Natural products as inspiration for the development of bacterial antibiofilm agents

Bacterial neuraminidase inhibitory chalcones from flowers of Coreopsis lanceolata, their kinetic characterization and antibiofilm effect

BACKGROUND

Bacteria within biofilms are thousand times more resistant to antibiotics. Neuraminidase is a crucial enzyme for bacterial adhesion and biofilm formation, it hydrolyzes glycosidic residue of glycoproteins, glycolipids, and oligosaccharides. Coreopsis lanceolata L. flowers may have a significant potential of bacterial neuraminidase (BNA) inhibition because of high natural abundance of chalcones.

PURPOSE

The investigation of bacterial biofilm inhibitors has emerged as a novel therapeutic strategy against antibiotic resistance. Therefore, individual chalcones were isolated from C. lanceolata and their capacity to inhibit BNA and formation of Escherichia coli biofilm were evaluated.

METHODS

Different chromatographic techniques were used to isolate the compounds (1-12). Enzyme inhibition and detailed kinetic behavior of compounds was determined by estimation of kinetic parameters (Michaelis-Menten constants (Km), maximum velocity (Vmax), dissociation constant for binding with the free enzyme (KI) and enzyme-substate complex (KIS)). Binding affinities (KSV) and binding modes of inhibitors were elucidated by fluorescence quenching and molecular docking, respectively. The natural abundance of chalcones was established through UPLC-Q-TOF/MS. The most potent inhibitor (1) was tested for its ability to inhibit the formation of E. coli biofilm, which was examined by crystal violet assay, scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM).

RESULTS

A series of eight chalcones (1-8) and four chalcone glucosides (9-12), inhibited BNA in a dose-dependent manner with IC50 of 8.3 ∼ 77.0 µM. The most potent chalcones were butein (1, IC50 = 8.3 µM) and its glucoside 9 (IC50 = 13.8 µM). The aglycones (1-8) showed non-competitive inhibition, while chalcone glucosides (9-12) displayed a mixed type I (KI < KIS). Inhibitory behaviors were doubly confirmed by KSV and matched with tendency of IC50. The functional group responsible for BNA inhibition were disclosed as 4'-hydroxyl group on B-ring by structure activity relationship (SAR) and molecular docking experiments. Butein (1) suppressed E. coli biofilm formation by > 50 % at 100 µM according to crystal violet assay, which was confirmed by SEM and CLSM imaging.

CONCLUSION

The results showed that chalcones (1-8) and chalcone glucosides (9-12), metabolites isolated from the flowers of C. lanceolata, had BNA inhibitory and antibiofilm formation effect on E. coli.

Photochemical dearomative skeletal modifications of heteroaromatics

Dearomatization has emerged as a powerful tool for rapid construction of 3D molecular architectures from simple, abundant, and planar (hetero)arenes. The field has evolved beyond simple dearomatization driven by new synthetic technology development. With the renaissance of photocatalysis and expansion of the activation mode, the last few years have witnessed impressive developments in innovative photochemical dearomatization methodologies, enabling skeletal modifications of dearomatized structures. They offer truly efficient and useful tools for facile construction of highly complex structures, which are viable for natural product synthesis and drug discovery. In this review, we aim to provide a mechanistically insightful overview on these innovations based on the degree of skeletal alteration, categorized into dearomative functionalization and skeletal editing, and to highlight their synthetic utilities.

Discovery of Biofilm Inhibitors from the Microbiota of Marine Egg Masses

Biofilms commonly develop in immunocompromised patients, which leads to persistent infections that are difficult to treat. In the biofilm state, bacteria are protected against both antibiotics and the host's immune system; currently, there are no therapeutics that target biofilms. In this study, we screened a chemical fraction library representing the natural product capacity of the microbiota of marine egg masses, namely, the moon snail egg collars. This led to the identification of active fractions targeting both Pseudomonas aeruginosa and Staphylococcus aureus biofilms. Subsequent analysis revealed that a subset of these fractions were capable of eradicating preformed biofilms, all against S. aureus. Bioassay-guided isolation led us to identify pseudochelin A, a known siderophore, as a S. aureus biofilm inhibitor with an IC50 of 88.5 μM. Mass spectrometry-based metabolomic analyses revealed widespread production of pseudochelin A among fractions possessing S. aureus antibiofilm properties. In addition, a key biosynthetic gene involved in producing pseudochelin A was detected on 30% of the moon snail egg collars and pseudochelin A is capable of inhibiting the formation of biofilms (IC50 50.6 μM) produced by ecologically relevant bacterial strains. We propose that pseudochelin A may have a role in shaping the microbiome or protecting the egg collars from microbiofouling.

Plant-derived bioactive compounds for the inhibition of biofilm formation: a comprehensive review

Biofilm formation is a widespread phenomenon that impacts different fields, including the food industry, agriculture, health care and the environment. Accordingly, there is a serious need for new methods of managing the problem of biofilm formation. Natural products have historically been a rich source of varied compounds with a wide variety of biological functions, including antibiofilm agents. In this review, we critically highlight and discuss the recent progress in understanding the antibiofilm effects of several bioactive compounds isolated from different plants, and in elucidating the underlying mechanisms of action and the factors influencing their adhesion. The literature shows that bioactive compounds have promising antibiofilm potential against both Gram-negative and Gram-positive bacterial and fungal strains, via several mechanisms of action, such as suppressing the formation of the polymer matrix, limiting O2 consumption, inhibiting microbial DNA replication, decreasing hydrophobicity of cell surfaces and blocking the quorum sensing network. This antibiofilm activity is influenced by several environmental factors, such as nutritional cues, pH values, O2 availability and temperature. This review demonstrates that several bioactive compounds could mitigate the problem of biofilm production. However, toxicological assessment and pharmacokinetic investigations of these molecules are strongly required to validate their safety.

Nanocomposites against Pseudomonas aeruginosa biofilms: Recent advances, challenges, and future prospects

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that causes life-threatening and persistent infections in immunocompromised patients. It is the culprit behind a variety of hospital-acquired infections owing to its multiple tolerance mechanisms against antibiotics and disinfectants. Biofilms are sessile microbial aggregates that are formed as a result of the cooperation and competition between microbial cells encased in a self-produced matrix comprised of extracellular polymeric constituents that trigger surface adhesion and microbial aggregation. Bacteria in biofilms exhibit unique features that are quite different from planktonic bacteria, such as high resistance to antibacterial agents and host immunity. Biofilms of P. aeruginosa are difficult to eradicate due to intrinsic, acquired, and adaptive resistance mechanisms. Consequently, innovative approaches to combat biofilms are the focus of the current research. Nanocomposites, composed of two or more different types of nanoparticles, have diverse therapeutic applications owing to their unique physicochemical properties. They are emerging multifunctional nanoformulations that combine the desired features of the different elements to obtain the highest functionality. This review assesses the recent advances of nanocomposites, including metal-, metal oxide-, polymer-, carbon-, hydrogel/cryogel-, and metal organic framework-based nanocomposites for the eradication of P. aeruginosa biofilms. The characteristics and virulence mechanisms of P. aeruginosa biofilms, as well as their devastating impact and economic burden are discussed. Future research addressing the potential use of nanocomposites as innovative anti-biofilm agents is emphasized. Utilization of nanocomposites safely and effectively should be further strengthened to confirm the safety aspects of their application.

Marine-derived bioactive materials as antibiofilm and antivirulence agents

Microbial infections are major human health issues, and, recently, the mortality rate owing to bacterial and fungal infections has been increasing. In addition to intrinsic and extrinsic antimicrobial resistance mechanisms, biofilm formation is a key adaptive resistance mechanism. Several bioactive compounds from marine organisms have been identified for use in biofilm therapy owing to their structural complexity, biocompatibility, and economic viability. In this review, we discuss recent trends in the application of marine natural compounds, marine-bioinspired nanomaterials, and marine polymer conjugates as possible therapeutic agents for controlling biofilms and virulence factors. We also comprehensively discuss the mechanisms underlying biofilm formation and inhibition of virulence factors by marine-derived materials and propose possible applications of novel and effective antibiofilm and antivirulence agents.

