounds to overcome resistance to current therapeutics has become of utmost importance. Streptomyces spp. are one of the main sources of bioactive compounds currently used in medicine. In this work, five different global transcriptional regulators and five housekeeping genes, known to induce the activation or overproduction of secondary metabolites in Streptomyces coelicolor, were cloned in two separated constructs and expressed in 12 different strains of Streptomyces spp. from the in-house CS collection. These recombinant plasmids were also inserted into streptomycin and rifampicin resistant Streptomyces strains (mutations known to enhance secondary metabolism in Streptomyces). Different media with diverse carbon and nitrogen sources were selected to assess the strains' metabolite production. Cultures were then extracted with different organic solvents and analysed to search for changes in their production profiles. An overproduction of metabolites already known to be produced by the biosynthesis wild-type strains was observed such as germicidin by CS113, collismycins by CS149 and CS014, or colibrimycins by CS147. Additionally, the activation of some compounds such as alteramides in CS090a pSETxkBMRRH and CS065a pSETxkDCABA or inhibition of the biosynthesis of chromomycins in CS065a in pSETxkDCABA when grown in SM10 was demonstrated. Therefore, these genetic constructs are a relatively simple tool to manipulate Streptomyces metabolism and explore their wide secondary metabolites production potential.

Design, Synthesis and Biological Evaluation of Novel Pleuromutilin Derivatives Containing 6-Chloro-1-R-1H-pyrazolo[3,4-d]pyrimidine-4-amino Side Chain

Two series of pleuromutilin derivatives were designed and synthesized as inhibitors against Staphylococcus aureus (S. aureus). 6-chloro-4-amino-1-R-1H-pyrazolo[3,4-d]pyrimidine or 4-(6-chloro-1-R-1H-pyrazolo[3,4-d]pyrimidine-4-yl)amino-phenylthiol were connected to pleuromutilin. A diverse array of substituents was introduced at the N-1 position of the pyrazole ring. The in vitro antibacterial activities of these semisynthetic derivatives were evaluated against two standard strains, Methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300, Staphylococcus aureus (S. aureus), ATCC 29213 and two clinical S. aureus strains (144, AD3) using the broth dilution method. Compounds 12c, 19c and 22c (MIC = 0.25 μg/mL) manifested good in vitro antibacterial ability against MRSA which was similar to that of tiamulin (MIC = 0.5 μg/mL). Among them, compound 22c killed MRSA in a time-dependent manner and performed faster bactericidal kinetics than tiamulin in time-kill curves. In addition, compound 22c exhibited longer PAE than tiamulin, and showed no significant inhibition on the cell viability of RAW 264.7, Caco-2 and 16-HBE cells at high doses (≤8 μg/mL). The neutropenic murine thigh infection model study revealed that compound 22c displayed more effective in vivo bactericidal activity than tiamulin in reducing MRSA load. The molecular docking studies indicated that compound 22c was successfully localized inside the binding pocket of 50S ribosomal, and four hydrogen bonds played important roles in the binding of them.

High-Throughput Screening of Natural Product and Synthetic Molecule Libraries for Antibacterial Drug Discovery

Due to the continued emergence of resistance and a lack of new and promising antibiotics, bacterial infection has become a major public threat. High-throughput screening (HTS) allows rapid screening of a large collection of molecules for bioactivity testing and holds promise in antibacterial drug discovery. More than 50% of the antibiotics that are currently available on the market are derived from natural products. However, with the easily discoverable antibiotics being found, finding new antibiotics from natural sources has seen limited success. Finding new natural sources for antibacterial activity testing has also proven to be challenging. In addition to exploring new sources of natural products and synthetic biology, omics technology helped to study the biosynthetic machinery of existing natural sources enabling the construction of unnatural synthesizers of bioactive molecules and the identification of molecular targets of antibacterial agents. On the other hand, newer and smarter strategies have been continuously pursued to screen synthetic molecule libraries for new antibiotics and new druggable targets. Biomimetic conditions are explored to mimic the real infection model to better study the ligand-target interaction to enable the designing of more effective antibacterial drugs. This narrative review describes various traditional and contemporaneous approaches of high-throughput screening of natural products and synthetic molecule libraries for antibacterial drug discovery. It further discusses critical factors for HTS assay design, makes a general recommendation, and discusses possible alternatives to traditional HTS of natural products and synthetic molecule libraries for antibacterial drug discovery.

New Pyrroline Isolated from Antarctic Krill-Derived Actinomycetes Nocardiopsis sp. LX-1 Combining with Molecular Networking

Antarctic krill (Euphausia superba) of the Euphausiidae family comprise one of the largest biomasses in the world and play a key role in the Antarctic marine ecosystem. However, the study of E. superba-derived microbes and their secondary metabolites has been limited. Chemical investigation of the secondary metabolites of the actinomycetes Nocardiopsis sp. LX-1 (in the family of Nocardiopsaceae), isolated from E. superba, combined with molecular networking, led to the identification of 16 compounds a-p (purple nodes in the molecular network) and the isolation of one new pyrroline, nocarpyrroline A (1), along with 11 known compounds 2-12. The structure of the new compound 1 was elucidated by extensive spectroscopic investigation. Compound 2 exhibited broad-spectrum antibacterial activities against A. hydrophila, D. chrysanthemi, C. terrigena, X. citri pv. malvacearum and antifungal activity against C. albicans in a conventional broth dilution assay. The positive control was ciprofloxacin with the MIC values of <0.024 µM, 0.39 µM, 0.39 µM, 0.39 µM, and 0.20 µM, respectively. Compound 1 and compounds 7, 10, and 11 displayed antifungal activities against F. fujikuroi and D. citri, respectively, in modified agar diffusion test. Prochloraz was used as positive control and showed the inhibition zone radius of 17 mm and 15 mm against F. fujikuroi and D. citri, respectively. All the annotated compounds a-p by molecular networking were first discovered from the genus Nocardiopsis. Nocarpyrroline A (1) features an unprecedented 4,5-dihydro-pyrrole-2-carbonitrile substructure, and it is the first pyrroline isolated from the genus Nocardiopsis. This study further demonstrated the guiding significance of molecular networking in the research of microbial secondary metabolites.

