Tackling Antibiotic Resistance with Compounds of Natural Origin: A Comprehensive Review

Aqueous extracts of Moringa oleifera and Cinnamomum cassia as promising sources of antibiofilm compounds against mucoid and small colony variants of Pseudomonas aeruginosa and Staphylococcus aureus

Bacterial biofilms formed by Staphylococcus aureus and Pseudomonas aeruginosa pose significant challenges in treating cystic fibrosis (CF) airway infections due to their resistance to antibiotics. New therapeutic approaches are urgently needed to treat these chronic infections. This study aimed to investigate the antibiofilm potential of various plant extracts, specifically targeting mucoid and small colony variants of P. aeruginosa and S. aureus and strains. Moreover, it aimed to gain insights into the mechanisms of action and the potential phytochemicals responsible for antibiofilm activity. Solid-liquid extractions were performed on seven biomasses using water and ethanol (70 and 96 %) under controlled conditions, resulting in 21 distinct plant extracts. These extracts were evaluated for extraction yield, antioxidant activity, phenolic content, chemical composition by HPLC-TOF-MS, and antibiofilm activity using a 96-well plate assay, followed by crystal violet staining, bacterial adhesion assessment, and brightfield microscopy. Our findings revealed that aqueous extracts exhibited the highest inhibition of biofilm formation, with cinnamon bark and moringa seeds showing strong antibiofilm activity against both bacterial species. Brightfield microscopy confirmed that these extracts effectively inhibited biofilm formation. Chemical analysis identified key bioactive compounds, including moringin, benzaldehyde, coumarin, and quinic acid, which likely contribute to the observed antibiofilm effects. Recognizing that the antibiofilm properties of moringin, a common compound in both moringa seed and cinnamon bark extracts, remain underexplored, we conducted potential target identification via PharmMapper and molecular docking analyses to provide a foundation for future research. Computational analyses indicated that moringin might inhibit aspartate-semialdehyde dehydrogenase in P. aeruginosa and potentially interact with an unknown target in S. aureus. In conclusion, moringa seed and cinnamon bark extracts demonstrated significant potential for developing new therapies targeting biofilm-associated infections in CF. Further studies are needed to validate the computational predictions, identify the bacterial targets, and elucidate the precise mechanisms behind moringin's antibiofilm activity, which is likely the potential key contributor to the observed activity of the moringa and cinnamon bark extracts.

Hybrid structure combining essential oil derivatives and polydopamine for anti-bacterial coatings

The development of effective antimicrobial surfaces is crucial for reducing the risk of medical device-associated infections. This study investigates the antibacterial potential of carvacrol (CAR), a natural essential oil, after their surface immobilization onto gold (Au) substrates through a polydopamine (pDA) layer. The successful deposition and properties of each layer were characterized using ellipsometry, water contact angle (WCA) measurements, Fourier Transform Infrared Reflection-Absorption Spectroscopy (FT-IRRAS), X-ray Photoelectron Spectroscopy (XPS), and Atomic Force Microscopy (AFM). The resulting coatings displayed a thin, uniform film with smooth topography and with enhanced hydrophilicity. Antibacterial efficacy was assessed against Staphylococcus epidermidis, a relevant etiological agent in this context. The results revealed that the polydopamine-carvacrol coated surfaces (Au-pDA-CAR) exhibited a significant reduction in bacterial viability, achieving a 96 % decrease compared to unmodified gold surfaces. This was contrasted with minimal antibacterial activity from surfaces with either only polydopamine (Au-pDA) or carvacrol (Au-CAR). Live/Dead bacterial viability assays confirmed the bactericidal effect of the Au-pDA-CAR surface, demonstrating its effectiveness in killing bacteria rather than merely preventing adhesion. Our findings indicate that the pDA-CAR coating presents a promising approach for developing antimicrobial surfaces with enhanced performance against biofilm-forming pathogens. The development of this coating is an important step towards the establishment of a new technological platform capable of preventing medical device associated infections.