Total Synthesis and Microbiological Evaluation of Leopolic Acid A and Analogues

New antimicrobial scaffolds are scarce, and there is a great need for the development of novel therapeutics. In this study, we report a convergent 9-step synthesis of leopolic acid A and a series of targeted analogues. The designed compounds allowed for incorporation of non-natural ureido dipeptide moieties and 4- and 5-position substituents around the 2,3-pyrrolidinedione of leopolic acid A. Leopolic acid A displayed modest antimicrobial activity (32 μg/mL) against MRSA, while the most active analogues displayed slightly improved activity (8-16 μg/mL). Additionally, several of the leopolic acid A analogues displayed promising antibiofilm activity, most notably having an MBEC:MIC ratio of ∼1. Overall, this work represents an initial SAR of the natural product and a framework for further optimization of these bioactive scaffolds within the context of bioactive pyrrolidinediones.

Anti-biofilm activity of marine algae-derived bioactive compounds

A large number of microbial species tend to communicate and produce biofilm which causes numerous microbial infections, antibiotic resistance, and economic problems across different industries. Therefore, advanced anti-biofilms are required with novel attributes and targets, such as quorum sensing communication system. Meanwhile, quorum sensing inhibitors as promising anti-biofilm molecules result in the inhibition of particular phenotype expression blocking of cell-to-cell communication, which would be more acceptable than conventional strategies. Many natural products are identified as anti-biofilm agents from different plants, microorganisms, and marine extracts. Marine algae are promising sources of broadly novel compounds with anti-biofilm activity. Algae extracts and their metabolites such as sulfated polysaccharides (fucoidan), carotenoids (zeaxanthin and lutein), lipid and fatty acids (γ-linolenic acid and linoleic acid), and phlorotannins can inhibit the cell attachment, reduce the cell growth, interfere in quorum sensing pathway by blocking related enzymes, and disrupt extracellular polymeric substances. In this review, the mechanisms of biofilm formation, quorum sensing pathway, and recently identified marine algae natural products as anti-biofilm agents will be discussed.

Endophytes: a uniquely tailored source of potential antibiotic adjuvants

Multidrug microbial resistance is risking an annual loss of more than 10 million people' lives by 2050. Solutions include the rational use of antibiotics and the use of drugs that reduce resistance or completely obliterate them. Here endophytes come to play due to their high-yield production and inherent nature to produce antimicrobial molecules. Around 40%, 45% and 17% of antibacterial agents were obtained from fungi, actinomycetes, and bacteria, respectively, whose secondary metabolites revealed effectiveness against resistant microbes such as MRSA, MRSE, and Shigella flexneri. Endophyte's role was not confined to bactericidal effect but extended to other mechanisms against MDR microbes, among which was the adjuvant role or the "magic bullets". Scarce focus was given to antibiotic adjuvants, and many laboratories today just screen for the antimicrobial activity without considering combinations with traditional antibiotics, which means real loss of promising resistance combating molecules. While some examples of synthetic adjuvants were introduced in the last decade, the number is still far from covering the disused antibiotics and restoring them back to clinical use. The data compiled in this article demonstrated the significance of quorum sensing as a foreseen mechanism for adjuvants from endophytes secondary metabolites, which call for urgent in-depth studies of their molecular mechanisms. This review, comprehensively and for the first time, sheds light on the significance of endophytes secondary metabolites in solving AMR problem as AB adjuvants.

Disruption of Communication: Recent Advances in Antibiofilm Materials with Anti-Quorum Sensing Properties

Biofilm contamination presents a significant threat to public health, the food industry, and aquatic/marine-related applications. In recent decades, although various methods have emerged to combat biofilm contamination, the intricate and persistent nature of biofilms makes complete eradication challenging. Therefore, innovative alternative solutions are imperative for addressing biofilm formation. Instead of solely focusing on the eradication of mature biofilms, strategically advantageous measures involve the delay or prevention of biofilm formation on surfaces. Quorum sensing, a communication system enabling bacteria to coordinate their behavior based on population density, plays a pivotal role in biofilm formation for numerous microbial species. Materials possessing antibiofilm properties that target quorum sensing have gained considerable attention for their potential to prevent biofilm formation. This Review consolidates recent research progress on the utilization of materials with antiquorum sensing properties for combating biofilm formation. These materials can be categorized into three distinct types: (i) antibiofilm nanomaterials, (ii) antibiofilm surfaces, and (iii) antibiofilm hydrogels with antiquorum sensing capabilities. Finally, the Review concludes with a brief discussion of current challenges and outlines potential avenues for future research.

A systematic review of astragaloside IV effects on animal models of diabetes mellitus and its complications

Context

Diabetes mellitus (DM) is one of the fastest-growing diseases worldwide; however, its pathogenesis remains unclear. Complications seriously affect the quality of life of patients in the later stages of diabetes, ultimately leading to suffering. Natural small molecules are an important source of antidiabetic agents.

Objective

Astragaloside IV (AS-IV) is an active ingredient of Astragalus mongholicus (Fisch.) Bunge. We reviewed the efficacy and mechanism of action of AS-IV in animal and cellular models of diabetes and the mechanism of action of AS-IV on diabetic complications in animal and cellular models. We also summarized the safety of AS-IV and provided ideas and rationales for its future clinical application.

Methods

Articles on the intervention in DM and its complications using AS-IV, such as those published in SCIENCE, PubMed, Springer, ACS, SCOPUS, and CNKI from the establishment of the database to February 2022, were reviewed. The following points were systematically summarized: dose/concentration, route of administration, potential mechanisms, and efficacy of AS-IV in animal models of DM and its complications.

Results

AS-IV has shown therapeutic effects in animal models of DM, such as alleviating gestational diabetes, delaying diabetic nephropathy, preventing myocardial cell apoptosis, and inhibiting vascular endothelial dysfunction; however, the potential effects of AS-IV on DM should be investigated.

Conclusion

AS-IV is a potential drug for the treatment of diabetes and its complications, including diabetic vascular disease, cardiomyopathy, retinopathy, peripheral neuropathy, and nephropathy. In addition, preclinical toxicity studies indicate that it appears to be safe, but the safe human dose limit is yet to be determined, and formal assessments of adverse drug reactions among humans need to be further investigated. However, additional formulations or structural modifications are required to improve the pharmacokinetic parameters and facilitate the clinical use of AS-IV.

Microbial anti-biofilms: types and mechanism of action

Biofilms have been recognized as a serious threat to public health as it protects microbes from antimicrobials, immune defence mechanisms, chemical treatments and nutritional stress. Biofilms are also a source of concern in industries and water treatment because their presence compromises the integrity of equipment. To overcome these problems, it is necessary to identify novel anti-biofilm compounds. Products of microorganisms have been identified as promising broad-spectrum anti-biofilm agents. These natural products include biosurfactants, antimicrobial peptides, enzymes and bioactive compounds. Anti-biofilm products of microbial origin are chemically diverse and possess a broad spectrum of activities against biofilms. The objective of this review is to give an overview of the different types of microbial anti-biofilm products and their mechanisms of action.