Acyldepsipeptide Analogues: A Future Generation Antibiotics for Tuberculosis Treatment

Acyldepsipeptides (ADEPs) are a new class of emerging antimicrobial peptides (AMPs), which are currently explored for treatment of pathogenic infections, including tuberculosis (TB). These cyclic hydrophobic peptides have a unique bacterial target to the conventional anti-TB drugs, and present a therapeutic window to overcome Mycobacterium Tuberculosis (M. tb) drug resistance. ADEPs exerts their antibacterial activity on M. tb strains through activation of the protein homeostatic regulatory protease, the caseinolytic protease (ClpP1P2). ClpP1P2 is normally regulated and activated by the ClpP-ATPases to degrade misfolded and toxic peptides and/or short proteins. ADEPs bind and dysregulate all the homeostatic capabilities of ClpP1P2 while inducing non-selective proteolysis. The uncontrolled proteolysis leads to M. tb cell death within the host. ADEPs analogues that have been tested possess cytotoxicity and poor pharmacokinetic and pharmacodynamic properties. However, these can be improved by drug design techniques. Moreover, the use of nanomaterial in conjunction with ADEPs would yield effective synergistic effect. This new mode of action has potential to combat and eradicate the extensive multi-drug resistance (MDR) problem that is currently faced by the public health pertaining bacterial infections, especially TB.

Pentostatin Biosynthesis Pathway Elucidation and Its Application

Pentostatin (PNT), a nucleoside antibiotic with a 1,3-diazo ring structure, is distributed in several actinomycetes and fungi species. Its special structure makes PNT possess a wide spectrum of biological and pharmacological properties, such as antibacterial, antitrypanosomal, anticancer, antiviral, herbicidal, insecticidal, and immunomodulatory effects. Because of the promising adenosine deaminase inhibitory activity of PNT, its extensive application in the clinical treatment of malignant tumors has been extensively studied. However, the fermentation level of microbial-derived PNT is low and cannot meet medical needs. Because the biosynthesis pathway of PNT is obscure, only high-yield mutant screening and optimization of medium components and fermentation processes have been conducted for enhancing its production. Recently, the biosynthesis pathways of PNT in actinomycetes and fungi hosts have been revealed successively, and the large-scale production of PNT by systematic metabolic engineering will become an inevitable trend. Therefore, this review covers all aspects of PNT research, in which major advances in understanding the resource microorganisms, mechanism of action, and biosynthesis pathway of PNT were achieved and diverse clinical applications of PNT were emphasized, and it will lay the foundation for commercial transformation and industrial technology of PNT based on systematic metabolic engineering.

Antibacterial, Antibiofilm, and Antioxidant Activity of 15 Different Plant-Based Natural Compounds in Comparison with Ciprofloxacin and Gentamicin

Plant-based natural compounds (PBCs) are comparatively explored in this study to identify the most effective and safe antibacterial agent/s against six World Health Organization concern pathogens. Based on a contained systematic review, 11 of the most potent PBCs as antibacterial agents are included in this study. The antibacterial and antibiofilm efficacy of the included PBCs are compared with each other as well as common antibiotics (ciprofloxacin and gentamicin). The whole plants of two different strains of Cannabis sativa are extracted to compare the results with sourced ultrapure components. Out of 15 PBCs, tetrahydrocannabinol, cannabidiol, cinnamaldehyde, and carvacrol show promising antibacterial and antibiofilm efficacy. The most common antibacterial mechanisms are explored, and all of our selected PBCs utilize the same pathway for their antibacterial effects. They mostly target the bacterial cell membrane in the initial step rather than the other mechanisms. Reactive oxygen species production and targeting [Fe-S] centres in the respiratory enzymes are not found to be significant, which could be part of the explanation as to why they are not toxic to eukaryotic cells. Toxicity and antioxidant tests show that they are not only nontoxic but also have antioxidant properties in Caenorhabditis elegans as an animal model.

Isolation and purification of terpenoid compounds from Ferula haussknechtii and evaluation of their antibacterial effects

The roots of F. haussknechtii are used by local people in order to treat wounds and urinary infections. Ferula species are rich in bioactive compounds with biological effects. In line with our previous studies about screening antibacterial natural products, five terpenoid derivatives were purified from Ferula haussknechtii. The separation and purification were performed by column chromatography. Their structures were determined by 1 D and 2 D NMR as hawraman 8-p-hydroxybenzoyl-tovarol (1), ferutinin (2), lancerotriol 6-(p-hydroxybenzoate) (3), chimganin (4), and chimgin (5). Then, the antibacterial effects of the purified compounds were evaluated by measuring their MIC values against Gram-positive and Gram-negative bacteria. The results showed that compound (1) had the most antibacterial effect on Bacillus cereus (MIC = 16 µg/mL). The antibacterial effects of F. haussknechtii compounds are in line with their local application and it is suggested that further studies should be conducted to determine their mechanism of action.

In Vitro Antifungal Antibacterial Activity of Partitions from Euphorbia tirucalli L

We determined the antifungal and antimicrobial sensitivity of Euphorbia tirucalli extracts in vitro. Antifungal and antibacterial activity was determined based on the M38-A and M26-A protocols, respectively. The methanolic and ethanolic partitions demonstrated antidermatophytic activity against Trichophyton rubrum (MIC 125 µg/mL for ethanol and MIC 125 µg/mL for methanol) and T. interdigitalis (MIC 500 µg/mL for ethanol; 125 µg/mL for methanol). These partitions also showed antibacterial activity—the ethanolic partition had an MIC of 1.56 ± 0.02 mg/mL against methicillin-resistant Staphylococcus aureus (clinical isolate), 6.25 ± 0.04 mg/mL against Staphylococcus aureus BAA-44, 3.13 ± 0.13 mg/mL against Pseudomonas aeruginosa 27853, and 3.13 ± 0.15 mg/mL against Escherichia coli ATCC 25922; the methanolic partition showed an MIC of 1.56 ± 0.02 mg/mL against P. aeruginosa 27853 and 1.56 ± 0.043 mg/mL against E. coli ATCC 25922. These partitions show promise as antimicrobial agents or adjuvants in the treatment of infections caused by these microorganisms.