Helicid: A novel Anti-Staphylococcus aureus adjuvant

Staphylocoagulase (Coa) plays a critical role in the pathogenicity of Staphylococcus aureus (S. aureus). The present study was undertaken to investigate the underlying mechanism which helicid (HEL) suppressed the virulence factor Coa, as well as to assess the synergistic inhibitory effects of HEL in conjunction with antibiotics, thereby establishing the potential of HEL as an antibacterial adjuvant. We employed coagulation and biofilm assays to comprehensively assess the inhibitory impact of HEL on S. aureus pathogenicity. The thermal shift assay demonstrated that HEL exerted a direct impact on the protein stability of Coa, evidenced by a 6 °C change in melting temperature (ΔTm) at a concentration of 100 μM. HEL binding to Coa proteins was further validated by molecular dynamics simulations and fluorescence quenching. Molecular docking and point mutation assays identified S23 and D112 as crucial binding sites for HEL and Coa. Furthermore, HEL has been observed to potentiate the bactericidal properties of ceftaroline fosamil (CEF-F), concurrently diminishing the resistance exhibited by S. aureus towards CEF-F, as demonstrated by antibiotic synergy tests and resistance induction assays. The combination of HEL and CEF-F effectively reduced the number of bacteria and improved the survival of both Galleria mellonella larvae and mice. Additionally, a significant decrease was observed in the levels of TNF-α, IL-6, and IFN-γ in mice broncho-alveolar lavage fluid (BALF). Ultimately, our findings confirmed that the direct binding of HEL to Coa could diminish the pathogenicity of S. aureus. Moreover, the combination with CEF-F substantially reduced the lethality associated with S. aureus-infected pneumonia and extended the efficacy of the antibiotic.

Prodigiosin Loaded SN-PB@PG NPs-Based Multimodal Therapy for the Healing of Bacterial Infected Chronic Wounds

Healing of infected chronic wounds faces dual challenges: persistent inflammation and impaired angiogenesis. To address these, SN-PB@PG nanocomplexes were prepared by hybridisation of nitroprusside (SNP) with Prussian blue (SN-PB NPs) and loaded with prodigiosin (PG). Under near-infrared (NIR) irradiation, SN-PB NPs generated mild hyperthermia, facilitating the release of nitric oxide (NO) and PG to combat bacterial biofilms and multidrug-resistant pathogens. The in vivo assay using diabetic infected wounds demonstrated that SN-PB@PG NPs with NIR reduced the wound area to 10.6% by the 11th day, which is superior to that of control group (29.6%). In the flap transplantation experiments, the data showed SN-PB@PG NPs with NIR group only have a necrobiosis of 3.8% of flaps on the 8th day, which is superior to 31.3% of the control group. Additionally, the release of NO promoted vascular regeneration by up-regulating vascular endothelial growth factor (VEGF) and platelet endothelial cell adhesion molecule-1 (CD31), and regenerated sarcomeric tissue by down-regulating MMP-9. The results indicated that the combination of SN-PB@PG NPs with gas and photothermal therapy exerted a combined antibacterial and wound healing effect. Compared to traditional clinical methods such as surgical debridement and hyperbaric oxygen therapy, this new strategy efficiently addresses issues of infection and healing, which is convenient for clinical application.

Phytochemical Insights and Therapeutic Potential of Chamaenerion angustifolium and Chamaenerion latifolium

The Chamaenerion genus, particularly Chamaenerion angustifolium and Chamaenerion latifolium, is recognized for its rich phytochemical composition and extensive medicinal properties. These species are abundant in polyphenols, flavonoids, and tannins, which contribute to their potent antioxidant, antimicrobial, and anticancer activities. This review provides a comprehensive analysis of their phytochemical constituents, with an emphasis on how processing methods, including fermentation, influence bioactivity. Notably, fermentation enhances the levels of key bioactive compounds, such as oenothein B, gallic acid, and ellagic acid, thereby increasing their pharmacological potential. Additionally, this review evaluates the biological activities of Chamaenerion species in relation to their chemical composition, while also considering the limitations of current studies, such as the lack of in vivo or clinical trials. The literature for this review was sourced from scientific databases, including PubMed, Scopus, and ScienceDirect, covering research from 2010 to 2024. Future studies should focus on optimizing extraction methods, elucidating synergistic bioactivities, and conducting in-depth clinical trials to validate their efficacy and safety.