Synthesis, biological activities and mechanism studies of 1,3,4-oxadiazole analogues of petiolide A as anticancer agents

In order to develop new natural product-based anticancer agents, a series of 1,3,4-oxadiazole analogues based on petiolide A were prepared and evaluated for their anticancer activities by MTT method. The structures of all analogues were characterized by various spectral analyses, and B9 was further confirmed by X-ray crystallography. Among all the synthesized compounds, B1 displayed the most promising growth inhibitory effect on colon cancer cells (HCT116) with the IC50 value of 8.53 μM. Flow cytometric analysis exhibited that B1 arrested the cell cycle at G2 phase and induced apoptosis. Additionally, network pharmacology analysis calculated that B1 might target several key proteins, including AKT serine/threonine kinase 1 (AKT1), SRC proto-oncogene, non-receptor tyrosine kinase (SRC) and epidermal growth factor receptor (EGFR). Furthermore, molecular docking study indicated that B1 had potentially high binding affinity to these three target proteins. Given these results, analogue B1 could be deeply developed as potential anticancer agents.

An Overview of Biofilm-Associated Infections and the Role of Phytochemicals and Nanomaterials in Their Control and Prevention

Biofilm formation is considered one of the primary virulence mechanisms in Gram-positive and Gram-negative pathogenic species, particularly those responsible for chronic infections and promoting bacterial survival within the host. In recent years, there has been a growing interest in discovering new compounds capable of inhibiting biofilm formation. This is considered a promising antivirulence strategy that could potentially overcome antibiotic resistance issues. Effective antibiofilm agents should possess distinctive properties. They should be structurally unique, enable easy entry into cells, influence quorum sensing signaling, and synergize with other antibacterial agents. Many of these properties are found in both natural systems that are isolated from plants and in synthetic systems like nanoparticles and nanocomposites. In this review, we discuss the clinical nature of biofilm-associated infections and some of the mechanisms associated with their antibiotic tolerance. We focus on the advantages and efficacy of various natural and synthetic compounds as a new therapeutic approach to control bacterial biofilms and address multidrug resistance in bacteria.

Unexpected Noremestrin with a Sulfur-Bearing 15-Membered Macrocyclic Lactone from Emericella sp. 1454

Two previous unreported epipolythiodioxopiperazines of the emestrin family, namely, noremestrin A (1) and secoemestrin E (2), were successfully isolated from the fungal source Emericella sp. 1454. Employing comprehensive spectroscopic techniques, such as high-resolution electrospray ionization mass spectrometry, infrared, and nuclear magnetic resonance (NMR), along with NMR and electronic circular dichroism calculations, the chemical structures of compounds 1 and 2 were elucidated. Particularly noteworthy is the distinctive nature of noremestrin A, representing the inaugural instance of a noremestrin variant incorporating a sulfur-bearing 15-membered macrocyclic lactone moiety. Compounds 1 and 2 exhibited weak cytotoxic activities against the human chronic myelocytic leukemia cell lines MEG-01 and K562.

Curcusinol from the fruit of Carex baccans with antibacterial activity against multidrug-resistant strains

ETHNOPHARMACOLOGICAL RELEVANCE

Carex baccans, known as Shan-Bai-Zi or Ye-Gao-Liang in China, is a traditional medicinal herb used by several ethnic groups in Yunnan Province. It is utilized for the treatment of wound infections, ulcers, and dysentery. However, there is currently a dearth of research reports on its antimicrobial potential.

AIM OF THE STUDY

The substance basis of the antimicrobial activity of C. baccans will be unveiled, and the in vitro and in vivo antibacterial activities against multidrug-resistant bacteria of its major active compounds, as well as their preliminary mechanisms of action, will be investigated.

MATERIALS AND METHODS

An antibacterial bioactivity-guided isolation method was used to isolate and identify the active compound curcusinol from C. baccans. UPLC-DAD-MS was employed for the quantitative analysis of curcusinol. The antibacterial activity, resistance profile, synergistic effects, anti-biofilm activity, and potential mechanisms of action of curcusinol against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and other multidrug-resistant bacteria (Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii) were investigated using various methods, including the broth microdilution method, scanning electron microscopy, time kill assay, multi-generational resistance induction assay, checkerboard synergy assay, anti-biofilm assay, and metabolomics. Furthermore, the therapeutic efficacy of curcusinol was assessed in vivo by establishing an animal skin wound infection model of MRSA.

RESULTS

Curcusinol was isolated from the fruit of C. baccans, which accounts for 3.1% of the dry weight of the fruit. Curcusinol exhibited significant bactericidal and anti-biofilm activities against antibiotic-resistant Gram-positive bacteria in vitro. Furthermore, curcusinol acted as an antibiotic adjuvant to enhance the activity of various commonly used antibiotics against both Gram-positive and Gram-negative antibiotic-resistant bacteria without cytotoxicity to mammalian cells (A549 and RAW264.7) at 64 μM. Moreover, curcusinol affected arginine biosynthesis, cysteine and methionine metabolism, and alanine, aspartate, and glutamate metabolism significantly in MRSA cells under stress. Additionally, curcusinol effectively treated MRSA-infected mouse skin wounds and accelerated wound healing in vivo.

CONCLUSIONS

The results of this study not only support the traditional uses of C. baccans but also demonstrate that its major active compound, curcusinol, is an effective plant-derived bactericidal agent and antibacterial adjuvant with potential applications in the treatment of skin infections.

Antibiofilm activity of marine microbial natural products: potential peptide- and polyketide-derived molecules from marine microbes toward targeting biofilm-forming pathogens

Controlling and treating biofilm-related infections is challenging because of the widespread presence of multidrug-resistant microbes. Biofilm, a naturally occurring matrix of microbial aggregates, has developed intricate and diverse resistance mechanisms against many currently used antibiotics. This poses a significant problem, especially for human health, including clinically chronic infectious diseases. Thus, there is an urgent need to search for and develop new and more effective antibiotics. As the marine environment is recognized as a promising reservoir of new biologically active molecules with potential pharmacological properties, marine natural products, particularly those of microbial origin, have emerged as a promising source of antibiofilm agents. Marine microbes represent an untapped source of secondary metabolites with antimicrobial activity. Furthermore, marine natural products, owing to their self-defense mechanisms and adaptation to harsh conditions, encompass a wide range of chemical compounds, including peptides and polyketides, which are primarily found in microbes. These molecules can be exploited to provide novel and unique structures for developing alternative antibiotics as effective antibiofilm agents. This review focuses on the possible antibiofilm mechanism of these marine microbial molecules against biofilm-forming pathogens. It provides an overview of biofilm development, its recalcitrant mode of action, strategies for the development of antibiofilm agents, and their assessments. The review also revisits some selected peptides and polyketides from marine microbes reported between 2016 and 2023, highlighting their moderate and considerable antibiofilm activities. Moreover, their antibiofilm mechanisms, such as adhesion modulation/inhibition targeting biofilm-forming pathogens, quorum sensing intervention and inhibition, and extracellular polymeric substance disruption, are highlighted herein.

α,α-disubstituted β-amino amides eliminate Staphylococcus aureus biofilms by membrane disruption and biomass removal

Bacterial biofilms account for up to 80% of all infections and complicate successful therapies due to their intrinsic tolerance to antibiotics. Biofilms also cause serious problems in the industrial sectors, for instance due to the deterioration of metals or microbial contamination of products. Efforts are put in finding novel strategies in both avoiding and fighting biofilms. Biofilm control is achieved by killing and/or removing biofilm or preventing transition to the biofilm lifestyle. Previous research reported on the anti-biofilm potency of α,α-disubstituted β-amino amides A1, A2 and A3, which are small antimicrobial peptidomimetics with a molecular weight below 500 Da. In the current study it was investigated if these derivatives cause a fast disintegration of biofilm bacteria and removal of Staphylococcus aureus biofilms. One hour incubation of biofilms with all three derivatives resulted in reduced metabolic activity and membrane permeabilization in S. aureus (ATCC 25923) biofilms. Bactericidal properties of these derivatives were attributed to a direct effect on membranes of biofilm bacteria. The green fluorescence protein expressing Staphylococcus aureus strain AH2547 was cultivated in a CDC biofilm reactor and utilized for disinfectant efficacy testing of A3, following the single tube method (American Society for Testing and Materials designation number E2871). A3 at a concentration of 90 μM acted as fast as 100 μM chlorhexidine and was equally effective. Confocal laser scanning microscopy studies showed that chlorhexidine treatment lead to fluorescence fading indicating membrane permeabilization but did not cause biomass removal. In contrast, A3 treatment caused a simultaneous biofilm fluorescence loss and biomass removal. These dual anti-biofilm properties make α,α-disubstituted β-amino amides promising scaffolds in finding new control strategies against recalcitrant biofilms.