Bioactivity-Guided Screening of Antimicrobial Secondary Metabolites from Antarctic Cultivable Fungus Acrostalagmus luteoalbus CH-6 Combined with Molecular Networking

With the increasingly serious antimicrobial resistance, discovering novel antibiotics has grown impendency. The Antarctic abundant microbial resources, especially fungi, can produce unique bioactive compounds for adapting to the hostile environment. In this study, three Antarctic fungi, Chrysosporium sp. HSXSD-11-1, Cladosporium sp. HSXSD-12 and Acrostalagmus luteoalbus CH-6, were found to have the potential to produce antimicrobial compounds. Furthermore, the crude extracts of CH-6 displayed the strongest antimicrobial activities with 72.3–84.8% growth inhibition against C. albicans and Aeromonas salmonicida. The secondary metabolites of CH-6 were researched by bioactivity tracking combined with molecular networking and led to the isolation of two new α-pyrones, acrostalapyrones A (1) and B (2), along with one known analog (3), and three known indole diketopiperazines (4–6). The absolute configurations of 1 and 2 were identified through modified Mosher’s method. Compounds 4 and 6 showed strong antimicrobial activities. Remarkably, the antibacterial activity of 6 against A. salmonicida displayed two times higher than that of the positive drug Ciprofloxacin. This is the first report to discover α-pyrones from the genus Acrostalagmus, and the significant antimicrobial activities of 4 and 6 against C. albicans and A. salmonicida. This study further demonstrates the great potential of Antarctic fungi in the development of new compounds and antibiotics.

Air Ambulance: Antimicrobial Power of Bacterial Volatiles

We are currently facing an antimicrobial resistance crisis, which means that a lot of bacterial pathogens have developed resistance to common antibiotics. Hence, novel and innovative solutions are urgently needed to combat resistant human pathogens. A new source of antimicrobial compounds could be bacterial volatiles. Volatiles are ubiquitous produced, chemically divers and playing essential roles in intra- and interspecies interactions like communication and antimicrobial defense. In the last years, an increasing number of studies showed bioactivities of bacterial volatiles, including antibacterial, antifungal and anti-oomycete activities, indicating bacterial volatiles as an exciting source for novel antimicrobial compounds. In this review we introduce the chemical diversity of bacterial volatiles, their antimicrobial activities and methods for testing this activity. Concluding, we discuss the possibility of using antimicrobial volatiles to antagonize the antimicrobial resistance crisis.

Discovery and structure-activity relationships of the quinolinequinones: Promising antimicrobial agents and mode of action evaluation

In our pursuit of developing the novel, potent, and selective antimicrobial agents, we managed to obtain the quinolinequinone for their antimicrobial profile with minimal inhibitory concentrations (MICs) determined against a panel of seven bacterial strains (three gram-positive and four gram-negative bacteria) and three fungi. The structure-activity relationship (SAR) for the quinolinequinone class of antimicrobials was determined. Interestingly, QQ1, QQ4, QQ6-9, QQ12, and QQ13 displayed equal antibacterial potential against S. aureus (MIC = 1.22 mg/L), respectively, to the standard positive control Cefuroxime-Na. QQ10 had the best inhibitory activity with the MIC value of 1.22 mg/L (fourfold more potent compared to reference standard Clotrimazole) against Candida albicans. On the other hand, while QQ10 is not too effective against gram-positive bacteria as much as the other analogs, QQ10 was the most effective quinolinequinones against fungi. Selected quinolinequinones were further evaluated for the mode of action, using in vitro antibiofilm activity, bactericidal activity by using time-kill curve assay, antibiofilm activity, and potential antimicrobial activity against each of 32 clinically obtained resistant strains of Gram-positive Bacteria. The results also revealed that the QQ14 had specific antifungal activity against fungi in particular C. albicans. Our results clearly showed that quinolinequinones are much more active in the inhibition of the biofilm attachment process than the inhibition of mature biofilm formation. Thus, as treatment options are narrowing for Methicillin-resistant Staphylococcus spp., Vancomycin-resistant Staphylococcus spp. daily, the quinolinequinones reported herein display promise as the lead candidates for further clinical applications against serious infections.

Berkchaetoazaphilone B has antimicrobial activity and affects energy metabolism

Antimicrobial resistance has become one of the major threats to human health. Therefore, there is a strong need for novel antimicrobials with new mechanisms of action. The kingdom of fungi is an excellent source of antimicrobials for this purpose because it encompasses countless fungal species that harbor unusual metabolic pathways. Previously, we have established a library of secondary metabolites from 10,207 strains of fungi. Here, we screened for antimicrobial activity of the library against seven pathogenic bacterial strains and investigated the identity of the active compounds using ethyl acetate extraction, activity-directed purification using HPLC fractionation and chemical analyses. We initially found 280 antimicrobial strains and subsequently identified 17 structurally distinct compounds from 26 strains upon further analysis. All but one of these compounds, berkchaetoazaphilone B (BAB), were known to have antimicrobial activity. Here, we studied the antimicrobial properties of BAB, and found that BAB affected energy metabolism in both prokaryotic and eukaryotic cells. We conclude that fungi are a rich source of chemically diverse secondary metabolites with antimicrobial activity.

An umpolung-enabled copper-catalysed regioselective hydroamination approach to α-amino acids

A copper-catalysed regio- and stereoselective hydroamination of acrylates with hydrosilanes and hydroxylamines has been developed to afford the corresponding α-amino acids in good yields. The key to regioselectivity control is the use of hydroxylamine as an umpolung, electrophilic amination reagent. Additionally, a judicious choice of conditions involving the CsOPiv base and DTBM-dppbz ligand of remote steric hindrance enables the otherwise challenging C-N bond formation at the α position to the carbonyl. The point chirality at the β-position is successfully controlled by the Xyl-BINAP or DTBM-SEGPHOS chiral ligand with similarly remote steric bulkiness. The combination with the chiral auxiliary, (-)-8-phenylmenthol, also induces stereoselectivity at the α-position to form the optically active unnatural α-amino acids with two adjacent stereocentres.

Geraniol eradicates Candida glabrata biofilm by targeting multiple cellular pathways

Global burden of fungal infections and associated health risk has accelerated at an incredible pace and needs to be attended at the earliest with an unbeatable therapeutic intervention. Candida glabrata is clinically the most relevant and least drug susceptible Candida species. In the pursuit of mining alternative novel drug candidates, the antifungal activity of a monoterpene phytoactive molecule geraniol (GR) against C. glabrata biofilm was evaluated. Biofilm inhibitory and eradication ability of GR evaluated against C. glabrata along with its clinical isolates. Impact of GR on various cellular pathways was evaluated to delineate its antifungal mode of action. GR has inhibited both planktonic and sessile growth of all the studied C. glabrata strains and eradicated the mature biofilm. GR reduced the carbohydrate and eDNA content, as well as hydrolytic enzyme activity in extracellular matrix of C. glabrata. The chemical profiling, microscopic, and spectroscopic studies revealed that GR targets chitin and β-glucan in cell wall. Further, results highlighted the reduction of cell membrane ergosterol content, and blocking of ABC drug efflux pump by GR which was also confirmed by RT-PCR where expression of CDR1 and ERG4 was downregulated in GR exposed C. glabrata cells. The fluorescence microscopy and flow cytometry results emphasized the alteration in mitochondrial activity, increased Ca⁺² uptake, thus changing the membrane permeability ensuing increased cytochrome C release from mitochondria to cytoplasm. Indeed, GR also has arrested cell cycle in G1/S phase and interfered with DNA replication. These observations suggest GR targets multiple cellular pathways and mediated killing of C. glabrata cells via apoptosis. In conclusion, the present study strengthens the candidacy of GR as novel antifungal therapeutic. Key points • GR inhibits growth and eradicates biofilm of C. glabrata and its clinical isolates. • GR inactivates the hydrolytic enzymes in extracellular matrix. • GR mediates C. glabrata apoptosis by interfering with multiple signaling pathways.