Molecular Dynamics Simulation Studies of Beta-Glucogallin and Dihydro Dehydro Coniferyl Alcohol from Syzygium cumini for its Antimicrobial Activity on Staphylococcus aureus

With the escalating threat of antimicrobial resistance (AMR), discovering novel therapeutic agents against resistant pathogens like Staphylococcus aureus is crucial. This study explores phytochemicals from Syzygium cumini for their potential efficacy against AMR S. aureus infections, elucidating their mechanisms through in silico methods. We investigated 83 compounds from S. cumini, sourced from PubMed, using rigorous docking analysis against the ATP binding domain AgrC of S. aureus with AMdock with Autodock Vina v1.5.2. Drug-likeness predictions were assessed using SwissADME v2023 and Pass online v2.0. Molecular dynamics (MD) simulations identified promising compounds, focusing on stability and interaction dynamics. Beta-Glucogallin (BEG) and Dihydro Dehydro Coniferyl alcohol (DIH) emerged as significant hits. MD simulations with GROMACS v2020.6 revealed stable BEG and DIH complexes with AgrC, forming six hydrogen bonds with six key amino acids (Arg-303, Asp-338, Glu-342, Glu-384, Lys-389, Gly-396), indicating strong and stable bonding. The binding affinities for DIH and BEG are -73.474 ± 11.104 kJ/mol and -6.319 ± 18.823 kJ/mol with 4BXI, respectively. Our findings highlight BEG and DIH as promising candidates against AMR S. aureus infections, showing favourable binding affinities and stable interactions with AgrC. This study underscores the importance of natural products in combating AMR and demonstrates the utility of computational methodologies in drug discovery. Further experimental validation is warranted to fully exploit these phytochemicals' therapeutic potential.

A mechanistic overview on green assisted formulation of nanocomposites and their multifunctional role in biomedical applications

The importance of nanocomposites constantly attains attention because of their unique properties all across the fields especially in medical perspectives. The study of green-synthesized nanocomposites has grown to be extremely fascinating in the field of research. Nanocomposites are more promising than mono-metallic nanoparticles because they exhibit synergistic effects. This review encapsulates the current development in the formulation of plant-mediated nanocomposites by using several plant species and the impact of secondary metabolites on their biocompatible functioning. Phyto-synthesis produces diverse nanomaterials with biocompatibility, environment-friendliness, and in vivo actions, characterized by varying sizes, shapes, and biochemical nature. This process is advantageous to conventional physical and chemical procedures. New studies have been conducted to determine the biomedical efficacy of nanocomposites against various diseases. Unfortunately, there has been inadequate investigation into green-assisted nanocomposites. Incorporating phytosynthesized nanocomposites in therapeutic interventions not only enhances healing processes but also augments the host's immune defenses against infections. This review highlights the phytosynthesis of nanocomposites and their various biomedical applications, including antibacterial, antidiabetic, antiviral, antioxidant, antifungal, anti-cancer, and other applications, as well as their toxicity. This review also explores the mechanistic action of nanocomposites to achieve their designated tasks. Biogenic nanocomposites for multimodal imaging have the potential to exchange the conventional methods and materials in biomedical research. Well-designed nanocomposites have the potential to be utilized in various biomedical fields as innovative theranostic agents with the subsequent objective of efficiently diagnosing and treating a variety of human disorders.

Application of microfluidic technology and nanoencapsulation to amplify the antibacterial activity of clindamycin against a food born pathogen

Foodborne illnesses are often caused by microbial contamination during preparation or storage. In this work, stable nanoemulsions of clindamycin were prepared using Mentha piperita essential oil (MEO) as a nanocarrier delivery system. Response Surface Methodology was used to optimize the key variables for clindamycin nanoemulsion formulation, including 4.83, 2.83, and 0.14%w/w surfactant, essential oil, and clindamycin, respectively. The stability of MEO/clindamycin nanoemulsion (MEO/C NE) with a mean droplet size of 75.46 ± 3.2 nm was monitored over 3 months. The antibacterial activity of MEO/C NE and bulk compounds against E. coli bacterium was compared using a conventional method and a microfluidic chip. A significant difference in the antibacterial activity was observed by employing a microfluidic chip as compared to the conventional technique, probably due to a high contact surface area between the nanodroplets and bacterial membrane. In the microfluidic chip, the E. coli was completely inhibited in 30 min, whereas 3 h was needed for complete inhibition using the conventional method. The results of this study highlight the significance of nanoemulsion delivery systems to improve the antimicrobial activity of clindamycin and also microfluidic technology as a fast and reliable technique for examining antibiotics and nano delivery systems against microorganisms.