Recent Updates on the Antimicrobial Compounds from Marine-Derived Penicillium fungi

In this review, 72 compounds isolated from marine-derived Penicillium fungi and their antimicrobial activities are reviewed from 2020 to 2023. According to their structures, these compounds can be divided into terpenoids, polyketides, alkaloids and other structural compounds, among which terpenoids and polyketides are relatively large in number. Some compounds have powerful inhibitory effects against different pathogenic bacteria and fungi. This review aims to provide more useful information and enlightenment for further efficient utilization of Penicillium spp. and their secondary metabolites.

Synthesis of fusidane triterpenoid Mannich bases as potential antibacterial and antitumor agents

Mannich bases (8 examples) were synthesized via aminomethylation of fusidane propargyl esters. In vitro antimicrobial screening against key ESKAPE pathogens showed that the fusidic acid based Mannich products exhibit a high antimicrobial effect against Gram-positive bacteria Staphylococcus aureus and the fungus Cryptococcus neoformans. Moreover, the cytotoxic effect of fusidic acid and its analogs, which showed high antibacterial activity, was determined by MTT assay on cancer HepG2, HCT-116, SH-SY5Y, MCF-7, A549 and conditionally normal cells HEK293. A remarkable cytotoxic activity of fusidic acid propargyl ester and its aminomethylene derivatives against cancer and nontumoral HEK293 cells with IC50 values within 4.2-25 µM was found.

Reversing the biofilm-inducing effect of two xanthones from Garcinia mangostana by 3-methyl-2(5H)-furanone and N-butyryl-D-L homoserine lactone

BACKGROUND

According to the WHO, 12 bacteria cause numerous human infections, including Enterobacteriaceae Klebsiella pneumoniae, and thus represent a public health problem. Microbial resistance is associated with biofilm formation; therefore, it is critical to know the biofilm-inducing potential of various compounds of everyday life. Likewise, the reversibility of biofilms and the modulation of persister cells are important for controlling microbial pathogens. In this work, we investigated the biofilm-inducing effects of xanthones from Garcinia mangostana on Klebsiella pneumoniae. Furthermore, we investigated the reversal effect of 3-methyl-2(5H)-furanone and the formation of persister cells induced by xanthones and their role in modulating the biofilm to the antibiotic gentamicin.

METHODS

To analyze the biofilm-inducing role of xanthones from Garcinia mangostana, cultures of K. pneumoniae containing duodenal probe pieces were treated with 0.1-0.001 μM α- and γ-mangostin, and the biofilm levels were measured using spectrophotometry. To determine biofilm reversion, cultures treated with xanthones, or gentamicin were mixed with 3-methyl-2(5H)-furanone or N-butyryl-DL-homoserine lactone. The presence of K. pneumoniae persister cells was determined by applying the compounds to the mature biofilm, and the number of colony-forming units was counted.

RESULTS

The xanthones α- and γ-mangostin increased K. pneumoniae biofilm production by 40% with duodenal probes. However, 3-methyl-2(5H)-furanone at 0.001 μΜ reversed biofilm formation by up to 60%. Moreover, adding the same to a culture treated with gentamicin reduced the biofilm by 80.5%. This effect was highlighted when 3-methyl-2(5H)-furanone was administered 6 h later than xanthones. At high concentrations of α-mangostin, persister K. pneumoniae cells in the biofilm were about 5 - 10 times more abundant than cells, whereas, with γ-mangostin, they were about 100 times more.

CONCLUSION

Two xanthones, α- and γ-mangostin from G. mangostana, induced biofilm formation in K. pneumoniae and promoted persister cells. However, the biofilm formation was reversed by adding 3-methyl-2(5H)-furanone, and even this effect was achieved with gentamicin. In addition, this compound controlled the persister K. pneumoniae cells promoted by α-mangostin. Thus, synthetic, and natural biofilm-inducing compounds could harm human health. Therefore, avoiding these substances and looking for biofilm inhibitors would be a strategy to overcome microbial resistance and recover antibiotics that are no longer used.

Evolving biofilm inhibition and eradication in clinical settings through plant-based antibiofilm agents

BACKGROUND

After almost 100 years since evidence of biofilm mode of growth and decades of intensive investigation about their formation, regulatory pathways and mechanisms of antimicrobial tolerance, nowadays there are still no therapeutic solutions to eradicate bacterial biofilms and their biomedical related issues.

PURPOSE

This review intends to provide a comprehensive summary of the recent and most relevant published studies on plant-based products, or their isolated compounds with antibiofilm activity mechanisms of action or identified molecular targets against bacterial biofilms. The objective is to offer a new perspective of most recent data for clinical researchers aiming to prevent or eliminate biofilm-associated infections caused by bacterial pathogens.

METHODS

The search was performed considering original research articles published on PubMed, Web of Science and Scopus from 2015 to April 2023, using keywords such as "antibiofilm", "antivirulence", "phytochemicals" and "plant extracts".

RESULTS

Over 180 articles were considered for this review with a focus on the priority human pathogens listed by World Health Organization, including Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumoniae and Escherichia coli. Inhibition and detachment or dismantling of biofilms formed by these pathogens were found using plant-based extract/products or derivative compounds. Although combination of plant-based products and antibiotics were recorded and discussed, this topic is currently poorly explored and only for a reduced number of bacterial species.

CONCLUSIONS

This review clearly demonstrates that plant-based products or derivative compounds may be a promising therapeutic strategy to eliminate bacterial biofilms and their associated infections. After thoroughly reviewing the vast amount of research carried out over years, it was concluded that plant-based products are mostly able to prevent biofilm formation through inhibition of quorum sensing signals, but also to disrupt mature biofilms developed by multidrug resistant bacteria targeting the biofilm extracellular polymeric substance. Flavonoids and phenolic compounds seemed the most effective against bacterial biofilms.

Helicobacter pylori in the post-antibiotics era: from virulence factors to new drug targets and therapeutic agents

Helicobacter pylori is considered one of the most prevalent human pathogenic microbes globally. It is the main cause of a number of gastrointestinal ailments, including peptic and duodenal ulcers, and gastric tumors with high mortality rates. Thus, eradication of H. pylori is necessary to prevent gastric cancer. Still, the rise in antibiotic resistance is the most important challenge for eradication strategies. Better consideration of H. pylori virulence factors, pathogenesis, and resistance is required for better eradication rates and, thus, prevention of gastrointestinal malignancy. This article is aimed to show the role of virulence factors of H. pylori. Some are involved in its survival in the harsh environment of the human gastric lumen, and others are related to pathogenesis and the infection process. Furthermore, this work has highlighted the recent advancement in H. pylori treatment, as well as antibiotic resistance as a main challenge in H. pylori eradication. Also, we tried to provide an updated summary of the evolving H. pylori control strategies and the potential alternative drugs to fight this lethal resistant pathogen. Recent studies have focused on evaluating the efficacy of alternative regimens (such as sequential, hybrid, concomitant treatment, vonoprazan (VPZ)-based triple therapy, high-dose PPI-amoxicillin dual therapy, probiotics augmented triple therapy, or in combination with BQT) in the effective eradication of H. pylori. Thus, innovating new anti-H. pylori drugs and establishing H. pylori databanks are upcoming necessities in the near future.