Alkaloids in Contemporary Drug Discovery to Meet Global Disease Needs

An overview is presented of the well-established role of alkaloids in drug discovery, the application of more sustainable chemicals, and biological approaches, and the implementation of information systems to address the current challenges faced in meeting global disease needs. The necessity for a new international paradigm for natural product discovery and development for the treatment of multidrug resistant organisms, and rare and neglected tropical diseases in the era of the Fourth Industrial Revolution and the Quintuple Helix is discussed.

Coumarin-1,2,3-triazole Hybrid Molecules: An Emerging Scaffold for Combating Drug Resistance

Undoubtedly, antibiotics have saved billions of lives, but lack of novel antibiotics, development of resistance mechanisms in almost all clinical isolates of bacteria, and recurrent infections caused by persistent bacteria hamper the successful treatment of the infections. Due to the widespread emergence of resistance, even the new families of anti-microbial agents have a short life expectancy. Drugs acting on a single target often lead to drug resistance and are associated with various side effects. For overcoming this problem, either multidrug therapy, or a single drug acting on multiple targets may be used. The latter is called 'hybrid molecules,' which are formed by clubbing two biologically active pharmacophores together, with or without an appropriate linker. In this rapidly evolving era, the development of natural product-based hybrid molecules may be a super-alternative to multidrug therapy, for combating drug resistance caused by various bacterial and fungal strains. Coumarins (benzopyran-2-one) are one of the earliest reported plant secondary metabolites having a clinically proven diverse range of pharmacological properties. On the other hand, 1,2,3-triazole is a common pharmacophore in many drugs responsible for polar interactions, improving the solubility and binding affinity to biomolecular targets. In this review, we discuss recent advances in Coumarin-1,2,3-triazole hybrids as potential anti-bacterial agents, aiming to provide a useful platform for the exploration of new leads with a broader spectrum, more effectiveness and less toxicity with multiple modes of action for the development of cost-effective and safer drugs in the future.

Effect of various synthesis parameters on the stability of size controlled green synthesis of silver nanoparticles

In this study, we have focused on the green method using Litchi Chinensis Leaf Extract (LCLE) for the synthesis of silver nanoparticles (AgNPs). Here, the experimental control parameters (reducing/stabilizing agent quantity, reaction time and temperature, silver ion concentrations) were studied during the size controlled synthesis of silver nanoparticles and their physicochemical properties have been studied. For biological studies, the stability of AgNPs at physiological pH is of vital importance; hence, post-synthesis solution stability of AgNPs was examined at various pH conditions. Stable AgNPs are formed by treating the aqueous solution of AgNO3 with LCLE. Formation of AgNPs was observed visually by the change in the color and further characterized by the surface Plasmon resonance (SPR) peak observed at 436 nm by UV–vis spectroscopy. The synthesized AgNPs were also characterized for their size distribution by Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM), Transmission electron microscope (TEM), crystalline nature by X-Ray Diffraction (XRD) and Fourier Transform infrared (FITR) for the functional groups present. The size of AgNPs was in the range of 40–50 nm, spherical in with face centered cubic (FCC) structure. The biomolecules (epicatechin) present in LCLE were responsible for reduction, capping, and stabilizing agent of AgNPs. Post- synthesis, the stability of AgNPs has been studied by changes in the SPR peaks at various pH (2–11) conditions using UV–vis spectroscopy. This size controlled nanoparticles are very stable at physiological pH and retain their intrinsic SPR property.

Secondary Metabolites of the Genus Amycolatopsis: Structures, Bioactivities and Biosynthesis

Actinomycetes are regarded as important sources for the generation of various bioactive secondary metabolites with rich chemical and bioactive diversities. Amycolatopsis falls under the rare actinomycete genus with the potential to produce antibiotics. In this review, all literatures were searched in the Web of Science, Google Scholar and PubMed up to March 2021. The keywords used in the search strategy were “Amycolatopsis”, “secondary metabolite”, “new or novel compound”, “bioactivity”, “biosynthetic pathway” and “derivatives”. The objective in this review is to summarize the chemical structures and biological activities of secondary metabolites from the genus Amycolatopsis. A total of 159 compounds derived from 8 known and 18 unidentified species are summarized in this paper. These secondary metabolites are mainly categorized into polyphenols, linear polyketides, macrolides, macrolactams, thiazolyl peptides, cyclic peptides, glycopeptides, amide and amino derivatives, glycoside derivatives, enediyne derivatives and sesquiterpenes. Meanwhile, they mainly showed unique antimicrobial, anti-cancer, antioxidant, anti-hyperglycemic, and enzyme inhibition activities. In addition, the biosynthetic pathways of several potent bioactive compounds and derivatives are included and the prospect of the chemical substances obtained from Amycolatopsis is also discussed to provide ideas for their implementation in the field of therapeutics and drug discovery.

Synthesis and biological evaluation of pentacyclic triterpenoid derivatives as potential novel antibacterial agents

A series of ursolic acid (UA), oleanolic acid (OA) and 18β-glycyrrhetinic acid (GA) derivatives were synthesized by introducing a range of substituted aromatic side-chains at the C-2 position after the hydroxyl group at C-3 position was oxidized. Their antibacterial activities were evaluated in vitro against a panel of four Staphylococcus spp. The results revealed that the introduction of aromatic side-chains at the C-2 position of GA led to the discovery of potent triterpenoid derivatives for inhibition of both drug sensitive and resistant S. aureus, while the other two series derivatives of UA and OA showed no significant antibacterial activity even at high concentrations. In particular, GA derivative 33 showed good potency against all four Staphylococcus spp. (MIC = 1.25-5 μmol/L) with acceptable pharmacokinetics properties and low cytotoxicity in vitro. Molecular docking was also performed using S. aureus DNA gyrase to rationalize the observed antibacterial activity. This series of GA derivatives has strong potential for the development of a new type of triterpenoid antibacterial agent.