Antimicrobial efficacy of alternative root canal disinfection strategies: An evaluation on multiple working models

Researching disinfection strategies is pivotal because effectively eliminating bacteria and their byproducts during root canal treatment (RCT) remains a challenge. This study investigated the antimicrobial efficacy of natural antimicrobial compounds, propolis (PRO) and copaiba oil-resin (COR), compared to conventional agents in Endodontics. Antimicrobials were tested against endodontic pathogens via macrodilution with standardized inoculums to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). Biofilm killing efficacy were performed using two dual-species biofilms: Enterococcus faecalis (ATCC 29212) and Streptococcus mutans (ATCC 20523) and Streptococcus oralis (J22) and Actinomyces naeslundii (T14V-J1) grown on dentine discs. At the intratubular level (dentine cylinders), dentine tubule contamination was performed with E. faecalis and S. mutans. The specimens were exposed to antimicrobials to simulate their use at different sets of RCT and bacterial viability was quantified using Live/Dead staining via confocal laser scanning microscopy (CLSM). Biofilm characteristics and immediate removal of S. oralis and A. naeslundii biofilm model were evaluated employing optical coherence tomography (OCT) and CFU/mL counting. Statistical tests were applied according to data distribution for each analysis (α=0.05). Macrodilutions showed different effects against endodontic pathogens. Direct contact and intratubular analysis showed that PRO and COR promoted disinfection like conventional agents (p > 0.05). According to OCT analysis, PRO and COR showed similar biofilm reduction after immediate contact (p < 0.05). CFU/mL counting showed decontamination (p < 0.05) after using natural and conventional agents. PRO and COR showed antimicrobial effects, indicating their suitability as complementary approaches in RCT to eliminate as much microbial load as possible.

Release Profile and Antibacterial Activity of Thymus sibthorpii Essential Oil-Incorporated, Optimally Stabilized Type I Collagen Hydrogels

Antimicrobial resistance is one of the drastically increasing major global health threats due to the misuse and overuse of antibiotics as traditional antimicrobial agents, which render urgent the need for alternative and safer antimicrobial agents, such as essential oils (EOs). Although the strong antimicrobial activity of various EOs has already been studied and revealed, their characteristic high sensitivity and volatility drives the need towards a more efficient drug administration method via a biomaterial system. Herein, the potential of Thymus sibthorpii EO incorporated in functionalized antibacterial collagen hydrogels was investigated. At first, the optimally stabilized type I collagen hydrogels via six different multi-arm poly (ethylene glycol) succinimidyl glutarate (starPEG) crosslinkers were determined by assessing the free amine content and the resistance to enzymatic degradation. Subsequently, 0.5, 1, and 2% v/v of EO were incorporated into optimized collagen hydrogels, and the release profile, as well as release kinetics, were studied. Finally, biomaterial cytocompatibility tests were performed. Thymus sibthorpii EO was released from the hydrogel matrix via Fickian diffusion and showed sustained release and 0.5% v/v EO-loaded hydrogels showed adequate antibacterial activity against Staphylococcus aureus and did not show any statistically significant difference compared to penicillin (p < 0.05). Moreover, none of the fabricated composite antibacterial scaffolds displayed any cytotoxicity on NIH-3T3 fibroblasts. In conclusion, this work presents an innovative antibacterial biomaterial system for tissue engineering applications, which could serve as a promising alternative to antibiotics, contributing to coping with the issue of antimicrobial resistance.

Decoding nature: multi-target anti-inflammatory mechanisms of natural products in the TLR4/NF-κB pathway

Natural products are valuable medicinal resources in the field of anti-inflammation due to their significant bioactivity and low antibiotic resistance. Research has demonstrated that many natural products exert notable anti-inflammatory effects by modulating the Toll-like receptor 4 (TLR4) and nuclear factor kappa B (NF-κB) signaling pathways. The research on related signal transduction mechanisms and pharmacological mechanisms is increasingly being discovered and validated. However, there is currently a lack of comprehensive reviews focusing on the pharmacological mechanisms of natural products targeting the TLR4/NF-κB pathway for anti-inflammatory effects. In light of these considerations, this review comprehensively synthesizes recent research findings concerning the TLR4/NF-κB signaling pathway, including the translocation of TLR4 activation to lysosomes within the cytoplasm, the assembly of protein complexes mediated by ubiquitin chains K63 and K48, and the deacetylation modification of p65. These discoveries are integrated into the classical TLR4/NF-κB pathway to systematically elucidate the latest mechanisms among various targets. Additionally, we summarize the pharmacological mechanisms by which natural products exert anti-inflammatory effects through the TLR4/NF-κB pathway. This aims to elucidate the multitarget advantages of natural products in the treatment of inflammation and their potential applications, thereby providing theoretical support for molecular pharmacology research on inflammation and the development of novel natural anti-inflammatory drugs.