Natural cordiaquinones as strategies to inhibit the growth and biofilm formation of methicillin-sensitive and methicillin-resistant Staphylococcus spp

AIMS

The aim of this study was to investigate the antibacterial and antibiofilm potential of cordiaquinones B, E, L, N, and O against different Staphylococci strains, in addition to analyzing in silico the observed effect.

METHODS AND RESULTS

The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were determined according to CLSI guidelines. The inhibition of biofilm formation was investigated at sub-MICs. Atomic force microscopy (AFM) and density functional theory method were performed. The tested strains of Staphylococcus spp. were susceptible to cordiaquinones B, E, and L, among which cordiaquinone B exerted a bactericidal effect, confirmed by a bacterial growth curve study, against Staphylococcus saprophyticus. Cordiaquinones B and E showed lowest MBC values against S. saprophyticus. AFM revealed that cordiaquinone L reduced the mean cell size of S. saprophyticus. Cordiaquinones B and E inhibited the biofilm formation ability of S. aureus by ∼90%. The in silico analysis suggested that the antimicrobial activity of cordiaquinones is driven by their electron donation capability.

CONCLUSIONS

Cordiaquinones inhibit the growth and biofilm formation (virulence factor) of both methicillin-sensitive and methicillin-resistant Staphylococci strains, indicating their antimicrobial potential.

Recent advances in the discovery of plant-derived antimicrobial natural products to combat antimicrobial resistant pathogens: insights from 2018-2022

Covering: 2018 to 2022Antimicrobial resistance (AMR) poses a significant global health threat. There is a rising demand for innovative drug scaffolds and new targets to combat multidrug-resistant bacteria. Before the advent of antibiotics, infections were treated with plants chosen from traditional medicine practices. Of Earth's 374 000 plant species, approximately 9% have been used medicinally, but most species remain to be investigated. This review illuminates discoveries of antimicrobial natural products from plants covering 2018 to 2022. It highlights plant-derived natural products with antibacterial, antivirulence, and antibiofilm activity documented in lab studies. Additionally, this review examines the development of novel derivatives from well-studied parent natural products, as natural product derivatives have often served as scaffolds for anti-infective agents.

Photoredox-catalyzed diastereoselective dearomative prenylation and reverse-prenylation of electron-deficient indole derivatives

Prenylated and reverse-prenylated indolines are privileged scaffolds in numerous naturally occurring indole alkaloids with a broad spectrum of important biological properties. Development of straightforward and stereoselective methods to enable the synthesis of structurally diverse prenylated and reverse-prenylated indoline derivatives is highly desirable and challenging. In this context, the most direct approaches to achieve this goal generally rely on transition-metal-catalyzed dearomative allylic alkylation of electron-rich indoles. However, the electron-deficient indoles are much less explored, probably due to their diminished nucleophilicity. Herein, a photoredox-catalyzed tandem Giese radical addition/Ireland-Claisen rearrangement is disclosed. Diastereoselective dearomative prenylation and reverse-prenylation of electron-deficient indoles proceed smoothly under mild conditions. An array of tertiary α-silylamines as radical precursors is readily incorporated in 2,3-disubstituted indolines with high functional compatibility and excellent diastereoselectivity (>20:1 d.r.). The corresponding transformations of the secondary α-silylamines provide the biologically important lactam-fused indolines in one-pot synthesis. Subsequently, a plausible photoredox pathway is proposed based on control experiments. The preliminary bioactivity study reveals a potential anticancer property of these structurally appealing indolines.

Delving into the Mechanisms of Sponge-Associated Enterobacter against Staphylococcal Biofilms

Staphylococci are one of the most common causes of biofilm-related infections. Such infections are hard to treat with conventional antimicrobials, which often lead to bacterial resistance, thus being associated with higher mortality rates while imposing a heavy economic burden on the healthcare system. Investigating antibiofilm strategies is an area of interest in the fight against biofilm-associated infections. Previously, a cell-free supernatant from marine-sponge-associated Enterobacter sp. inhibited staphylococcal biofilm formation and dissociated the mature biofilm. This study aimed to identify the chemical components responsible for the antibiofilm activity of Enterobacter sp. Scanning electron microscopy confirmed that the aqueous extract at the concentration of 32 μg/mL could dissociate the mature biofilm. Liquid chromatography coupled with high-resolution mass spectrometry revealed seven potential compounds in the aqueous extract, including alkaloids, macrolides, steroids, and triterpenes. This study also suggests a possible mode of action on staphylococcal biofilms and supports the potential of sponge-derived Enterobacter as a source of antibiofilm compounds.

Mechanistic Insights into the Antibiofilm Mode of Action of Ellagic Acid

Bacterial biofilm is a major contributor to the persistence of infection and the limited efficacy of antibiotics. Antibiofilm molecules that interfere with the biofilm lifestyle offer a valuable tool in fighting bacterial pathogens. Ellagic acid (EA) is a natural polyphenol that has shown attractive antibiofilm properties. However, its precise antibiofilm mode of action remains unknown. Experimental evidence links the NADH:quinone oxidoreductase enzyme WrbA to biofilm formation, stress response, and pathogen virulence. Moreover, WrbA has demonstrated interactions with antibiofilm molecules, suggesting its role in redox and biofilm modulation. This work aims to provide mechanistic insights into the antibiofilm mode of action of EA utilizing computational studies, biophysical measurements, enzyme inhibition studies on WrbA, and biofilm and reactive oxygen species assays exploiting a WrbA-deprived mutant strain of Escherichia coli. Our research efforts led us to propose that the antibiofilm mode of action of EA stems from its ability to perturb the bacterial redox homeostasis driven by WrbA. These findings shed new light on the antibiofilm properties of EA and could lead to the development of more effective treatments for biofilm-related infections.

Liposomes-Based Drug Delivery Systems of Anti-Biofilm Agents to Combat Bacterial Biofilm Formation

All currently approved antibiotics are being met by some degree of resistance by the bacteria they target. Biofilm formation is one of the crucial enablers of bacterial resistance, making it an important bacterial process to target for overcoming antibiotic resistance. Accordingly, several drug delivery systems that target biofilm formation have been developed. One of these systems is based on lipid-based nanocarriers (liposomes), which have shown strong efficacy against biofilms of bacterial pathogens. Liposomes come in various types, namely conventional (charged or neutral), stimuli-responsive, deformable, targeted, and stealth. This paper reviews studies employing liposomal formulations against biofilms of medically salient gram-negative and gram-positive bacterial species reported recently. When it comes to gram-negative species, liposomal formulations of various types were reported to be efficacious against Pseudomonas aeruginosa, Escherichia coli, Acinetobacter baumannii, and members of the genera Klebsiella, Salmonella, Aeromonas, Serratia, Porphyromonas, and Prevotella. A range of liposomal formulations were also effective against gram-positive biofilms, including mostly biofilms of Staphylococcal strains, namely Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus saprophyticus subspecies bovis, followed by Streptococcal strains (pneumonia, oralis, and mutans), Cutibacterium acnes, Bacillus subtilis, Mycobacterium avium, Mycobacterium avium subsp. hominissuis, Mycobacterium abscessus, and Listeria monocytogenes biofilms. This review outlines the benefits and limitations of using liposomal formulations as means to combat different multidrug-resistant bacteria, urging the investigation of the effects of bacterial gram-stain on liposomal efficiency and the inclusion of pathogenic bacterial strains previously unstudied.