Possible Potential Effects of Honey and Its Main Components Against Covid-19 Infection

Coronavirus disease 2019 (COVID-19) is a viral pneumonia that is spreading rapidly worldwide. The main feature of this disease is a severe acute respiratory syndrome and caused by coronavirus 2 (SARS-CoV-2). There are several unknowns about the pathogenesis and therapeutically treatment of COVID-19 infection. In addition, available treatment protocols have not been effective in managing COVID-19 infection. It is proposed that natural anti-oxidants such as lemon, green tea, saffron, curcuma longa, etc. with high flavonoids like safranal, crocin, crocetin, catechins, resveratrol, calebin A, curcumin have therapeutic potential against viral infections. In this context, honey and its main components are being investigated as an option for patients with COVID-19. The present study may indicate that honey and its main components inhibit the entry of the virus into the host cell and its replication as well as modulate the inflammatory cascade. This review provides basic information for the possible potential effects of honey and its main components for fighting with SARS-CoV-2.

The interrelationships between antimicrobial resistance, COVID-19, past, and future pandemics

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 was first reported in Wuhan, China in December 2019 and is associated with high levels of morbidity and mortality. Various types of bacterial and fungal infections occur in patients with COVID-19 with some resistant to antimicrobials that are associated with significantly worse outcomes and deaths. Besides, antimicrobial-resistant (AMR) co-infections are responsible for clinically significant mortality in past pandemics. There is evidence to suggest that factors such as the proliferation of adulterated antimicrobials in some developing countries, international travels, issues with healthcare financing, use/misuse by humans, and in agricultural production and climate change are determinants of AMR at various levels of society. These complex interrelated determinants intersect with AMR in current and past pandemics and could amplify the potential of a future antimicrobial resistance pandemic. Therefore, global concerted interventions targeted at all levels of society to reduce the use/misuse of antimicrobials and disrupt these multifaceted, interrelated, and interdependent factors are urgently needed. This paper leverages prior research to describe complex major determinants of antimicrobial resistance and provides fresh insights into possible intervention strategies to tackle antimicrobial resistance including in the current and future pandemics.

Microbial Biosurfactants in Cosmetic and Personal Skincare Pharmaceutical Formulations

Cosmetic and personal care products are globally used and often applied directly on the human skin. According to a recent survey in Europe, the market value of cosmetic and personal care products in Western Europe reached about 84 billion euros in 2018 and are predicted to increase by approximately 6% by the end of 2020. With these significant sums of money spent annually on cosmetic and personal care products, along with chemical surfactants being the main ingredient in a number of their formulations, of which many have been reported to have the potential to cause detrimental effects such as allergic reactions and skin irritations to the human skin; hence, the need for the replacement of chemical surfactants with other compounds that would have less or no negative effects on skin health. Biosurfactants (surfactants of biological origin) have exhibited great potential such as lower toxicity, skin compatibility, protection and surface moisturizing effects which are key components for an effective skincare routine. This review discusses the antimicrobial, skin surface moisturizing and low toxicity properties of glycolipid and lipopeptide biosurfactants which could make them suitable substitutes for chemical surfactants in current cosmetic and personal skincare pharmaceutical formulations. Finally, we discuss some challenges and possible solutions for biosurfactant applications.

Nitric oxide-inducing Genistein elicits apoptosis-like death via an intense SOS response in Escherichia coli

Increasing prevalence of multidrug-resistant untreatable infections has prompted researchers to trial alternative treatments such as a substitute for traditional antibiotics. This study endeavored to elucidate the antibacterial mechanism(s) of this isoflavone, via analysis of relationship between genistein and Escherichia coli. Furthermore, this investigation analyzed whether genistein generates nitric oxide (NO) in E. coli as NO contributes to cell death. RecA, an essential protein for the bacterial SOS response, was detected through western blot, and the activated caspases decreased without RecA. The results showed that the NO induced by genistein affected the bacterial DNA. Under conditions of acute DNA damage, an SOS response called apoptosis-like death occurred, affecting DNA repair. These results suggested that RecA was bacterial caspase-like protein. In addition, NO was toxic to the bacterial cells and induced dysfunction of the plasma membrane. Thus, membrane depolarization and phosphatidylserine exposure were observed similarly to eukaryotic apoptosis. In conclusion, the combined results demonstrated that the antibacterial mode of action(s) of genistein was a NO-induced apoptosis-like death, and the role of RecA suggested that it contributed to the SOS response of NO defense. KEY POINTS: • Genistein generates nitric oxide in E. coli. • Genistein exhibits intense SOS response in E. coli. • Genistein-induced NO causes apoptosis-like death in E. coli.

Microbial Resistance Movements: An Overview of Global Public Health Threats Posed by Antimicrobial Resistance, and How Best to Counter

Antibiotics changed medical practice by significantly decreasing the morbidity and mortality associated with bacterial infection. However, infectious diseases remain the leading cause of death in the world. There is global concern about the rise in antimicrobial resistance (AMR), which affects both developed and developing countries. AMR is a public health challenge with extensive health, economic, and societal implications. This paper sets AMR in context, starting with the history of antibiotics, including the discovery of penicillin and the golden era of antibiotics, before exploring the problems and challenges we now face due to AMR. Among the factors discussed is the low level of development of new antimicrobials and the irrational prescribing of antibiotics in developed and developing countries. A fundamental problem is the knowledge, attitude, and practice (KAP) regarding antibiotics among medical practitioners, and we explore this aspect in some depth, including a discussion on the KAP among medical students. We conclude with suggestions on how to address this public health threat, including recommendations on training medical students about antibiotics, and strategies to overcome the problems of irrational antibiotic prescribing and AMR.

Antimicrobial Importance of Medicinal Plants in Nigeria

Despite the success of antibiotic discovery, infectious diseases remain the second leading source of death worldwide, while the resistance to antibiotics is among the significant problems in the twenty-first century. Medicinal plants are very rich in phytochemicals which can be structurally optimized and processed into new drugs. Nigeria enjoys a diverse collection of medicinal plants, and joint research has ascertained the efficacy of these plants. Plants such as guava (Psidium guajava), ginger (Zingiber officinale), neem (Azadirachta indica), and moringa (Moringa oleifera) have been found to exhibit broad range of antimicrobial activities. Studies on Nigerian plants have shown that they contain alkaloids, polyphenols, terpenes, glycosides, and others with possible therapeutic potentials. The antimicrobial activities of some new compounds such as alloeudesmenol, hanocokinoside, orosunol, and 8-demethylorosunol, identified from medicinal plants in Nigeria, are not yet explored. Further investigation and optimization of these compounds will facilitate the development of new sets of pharmacologically acceptable antimicrobial agents. This review study revealed the efficacy of medicinal plants as an alternative therapy in combating and curtailing the development and survival of multidrug-resistant pathogens coupled with the toxic effects of some antibiotics. Due to enormous therapeutic possibilities buried in medicinal plants, there is a need for more research into unique fingerprints and novel compounds that can provide cure to the neglected tropical diseases (NTDs) of humans and animals facing Africa, especially Nigeria.