Exploring the antioxidant and antimicrobial properties of five indigenous Kenyan plants used in traditional medicine

Defined by the World Health Organization (WHO) as indigenous knowledge and practices used for maintaining health and treating illnesses, traditional medicine (TM) represents a rich reservoir of ancient healing practices rooted in cultural traditions and accumulated wisdom over centuries. Five indigenous Kenyan plant species traditionally used in African TM, named Afzelia quanzensis, Azadirachta indica, Gigasiphon macrosiphon, Grewia bicolor, and Lannea schweinfurthii, represent a valuable resource in healing practices, yet their chemical composition and bioactivity remain understudied. To depict a primary bio-chemical characterization of these plants, their antioxidant and antimicrobial features have been evaluated by the use of methods validated in this context. G. bicolor, and G. macrosiphon were found to have great potential as sources of bioactive metabolites, such as chlorophyll a (1456.29 µg/ g DW; 1104.33 µg/ g DW), chlorophyll b (712.48 µg/ g DW; 443.31 µg/ g DW), and carotenoids (369.71 µg/ g DW; 300 µg/ g DW) as well as phenols (31.78 mg GAE/g DW; 27.54 GAE/g DW), and exhibiting high antioxidant activity, according to TEAC, DPPH and FRAP assays. Additionally, L. schweinfurthii and G. macrosiphon demonstrated antimicrobial activity against the Gram-negative bacteria E. coli, as well as against Gram-positive ones, S. aureus and B. subtilis.

Chemical Composition and Antibacterial Effect of Clove and Thyme Essential Oils on Growth Inhibition and Biofilm Formation of Arcobacter spp. and Other Bacteria

Background: In recent years, significant resistance of microorganisms to antibiotics has been observed. A biofilm is a structure that significantly aids the survival of the microbial population and also significantly affects its resistance. Methods: Thyme and clove essential oils (EOs) were subjected to chemical analysis using gas chromatography coupled to mass spectrometry (GC-MS) and gas chromatography with a flame ionization detector (GC-FID). Furthermore, the antimicrobial effect of these EOs was tested in both the liquid and vapor phases using the volatilization method. The effect of the EOs on growth parameters was monitored using an RTS-8 bioreactor. However, the effect of the EOs on the biofilm formation of commonly occurring bacteria with pathogenic potential was also monitored, but for less described and yet clinically important strains of Arcobacter spp. Results: In total, 37 and 28 compounds were identified in the thyme and clove EO samples, respectively. The most common were terpenes and also derivatives of phenolic substances. Both EOs exhibited antimicrobial activity in the liquid and/or vapor phase against at least some strains. The determined antimicrobial activity of thyme and clove oil was in the range of 32-1024 µg/mL in the liquid phase and 512-1024 µg/mL in the vapor phase, respectively. The results of the antimicrobial effect are also supported by similar conclusions from monitoring growth curves using the RTS bioreactor. The effect of EOs on biofilm formation differed between strains. Biofilm formation of Pseudomonas aeruginosa was completely suppressed in an environment with a thyme EO concentration of 1024 µg/mL. On the other hand, increased biofilm formation was found, e.g., in an environment of low concentration (1-32 µg/mL). Conclusions: The potential of using natural matrices as antimicrobials or preservatives is evident. The effect of these EOs on biofilm formation, especially Arcobacter strains, is described for the first time.

Natural Inhibitors of Salmonella MDR Efflux Pumps AcrAB and AcrD: An Integrated In Silico, Molecular, and In Vitro Investigation