Synthesis and Evaluation of Piperazine-Tethered Derivatives of Alepterolic Acid as Anticancer Agents

Alepterolic acid is a natural diterpenoid isolated from Aleuritopteris argentea with potential anti-cancer activity. In this study, alepterolic acid was modified to construct a series of arylformyl piperazinyl derivatives (3a-3p). The synthesized derivatives were fully characterized with HRMS, NMR, and IR. Four compounds with inhibition rate higher than 30 % at 10 μM (3f, 3n, 3g and 3k) were further measured to obtain the IC50 values against four cancer cell lines, including hepatoma cell lines HepG2, lung cancer cell lines A549, estrogen receptor-positive cell lines MCF7, and triple-negative breast cancer (TNBC) cell lines MDA-MB-231 by MTT assay. It was found that these compounds were more effective to HepG2 and MDA-MB-231 cells, while less toxic to A549 and MCF7 cells, and compound 3n as the most toxic derivatve against MDA-MB-231 cell lines, with IC50 value of 5.55±0.56 μM. Trypan blue staining and colony formation assay showed that compound 3n inhibited the growth of MDA-MB-231 cells and prevented colony formation. Hoechst staining, flow cytometry and western blot analysis revealed that compound 3n induced caspase-dependent apoptosis in MDA-MB-231 cells. Conclusively, compound 3n was demonstrated to be a potential anti-cancer lead compound for further investigation.

Protecting-Group-Free Synthesis of Meridianin A-G and Derivatives and Its Antibiofilm Evaluation

Herein, a protecting-group-free protocol was developed to realize a time and step economy diversification of the Meridianin alkaloid. A broad range of substituents are tolerated to deliver the products in moderate to high yields, and the first synthesis of Meridianin B was achieved. The simplicity of this protocol enables the rapid construction of a Meridianin derivative library for antibiofilm evaluation. Preliminary results reveal that Meridianin derivatives were capable of inhibiting the Acinetobacter baumannii biofilm and lowering the antibiotic MIC synergistically.

Targeted pH-responsive chitosan nanogels with Tanshinone IIA for enhancing the antibacterial/anti-biofilm efficacy

Persistent bacterial infection caused by biofilms is one of the most serious problems that threatened human health. The development of antibacterial agents remains a challenge to penetrate biofilm and effectively treat the underlying bacterial infection. In the current study, chitosan-based nanogels were developed for encapsulating the Tanshinone IIA (TA) to enhance the antibacterial and anti-biofilm efficacy against Streptococcus mutans (S. mutans). The as-prepared nanogels (TA@CS) displayed excellent encapsulation efficiency (91.41 ± 0.11 %), uniform particle sizes (393.97 ± 13.92 nm), and enhanced positive potential (42.27 ± 1.25 mV). After being coated with CS, the stability of TA under light and other harsh environments was greatly improved. In addition, TA@CS displayed pH responsiveness, allowing it to selectively release more TA in acidic conditions. Furthermore, the positively charged TA@CS were equipped to target negatively charged biofilm surfaces and efficiently penetrate through biofilm barriers, making it promising for remarkable anti-biofilm activity. More importantly, when TA was encapsulated into CS nanogels, the antibacterial activity of TA was enhanced at least 4-fold. Meanwhile, TA@CS inhibited 72 % of biofilm formation at 500 μg/mL. The results demonstrated that the nanogels constituted CS and TA had antibacterial/anti-biofilm properties with synergistic enhanced effects, which will benefit pharmaceutical, food, and other fields.

Optimized Extraction, Identification and Anti-Biofilm Action of Wu Wei Zi (Fructus Schisandrae Chinensis) Extracts against Vibrio parahaemolyticus

The pathogenicity of foodborne Vibrio parahaemolyticus is a major concern for global public health. This study aimed to optimize the liquid-solid extraction of Wu Wei Zi extracts (WWZE) against Vibrio parahaemolyticus, identify its main components, and investigate the anti-biofilm action. The extraction conditions optimized by the single-factor test and response surface methodology were ethanol concentration of 69%, temperature at 91 °C, time of 143 min, and liquid-solid ratio of 20:1 mL/g. After high performance liquid chromatography (HPLC) analysis, it was found that the main active ingredients of WWZE were schisandrol A, schisandrol B, schisantherin A, schisanhenol, and schisandrin A-C. The minimum inhibitory concentration (MIC) of WWZE, schisantherin A, and schisandrol B measured by broth microdilution assay was 1.25, 0.625, and 1.25 mg/mL, respectively, while the MIC of the other five compounds was higher than 2.5 mg/mL, indicating that schisantherin A and schizandrol B were the main antibacterial components of WWZE. Crystal violet, Coomassie brilliant blue, Congo red plate, spectrophotometry, and Cell Counting Kit-8 (CCK-8) assays were used to evaluate the effect of WWZE on the biofilm of V. parahaemolyticus. The results showed that WWZE could exert its dose-dependent potential to effectively inhibit the formation of V. parahaemolyticus biofilm and clear mature biofilm by significantly destroying the cell membrane integrity of V. parahaemolyticus, inhibiting the synthesis of intercellular polysaccharide adhesin (PIA), extracellular DNA secretion, and reducing the metabolic activity of biofilm. This study reported for the first time the favorable anti-biofilm effect of WWZE against V. parahaemolyticus, which provides a basis for deepening the application of WWZE in the preservation of aquatic products.

β-Lactams from the Ocean

The title of this essay is as much a question as it is a statement. The discovery of the β-lactam antibiotics-including penicillins, cephalosporins, and carbapenems-as largely (if not exclusively) secondary metabolites of terrestrial fungi and bacteria, transformed modern medicine. The antibiotic β-lactams inactivate essential enzymes of bacterial cell-wall biosynthesis. Moreover, the ability of the β-lactams to function as enzyme inhibitors is of such great medical value, that inhibitors of the enzymes which degrade hydrolytically the β-lactams, the β-lactamases, have equal value. Given this privileged status for the β-lactam ring, it is therefore a disappointment that the exemplification of this ring in marine secondary metabolites is sparse. It may be that biologically active marine β-lactams are there, and simply have yet to be encountered. In this report, we posit a second explanation: that the value of the β-lactam to secure an ecological advantage in the marine environment might be compromised by its close structural similarity to the β-lactones of quorum sensing. The steric and reactivity similarities between the β-lactams and the β-lactones represent an outside-of-the-box opportunity for correlating new structures and new enzyme targets for the discovery of compelling biological activities.

Depsipeptides Targeting Tumor Cells: Milestones from In Vitro to Clinical Trials

Cancer is currently considered one of the most threatening diseases worldwide. Diet could be one of the factors that can be enhanced to comprehensively address a cancer patient's condition. Unfortunately, most molecules capable of targeting cancer cells are found in uncommon food sources. Among them, depsipeptides have emerged as one of the most reliable choices for cancer treatment. These cyclic amino acid oligomers, with one or more subunits replaced by a hydroxylated carboxylic acid resulting in one lactone bond in a core ring, have broadly proven their cancer-targeting efficacy, some even reaching clinical trials and being commercialized as "anticancer" drugs. This review aimed to describe these depsipeptides, their reported amino acid sequences, determined structure, and the specific mechanism by which they target tumor cells including apoptosis, oncosis, and elastase inhibition, among others. Furthermore, we have delved into state-of-the-art in vivo and clinical trials, current methods for purification and synthesis, and the recognized disadvantages of these molecules. The information collated in this review can help researchers decide whether these molecules should be incorporated into functional foods in the near future.

Innovative Strategies to Overcome Antimicrobial Resistance and Tolerance

Antimicrobial resistance and tolerance are natural phenomena that arose due to evolutionary adaptation of microorganisms against various xenobiotic agents. These adaptation mechanisms make the current treatment options challenging as it is increasingly difficult to treat a broad range of infections, associated biofilm formation, intracellular and host adapted microbes, as well as persister cells and microbes in protected niches. Therefore, novel strategies are needed to identify the most promising drug targets to overcome the existing hurdles in the treatment of infectious diseases. Furthermore, discovery of novel drug candidates is also much needed, as few novel antimicrobial drugs have been introduced in the last two decades. In this review, we focus on the strategies that may help in the development of innovative small molecules which can interfere with microbial resistance mechanisms. We also highlight the recent advances in optimization of growth media which mimic host conditions and genome scale molecular analyses of microbial response against antimicrobial agents. Furthermore, we discuss the identification of antibiofilm molecules and their mechanisms of action in the light of the distinct physiology and metabolism of biofilm cells. This review thus provides the most recent advances in host mimicking growth media for effective drug discovery and development of antimicrobial and antibiofilm agents.