Cysteine-rich antimicrobial peptides from plants: The future of antimicrobial therapy

There has been a spurt in the spread of microbial resistance to antibiotics due to indiscriminate use of antimicrobial agents in human medicine, agriculture, and animal husbandry. It has been realized that conventional antibiotic therapy would be less effective in the coming decades and more emphasis should be given for the development of novel antiinfective therapies. Cysteine rich peptides (CRPs) are broad-spectrum antimicrobial agents that modulate the innate immune system of different life forms such as bacteria, protozoans, fungi, plants, insects, and animals. These are also expressed in several plant tissues in response to invasion by pathogens, and play a crucial role in the regulation of plant growth and development. The present work explores the importance of CRPs as potent antimicrobial agents, which can supplement and/or replace the conventional antibiotics. Different plant parts of diverse plant species showed the presence of antimicrobial peptides (AMPs), which had significant structural and functional diversity. The plant-derived AMPs exhibited potent activity toward a range of plant and animal pathogens, protozoans, insects, and even against cancer cells. The cysteine-rich AMPs have opened new avenues for the use of plants as biofactories for the production of antimicrobials and can be considered as promising antimicrobial drugs in biotherapeutics.

Synthesis of novel 18β-glycyrrhetinic piperazine amides displaying significant in vitro and in vivo antibacterial activities against intractable plant bacterial diseases

BACKGROUND

The limited amount of agrochemicals targeting plant bacterial diseases has motivated us to study innovative antibacterial surrogates with fresh modes of action. Notably, fabrication of violent apoptosis inducers to control the reproduction of pathogenic bacteria should be a feasible way to control plant bacterial diseases. To achieve this aim, we constructed a series of novel 18β-glycyrrhetinic piperazine amides based on the natural bioactive ingredient 18β-glycyrrhetinic acid to evaluate the in vitro and in vivo antibacterial activity and induced apoptosis behaviors on tested pathogens.

RESULTS

Screening results suggested that these designed compounds were extremely bioactive against two notorious pathogens, Xanthomonas oryzae pv. oryzae and X. axonopodis pv. citri. This conclusion was highlighted by the biological effects of compounds A₃ and B₁ , affording the related EC₅₀ values of 2.28 and 0.93 μg mL^-1 . In vivo trials confirmed the prospective application for managing rice bacterial blight disease with control efficiency within 50.57-53.70% at 200 μg mL^-1 . In particular, target compounds could induce the generation of excessive reactive oxygen species (ROS) in tested pathogens, subsequently leading to a strong apoptotic effect at a very low drug concentration (≤ 10 μg mL^-1 ). This finding was consistent with the observed ROS-enhanced fluorescent images and morphological changes of pathogens from scanning electron microscopy patterns.

CONCLUSION

Given these features, we anticipate that these novel piperazine-tailored 18β-glycyrrhetinic hybrids can provide an perceptible insight for fighting bacterial infections by activation of the apoptosis mechanism. Novel 18β-glycyrrhetinic piperazine amides were reported to have excellent antibacterial efficacy toward phytopathogens Xanthomonas oryzae pv. oryzae and X. axonopodis pv. citri. A possible apoptosis mechanism was proposed from the remarkable apoptotic behaviors triggered by target compounds. © 2020 Society of Chemical Industry.

Characterization of anti-BCG benz[α]anthraquinones and new siderophores from a Xinjiang desert-isolated rare actinomycete Nocardia sp. XJ31

Abstract

The current global demand for novel anti-TB drugs has drawn urgent attention on the discovery of natural product compounds with anti-TB activity. Lots of efforts have emphasized on environmental samples from unexplored or underexplored natural habits and identified numerous rare actinomycete taxa producing structurally diverse bioactive natural products. Herein, we report a survey of the rare actinobacteria diversity in Xinjiang region together with the discovery of anti-TB active natural products from these strains. We have collected 17 soil samples at different sites with different environmental conditions, from which 39 rare actinobacteria were identified by using a selective isolation strategy with 5 media variations. Among those isolated strains, XJ31 was identified as a new Nocardia sp. based on 16S rRNA gene analysis. Through one strain-many compounds (OSMAC) strategy combined with anti-Bacillus Calmette-Guérin bioassay-guided isolation, two groups of compounds were identified. They were twelve siderophores (nocardimicins, 1-12) and two anthraquinones (brasiliquinones, 13 and 14) and ten of them were identified as new compounds. The structures of the purified compounds were elucidated using HR-ESI-MS, 1D NMR, and 2D NMR techniques. The anti-TB bioassays revealed that the two benz[α]anthraquinones have potent activity against BCG (MICs = 25 μM), which can be used as a promising start point for further anti-TB drug development.

Key points

• Ten new natural products were identified from Nocardia sp. XJ31.

• Brasiliquinones13and14showed moderate anti-BCG activity.

Electronic supplementary material

The online version of this article (10.1007/s00253-020-10842-2) contains supplementary material, which is available to authorized users.

FDA Approved Drug Library Screening Identifies Robenidine as a Repositionable Antifungal

Due to the increasing prevalence of pathogenic fungal infections, the emergence of antifungal resistant clinical isolates worldwide, and the limited arsenal of available antifungals, developing new antifungal strategies is imperative. In this study, we screened a library of 1068 FDA-approved drugs to identify hits that exhibit broad-spectrum antifungal activity. Robenidine, an anticoccidial agent which has been widely used to treat coccidian infections of poultry and rabbits, was identified in this screen. Physiological concentration of robenidine (8 μM) was able to significantly inhibit yeast cell growth, filamentation and biofilm formation of Candida albicans – the most extensively studied human fungal pathogen. Moreover, we observed a broad-spectrum antifungal activity of this compound against fluconazole resistant clinical isolates of C. albicans, as well as a wide range of other clinically relevant fungal pathogens. Intriguingly, robenidine-treated C. albicans cells were hypersensitive to diverse cell wall stressors, and analysis of the cell wall structure by transmission electron microscopy (TEM) showed that the cell wall was severely damaged by robenidine, implying that this compound may target the cell wall integrity signaling pathway. Indeed, upon robenidine treatment, we found a dose dependent increase in the phosphorylation of the cell wall integrity marker Mkc1, which was decreased after prolonged exposure. Finally, we provide evidence by RNA-seq and qPCR that Rlm1, the downstream transcription factor of Mkc1, may represent a potential target of robenidine. Therefore, our data suggest that robenidine, a FDA approved anti-coccidiosis drug, displays a promising and broadly effective antifungal strategy, and represents a potentially repositionable candidate for the treatment of fungal infections.