A Review: Meridianins and Meridianins Derivatives

Meridianins are a family of indole alkaloids derived from Antarctic tunicates with extensive pharmacological activities. A series of meridianin derivatives had been synthesized by drug researchers. This article reviews the extraction and purification methods, biological activities and pharmacological applications, pharmacokinetic characters and chemical synthesis of meridianins and their derivatives. And prospects on discovering new bioactivities of meridianins and optimizing their structure for the improvement of the ADMET properties are provided.

Metabolomic and Proteomic Changes in Candida albicans Biofilm in Response to Zosteric Acid Treatment

Zosteric acid (ZA) is a secondary metabolite of the seagrass Zostera marina, with antibiofilm activity against fungi. Information concerning its mechanisms of action is lacking and this limits the development of more potent derivatives based on the same target and activity structure. The aim of this work was to investigate the ZA mode of action by analyzing the metabolic status of Candida albicans biofilm and its protein expression profile upon ZA treatment. Fourier-Transform Infrared Spectroscopy confirmed that ZA modified the metabolomic response of treated cells, showing changes in the spectral regions, mainly related to the protein compartment. Nano Liquid Chromatography-High-Resolution Mass Spectrometry highlighted that 10 proteins were differentially expressed in the C. albicans proteome upon ZA treatment. Proteins involved in the biogenesis, structure and integrity of cell walls as well as adhesion and stable attachment of hyphae were found downregulated, whereas some proteins involved in the stress response were found overexpressed. Additionally, ZA was involved in the modulation of non-DNA-based epigenetic regulatory mechanisms triggered by reactive oxygen species. These results partially clarified the ZA mechanism of action against fungi and provided insight into the major C. albicans pathways responsible for biofilm formation.

In Silico Identification of Potential Insect Peptides against Biofilm-Producing Staphylococcus aureus

Biofilm-producing Staphylococcus aureus (SA) strains are frequently found in medical environments, from surgical/ wound sites, medical devices. These biofilms reduce the efficacy of applied antibiotics during the treatment of several infections, such as cystic fibrosis, endocarditis, or urinary tract infections. Thus, the development of potential therapeutic agents to destroy the extra protective biofilm layers or to inhibit the biofilm-producing enzymes is urgently needed. Advanced and cost-effective bioinformatics tools are advantageous in locating and speeding up the selection of antibiofilm candidates. Based on the potential drug characteristics, we have selected one-hundred thirty-three antibacterial peptides derived from insects to assess for their antibiofilm potency via molecular docking against five putative biofilm formation and regulated target enzymes: the staphylococcal accessory regulator A or SarA (PDB ID: 2FRH), 4,4'-diapophytoene synthase or CrtM (PDB ID: 2ZCQ), clumping factor A or ClfA (PDB ID: 1N67) and serine-aspartate repeat protein C or SdrC (PDB ID: 6LXH) and sortase A or SrtA (PDB ID: 1T2W) of SA bacterium. In this study, molecular docking was performed using HPEPDOCK and HDOCK servers, and molecular interactions were examined using BIOVIA Discovery Studio Visualizer-2019. The docking score (kcal/mol) range of five promising antibiofilm peptides against five targets was recorded as follows: diptericin A (-215.52 to -303.31), defensin (-201.11 to -301.92), imcroporin (-212.08 to -287.64), mucroporin (-228.72 to -286.76), apidaecin II (-203.90 to -280.20). Among these five, imcroporin and mucroporin were 13 % each, while defensin contained only 1 % of positive net charged residues (Arg+Lys) projected through ProtParam and NetWheels tools. Similarly, imcroporin, mucroporin and apidaecin II were 50 %, while defensin carried 21.05 % of hydrophobic residues predicted by the tool PEPTIDE. 2.0. Most of the peptides exhibited potential characteristics to inhibit S. aureus-biofilm formation via disrupting the cell membrane and cytoplasmic integrity. In summary, the proposed hypothesis can be considered a cost-effective platform for selecting the most promising bioactive drug candidates within a limited timeframe with a greater chance of success in experimental and clinical studies.

Seaweed Extracts as an Effective Gateway in the Search for Novel Antibiofilm Agents against Staphylococcus aureus

Treatment of biofilm-associated infections has become a major challenge in biomedical and clinical fields due to the failure of conventional treatments in controlling this highly complex and tolerant structure. Therefore, the search for novel antibiofilm agents with increased efficacy as those provided by natural products, presents an urgent need. The aim of this study was to explore extracts derived from three algae (green Ulva lactuca, brown Stypocaulon scoparium, red Pterocladiella capillacea) for their potential antibiofilm activity against Staphylococcus aureus, bacterium responsible for several acute and chronic infections. Seaweed extracts were prepared by successive maceration in various solvents (cyclohexane (CH), dichloromethane (DCM), ethyl acetate (EA), and methanol (MeOH)). The ability of the different extracts to inhibit S. aureus biofilm formation was assessed using colony-forming unit (CFU) counts method supported by epifluorescence microscopic analysis. Effects of active extracts on the biofilm growth cycle, as well as on S. aureus surface hydrophobicity were evaluated. Results revealed the ability of four extracts to significantly inhibit S. aureus biofilm formation. These findings were supported by microscopy analyses. The gradual increase in the number of adherent bacteria when the selected extracts were added at various times (t₀, t_2h, t_4h, t_6h, and t_24h) revealed their potential effect on the initial adhesion and proliferation stages of S. aureus biofilm development. Interestingly, a significant reduction in the surface hydrophobicity of S. aureus treated with dichloromethane (DCM) extract derived from U. lactuca was demonstrated. These findings present new insights into the exploration of seaweeds as a valuable source of antibiofilm agents with preventive effect by inhibiting and/or delaying biofilm formation.

Natural products from traditional medicine as promising agents targeting at different stages of oral biofilm development

Oral cavity is an ideal habitat for more than 1,000 species of microorganisms. The diverse oral microbes form biofilms over the hard and soft tissues in the oral cavity, affecting the oral ecological balance and the development of oral diseases, such as caries, apical periodontitis, and periodontitis. Currently, antibiotics are the primary agents against infectious diseases; however, the emergence of drug resistance and the disruption of oral microecology have challenged their applications. The discovery of new antibiotic-independent agents is a promising strategy against biofilm-induced infections. Natural products from traditional medicine have shown potential antibiofilm activities in the oral cavity with high safety, cost-effectiveness, and minimal adverse drug reactions. Aiming to highlight the importance and functions of natural products from traditional medicine against oral biofilms, here we summarized and discussed the antibiofilm effects of natural products targeting at different stages of the biofilm formation process, including adhesion, proliferation, maturation, and dispersion, and their effects on multi-species biofilms. The perspective of antibiofilm agents for oral infectious diseases to restore the balance of oral microecology is also discussed.

Biofilms as a microbial hazard in the food industry: A scoping review

Biofilms pose a serious public health hazard with a significant economic impact on the food industry. The present scoping review is designed to analyze the literature published during 2001-2020 on biofilm formation of microbes, their detection methods, and association with antimicrobial resistance (if any). The peer-reviewed articles retrieved from 04 electronic databases were assessed using PRISMA-ScR guidelines. From the 978 preliminary search results, a total of 88 publications were included in the study. On analysis, the commonly isolated pathogens were Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., Escherichia coli, Bacillus spp., Vibrio spp., Campylobacter jejuni and Clostridium perfringens. The biofilm-forming ability of microbes was found to be influenced by various factors such as attachment surfaces, temperature, presence of other species, nutrient availability etc. A total of 18 studies characterized the biofilm-forming genes, particularly for S. aureus, Salmonella spp., and E. coli. In most studies, polystyrene plate and/or stainless-steel coupons were used for biofilm formation, and the detection was carried out by crystal violet assays and/or by plate counting method. The strain-specific significant differences in biofilm formation were observed in many studies, and few studies carried out analysis of multi-species biofilms. The association between biofilm formation and antimicrobial resistance wasn't clearly defined. Further, viable but non-culturable (VBNC) form of the foodborne pathogens is posing an unseen (by conventional cultivation techniques) but potent threat food safety. The present review recommends the need for carrying out systematic surveys and risk analysis of biofilms in food chain to highlight the evidence-based public health concerns, especially in regions where microbiological food hazards are quite prevalent.

The potential application of natural products in cutaneous wound healing: A review of preclinical evidence

Under normal circumstances, wound healing can be summarized as three processes. These include inflammation, proliferation, and remodeling. The vast majority of wounds heal rapidly; however, a large percentage of nonhealing wounds have still not been studied significantly. The factors affecting wound nonhealing are complex and diverse, and identifying an effective solution from nature becomes a key goal of research. This study aimed to highlight and review the mechanisms and targets of natural products (NPs) for treating nonhealing wounds. The results of relevant studies have shown that the effects of NPs are associated with PI3K-AKT, P38MAPK, fibroblast growth factor, MAPK, and ERK signaling pathways and involve tumor growth factor (TNF), vascular endothelial growth factor, TNF-α, interleukin-1β, and expression of other cytokines and proteins. The 25 NPs that contribute to wound healing were systematically summarized by an inductive collation of the six major classes of compounds, including saponins, polyphenols, flavonoids, anthraquinones, polysaccharides, and others, which will further direct the attention to the active components of NPs and provide research ideas for further development of new products for wound healing.

Helicobacter pylori Biofilm-Related Drug Resistance and New Developments in Its Anti-Biofilm Agents

Helicobacter pylori is one of the most common pathogenic bacterium worldwide, infecting about 50% of the world’s population. It is a major cause of several upper gastrointestinal diseases, including peptic ulcers and gastric cancer. The emergence of H. pylori resistance to antibiotics has been a major clinical challenge in the field of gastroenterology. In the course of H. pylori infection, some bacteria invade the gastric epithelium and are encapsulated into a self-produced matrix to form biofilms that protect the bacteria from external threats. Bacteria with biofilm structures can be up to 1000 times more resistant to antibiotics than planktonic bacteria. This implies that targeting biofilms might be an effective strategy to alleviate H. pylori drug resistance. Therefore, it is important to develop drugs that can eliminate or disperse biofilms. In recent years, anti-biofilm agents have been investigated as alternative or complementary therapies to antibiotics to reduce the rate of drug resistance. This article discusses the formation of H. pylori biofilms, the relationship between biofilms and drug resistance in H. pylori, and the recent developments in the research of anti-biofilm agents targeting H. pylori drug resistance.

Pyocyanin Modulates Gastrointestinal Transformation and Microbiota

Phenazines are ubiquitously produced by Pseudomonas spp. in the environment and are widely used in agriculture and clinical therapies, making their accumulation through the food chain cause potential risks to human health. Here, we utilized pyocyanin (PYO) as a representative to study the effects of phenazines on digestive tracts. Pharmacokinetic analysis showed that PYO exhibited low systemic exposure, slow elimination, and low accumulation in both rat and pig models. PYO was subsequently found to induce intestinal microbiota dysbiosis, destroy the mucus layer and physical barrier, and even promote gut vascular barrier (GVB) impairment, consequently increasing the gut permeability. Additionally, integral and metabolomic analyses of the liver demonstrated that PYO induced liver inflammation and metabolic disorders. The metabolic analysis further confirmed that all of the metabolites of PYO retain the nitrogen-containing tricyclic structural skeleton of phenazines, which was the core bioactivity of phenazine compounds. These findings elucidated that PYO could be metabolized by animals. Meanwhile, high levels of PYO could induce intestinal barrier impairment and liver damage, suggesting that we should be alert to the accumulation of phenazines.

Modular Synthetic Routes to Fluorine-Containing Halogenated Phenazine and Acridine Agents That Induce Rapid Iron Starvation in Methicillin-Resistant Staphylococcus aureus Biofilms

During infection, bacteria use an arsenal of resistance mechanisms to negate antibiotic therapies. In addition, pathogenic bacteria form surface-attached biofilms bearing enriched populations of metabolically dormant persister cells. Bacteria develop resistance in response to antibiotic insults; however, nonreplicating biofilms are innately tolerant to all classes of antibiotics. As such, molecules that can eradicate antibiotic-resistant and antibiotic-tolerant bacteria are of importance. Here, we report modular synthetic routes to fluorine-containing halogenated phenazine (HP) and halogenated acridine (HA) agents with potent antibacterial and biofilm-killing activities. Nine fluorinated phenazines were rapidly accessed through a synthetic strategy involving (1) oxidation of fluorinated anilines to azobenzene intermediates, (2) S_NAr with 2-methoxyaniline, and (3) cyclization to phenazines upon treatment with trifluoroacetic acid. Five structurally related acridine heterocycles were synthesized using S_NAr and Buchwald-Hartwig approaches. From this focused collection, phenazines 5g, 5h, 5i, and acridine 9c demonstrated potent antibacterial activities against Gram-positive pathogens (MIC = 0.04-0.78 μM). Additionally, 5g and 9c eradicated Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis biofilms with excellent potency (5g, MBEC = 4.69-6.25 μM; 9c, MBEC = 4.69-50 μM). Using real-time quantitative polymerase chain reaction (RT-qPCR), 5g, 5h, 5i, and 9c rapidly induce the transcription of iron uptake biomarkers isdB and sbnC in methicillin-resistant S. aureus (MRSA) biofilms, and we conclude that these agents operate through iron starvation. Overall, fluorinated phenazine and acridine agents could lead to ground-breaking advances in the treatment of challenging bacterial infections.

Anti-Larval and Anti-Algal Natural Products from Marine Microorganisms as Sources of Anti-Biofilm Agents

Bacteria growing inside biofilms are more resistant to hostile environments, conventional antibiotics, and mechanical stresses than their planktonic counterparts. It is estimated that more than 80% of microbial infections in human patients are biofilm-based, and biofouling induced by the biofilms of some bacteria causes serious ecological and economic problems throughout the world. Therefore, exploring highly effective anti-biofilm compounds has become an urgent demand for the medical and marine industries. Marine microorganisms, a well-documented and prolific source of natural products, provide an array of structurally distinct secondary metabolites with diverse biological activities. However, up to date, only a handful of anti-biofilm natural products derived from marine microorganisms have been reported. Meanwhile, it is worth noting that some promising antifouling (AF) compounds from marine microbes, particularly those that inhibit settlement of fouling invertebrate larvae and algal spores, can be considered as potential anti-biofilm agents owing to the well-known knowledge of the correlations between biofilm formation and the biofouling process of fouling organisms. In this review, a total of 112 anti-biofilm, anti-larval, and anti-algal natural products from marine microbes and 26 of their synthetic analogues are highlighted from 2000 to 2021. These compounds are introduced based on their microbial origins, and then categorized into the following different structural groups: fatty acids, butenolides, terpenoids, steroids, phenols, phenyl ethers, polyketides, alkaloids, flavonoids, amines, nucleosides, and peptides. The preliminary structure-activity relationships (SAR) of some important compounds are also briefly discussed. Finally, current challenges and future research perspectives are proposed based on opinions from many previous reviews.