Silva L, Gonçales RA, Neves BJ, Soares CM, Pereira M. Setting New Routes for Antifungal Drug Discovery Against Pathogenic Fungi

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Fungal diseases are life-threatening to human health and responsible for millions of deaths around the world. Fungal pathogens lead to a high number of morbidity and mortality. Current antifungal treatment comprises drugs, such as azoles, echinocandins, and polyenes and the cure is not guaranteed. In addition, such drugs are related to severe side effects and the treatment lasts for an extended period. Thus, setting new routes for the discovery of effective and safe antifungal drugs should be a priority within the health care system. The discovery of alternative and efficient antifungal drugs showing fewer side effects is time-consuming and remains a challenge. Natural products can be a source of antifungals and used in combinatorial therapy. The most important natural products are antifungal peptides, antifungal lectins, antifungal plants, and fungi secondary metabolites. Several proteins, enzymes, and metabolic pathways could be targets for the discovery of efficient inhibitor compounds and recently, heat shock proteins, calcineurin, salinomycin, the trehalose biosynthetic pathway, and the glyoxylate cycle have been investigated in several fungal species. HSP protein inhibitors and echinocandins have been shown to have a fungicidal effect against azole-resistant fungi strains. Transcriptomic and proteomic approaches have advanced antifungal drug discovery and pointed to new important specific-pathogen targets. Certain enzymes, such as those from the glyoxylate cycle, have been a target of antifungal compounds in several fungi species. Natural and synthetic compounds inhibited the activity of such enzymes and reduced the ability of fungal cells to transit from mycelium to yeast, proving to be promisor antifungal agents. Finally, computational biology has developed effective approaches, setting new routes for early antifungal drug discovery since normal approaches take several years from discovery to clinical use. Thus, the development of new antifungal strategies might reduce the therapeutic time and increase the quality of life of patients.

Antibacterial activity of the structurally novel ocotillol-type lactone and its analogues

A novel series of ocotillol-type lactone derivatives were designed and synthesized in order to study their antibacterial activity and structure-activity relationships. Among which, compounds 4j and 4 m were found to be the most active with minimum inhibitory concentrations (MICs) of 1-4 μg/mL against Gram-positive bacteria and showed low cytotoxicity against MCF-7, HEK-293 and HK-2 cells at their MICs. The antibacterial effect of compound 4 m was characterized further by scanning electron microscopy, cytoplasmic β-galactosidase leakage assay and UV-visible analysis. The results showed that 4 m may exert its antibacterial effect by damaging bacterial cell membranes and disrupting the function of DNA, both of which could lead to rapid cell death.

Essential Oil Phytocomplex Activity, a Review with a Focus on Multivariate Analysis for a Network Pharmacology-Informed Phytogenomic Approach

Thanks to omic disciplines and a systems biology approach, the study of essential oils and phytocomplexes has been lately rolling on a faster track. While metabolomic fingerprinting can provide an effective strategy to characterize essential oil contents, network pharmacology is revealing itself as an adequate, holistic platform to study the collective effects of herbal products and their multi-component and multi-target mediated mechanisms. Multivariate analysis can be applied to analyze the effects of essential oils, possibly overcoming the reductionist limits of bioactivity-guided fractionation and purification of single components. Thanks to the fast evolution of bioinformatics and database availability, disease-target networks relevant to a growing number of phytocomplexes are being developed. With the same potential actionability of pharmacogenomic data, phytogenomics could be performed based on relevant disease-target networks to inform and personalize phytocomplex therapeutic application.

A new abyssomicin polyketide with anti-influenza A virus activity from a marine-derived Verrucosispora sp. MS100137

Marine microorganisms live in dramatically different environments and have attracted much attention for their structurally unique natural products with potential strong biological activity. Based on the one strain-many compounds (OSMAC) strategy and liquid chromatography mass spectrometry (LC-MS) methods, our continuing efforts on the investigation of novel active compounds from marine Verrucosispora sp. MS100137 has led to the identification of a new polycyclic metabolite, abyssomicin Y (1), together with six known abyssomicin and proximicin analogs (2-7). Abyssomicin Y is a type I abyssomicin with an epoxide group at C-8 and C-9. Compounds 1-3 showed potent inhibitory effects against the influenza A virus; their observed inhibition rates were 97.9%, 98.3%, and 95.9%, respectively, at a concentration of 10 μM, and they displayed lower cytotoxicity than 4. The structures were determined by different NMR techniques and HRMS experiments. This investigation revealed that OSMAC could serve as a useful method for enabling the activation of the silent genes in the microorganism and for the formation of previously unreported active secondary metabolites.

PA. Review of Antibiotic Resistance, Ecology, Dissemination, and Mitigation in U.S. Broiler Poultry Systems

Since the onset of land application of poultry litter, transportation of microorganisms, antibiotics, and disinfectants to new locations has occurred. While some studies provide evidence that antimicrobial resistance (AMR), an evolutionary phenomenon, could be influenced by animal production systems, other research suggests AMR originates in the environment from non-anthropogenic sources. In addition, AMR impacts the effective prevention and treatment of poultry illnesses and is increasingly a threat to global public health. Therefore, there is a need to understand the dissemination of AMR genes to the environment, particularly those directly relevant to animal health using the One Health Approach. This review focuses on the potential movement of resistance genes to the soil via land application of poultry litter. Additionally, we highlight impacts of AMR on microbial ecology and explore hypotheses explaining gene movement pathways from U.S. broiler operations to the environment. Current approaches for decreasing antibiotic use in U.S. poultry operations are also described in this review.

Serine protease inhibition and modulatory-antibiotic activity of the proteic extract and fractions from Amburana cearensis

This study investigated the inhibitory activity of serine protease, as well as antibacterial and antibiotic modifying activities of the crude extract and fractions of A. cearensis seeds. Microdilution assay was used to evaluate the antibacterial activity and the antibiotic resistance-modulating effects of samples against multiresistant bacteria Staphylococcus aureus (SA10) and Escherichia coli (EC06). In the inhibition test for serine protease, all the samples showed inhibition of enzymatic activity. Crude extract and fractions of A. cearensis seeds showed a Minimum Inhibitory Concentration ≥1024 μg/mL for all microorganisms tested. However, the samples acted as resistance modifying agent, presenting synergism when associated with gentamicin, norfloxacin and penicillin. The present study provides data indicating a possible use of the seeds extract of A. cearensis in association with antibiotics in the fight against bacterial infections.

Antibacterial Potency of Honey

Despite the developments in controlling infectious disease around the world, they are still the second biggest cause of morbidity and mortality due in part to the increase in drug resistance among large numbers of the bacterial strains. This means that new strategies are needed to prevent and treat infectious disease. As a result, several ancient methods have been re-evaluated and the substances/procedures employed historically to cure diseases are now attracting renewed scientific attention. Honey is one such product that used to be widely used to combat bacteria. This review covers the antibacterial activity of honey, its use in the treatment of infection and diseases, and the features that are relevant to its activity.

Patterns of cross-resistance and collateral sensitivity between clinical antibiotics and natural antimicrobials

Bacteria interact with a multitude of other organisms, many of which produce antimicrobials. Selection for resistance to these antimicrobials has the potential to result in resistance to clinical antibiotics when active compounds target the same bacterial pathways. The possibility of such cross-resistance between natural antimicrobials and antibiotics has to our knowledge received very little attention. The antimicrobial activity of extracts from seaweeds, known to be prolific producers of antimicrobials, is here tested against Staphylococcus aureus isolates with varied clinical antibiotic resistance profiles. An overall effect consistent with cross-resistance is demonstrated, with multidrug-resistant S. aureus strains being on average more resistant to seaweed extracts. This pattern could potentially indicate that evolution of resistance to antimicrobials in the natural environment could lead to resistance against clinical antibiotics. However, patterns of antimicrobial activity of individual seaweed extracts vary considerably and include collateral sensitivity, where increased resistance to a particular antibiotic is associated with decreased resistance to a particular seaweed extract. Our correlation-based methods allow the identification of antimicrobial extracts bearing most promise for downstream active compound identification and pharmacological testing.

Antimicrobial Photodynamic Therapy Protocols on Streptococcus mutans with Different Combinations of Wavelengths and Photosensitizing Dyes

The aim of the study is to test the application of different laser wavelengths, with and without different photosensitizing dyes on different types of cultures. Laser irradiation was realized on Streptococcus mutans in both solid and liquid culture media in continuous mode at three different fluences (10, 20, and 30 J/cm2) with a red diode (650 nm) with toluidine blue dye, a blue-violet diode (405 nm) with curcumin dye, and a green diode (532 nm) with erythrosine dye. Without a photosensitizer, no growth inhibition was obtained with the red diode at any fluence value. Inhibition rates of 40.7% and 40.2% were obtained with the blue diode and green diode. The blue diode laser used with curcumin obtained results in terms of growth inhibition up to 99.26% at a fluence of 30 J/cm2. The red diode laser used with toluidine blue obtained results in terms of growth inhibition up to 100% at fluences of 20 and 30 J/cm2. The KTP (potassium-titanyl-phosphate) laser used with erythrosine was able to determine a complete growth inhibition (100%) at the different fluence values. The combination of a laser and its proper color may dramatically change the results in terms of bactericidal effect. It will be interesting to confirm these data by further in vivo studies.

PMAP-23 triggers cell death by nitric oxide-induced redox imbalance in Escherichia coli

BACKGROUND

Antibiotic resistance is a global problem and there is an urgent need to augment the arsenal against pathogenic bacteria. The emergence of different drug resistant bacteria is threatening human lives to be pushed toward the pre-antibiotic era. Antimicrobial peptides (AMPs) are a host defense component against infectious pathogens in response to innate immunity. PMAP-23, an AMP derived from porcine myeloid, possesses antibacterial activity. It is currently not clear how the antibacterial activity of PMAP-23 is manifested.

METHODS

The disruptive effect of nitric oxide (NO) on the catalase activity, reactive oxygen species (ROS) production, DNA oxidation and apoptosis-like death were evaluated using the NO generation inhibitor.

RESULTS

In this investigation, PMAP-23 generates NO in a dose dependent manner. NO deactivated catalase and this antioxidant could not protect Escherichia coli against ROS, especially hydroxyl radical. This redox imbalance was shown to induce oxidative stress, thus leading to DNA strand break. Consequently, PMAP-23 treated E. coli cells resulted in apoptosis-like death. These physiological changes were inhibited when NO generation was inhibited. In the ΔdinF mutant, the levels of DNA strand break sharply increased and the cells were more sensitive to PMAP-23 than wild type.

CONCLUSION

Our data strongly indicates that PMAP-23 mediates apoptosis-like cell death through affecting intracellular NO homeostasis. Furthermore, our results demonstrate that DinF functioned in protection from oxidative DNA damage.

GENERAL SIGNIFICANCE

The identification of PMAP-23 antibacterial activity and mechanism provides a promising antibacterial agent, supporting the role of NO in cell death regulation.

Leptodactylus latrans Amphibian Skin Secretions as a Novel Source for the Isolation of Antibacterial Peptides

Amphibians´ skin produces a diverse array of antimicrobial peptides that play a crucial role as the first line of defense against microbial invasion. Despite the immense richness of wild amphibians in Argentina, current knowledge about the presence of peptides with antimicrobial properties is limited to a only few species. Here we used LC-MS-MS to identify antimicrobial peptides with masses ranging from 1000 to 4000 Da from samples of skin secretions of Leptodactylus latrans (Anura: Leptodactylidae). Three novel amino acid sequences were selected for chemical synthesis and further studies. The three synthetic peptides, named P1-Ll-1577, P2-Ll-1298, and P3-Ll-2085, inhibited the growth of two ATCC strains, namely Escherichia coli and Staphylococcus aureus. P3-Ll-2085 was the most active peptide. In the presence of trifluoroethanol (TFE) and anionic liposomes, it adopted an amphipathic α-helical structure. P2-Ll-1298 showed slightly lower activity than P3-Ll-2085. Comparison of the MIC values of these two peptides revealed that the addition of seven amino acid residues (GLLDFLK) on the N-terminal of P2-Ll-1298 significantly improved activity against both strains. P1-Ll-1577, which remarkably is an anionic peptide, showed interesting antimicrobial activity against E. coli and S. aureus strain, showing marked membrane selectivity and non-hemolysis. Due to this, P1-L1-1577 emerges as a potential candidate for the development of new antibacterial drugs.