Multidrug-resistant (MDR) Salmonella remains a significant global health threat. This study aimed to explore the potential of essential oil components as novel inhibitors of the Salmonella MDR efflux pumps AcrAB and AcrD. Salmonella isolates were characterized for serotype, antibiotic resistance, and efflux pump activity. Essential oil components were screened for inhibitory effects using phenotypic and genotypic methods. In silico docking and molecular dynamics simulations were conducted to investigate binding interactions and stability. Salmonella Typhimurium was the predominant serotype with high MDR rates. Efflux pump activity was prevalent. Cumin and cinnamon oils demonstrated promising inhibitory effects on these pumps. Molecular docking simulations revealed strong binding affinities of analyzed compounds to the AcrAB and AcrD binding pocket. The 2-methyl-1-(p-tolyl)propan-2-ol exhibited higher stability within the AcrAB binding pocket compared to (1S,3R,5R)-1-isopropyl-4-methylenebicyclo[3.1.0]hexan-3-ol within the AcrD binding pocket. Treatment with these oils significantly downregulated efflux pump genes (robA, acrB, mdtB, acrF, acrD, soxS, mdsB, marA). The novel approach of combining in silico and molecular dynamics simulations with precise gene expression analysis provides a valuable framework for future studies aimed at combating MDR Salmonella efflux pumps.

Purification of Potential Antimicrobial Metabolites from Endophytic Fusarium oxysporum Isolated from Myrtus communis

The rise of microbial resistance and emerging infections pose significant health threats. Natural products from endophytic fungi offer a promising source of novel compounds with the potential as major drug leads. This research aims to screen Myrtus communis and Moringa oleifera for endophytic fungi and screen their metabolites for antibacterial and antifungal potential. Six endophytic fungal strains were isolated using a potato dextrose agar (PDA) medium. The M. communis isolates were designated MC1, MC2, and MC3, and the M. oleifera isolates were named MO1, MO2, and MO3. Preliminary bioactivity testing revealed that the MC3 isolate exhibited significant growth inhibition against multidrug-resistant bacterial and fungal pathogens, including Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Candida albicans, and Candida glabrata. The MC3 isolate was identified as Fusarium oxysporum through morphological and microscopic methods. For metabolite production, the fungal strain was cultured in potato dextrose broth (PDB) medium at 28 °C for 14 days in a shaking incubator. The metabolites were purified using various chromatographic techniques, HPLC and GC-MS. The GC-MS analysis of the bioactive compound containing fungal strain (F. oxysporum) revealed multiple compounds at different retention times using the NIST-20 Library. Based on RSI values and probability indices, two compounds were targeted for further purification. Structure elucidation was performed using 1D and 2D nuclear magnetic resonance (NMR) experiments on a Varian 500 NMR machine. The compounds identified were ethyl iso-allocholate (C26H44O5, exact mass 436.32) and 1-monolinoleoyl glycerol trimethylsilyl ether (C27H56O4Si2, exact mass 500.37). The MS (NIST-20) library facilitated the investigation of the in silico antimicrobial activity of these compounds against the elastase virulence protein of P. aeruginosa and protease Sapp1p from C. parapsilosis. Both the compounds were docked with druggable proteins using the Glide induced fit docking (IFD) algorithm. The ethyl iso-allocholate and 1-monolinoleoyl glycerol trimethylsilyl ether compounds showed binding scores - 10.07 kcal mol-1 and - 7.47 kcal mol-1 against elastase, and - 8.16 kcal mol-1 and - 6.89 kcal mol-1 against aspartic protease, respectively. In vitro studies confirmed the inhibitory activity of these compounds against multidrug-resistant P. aeruginosa and E. faecalis. Ethyl iso-allocholate exhibited higher bioactivity against P. aeruginosa with inhibition rates of 41%, 27%, and 35% at concentrations of 1000, 500, and 250 µg mL-1, respectively. These results suggest that bioactive compounds from F. oxysporum have the potential as antimicrobial agents, warranting further research.

Antibacterial Activity and Antifungal Activity of Monomeric Alkaloids

Scientists are becoming alarmed by the rise in drug-resistant bacterial and fungal strains, which makes it more costly, time-consuming, and difficult to create new antimicrobials from unique chemical entities. Chemicals with pharmacological qualities, such as antibacterial and antifungal elements, can be found in plants. Alkaloids are a class of chemical compounds found in nature that mostly consist of basic nitrogen atoms. Biomedical science relies heavily on alkaloid compounds. Based on 241 papers published in peer-reviewed scientific publications within the last ten years (2014-2024), we examined 248 natural or synthesized monomeric alkaloids that have antifungal and antibacterial activity against Gram-positive and Gram-negative microorganisms. Based on their chemical structure, the chosen alkaloids were divided into four groups: polyamine alkaloids, alkaloids with nitrogen in the side chain, alkaloids with nitrogen heterocycles, and pseudoalkaloids. With MIC values of less than 1 µg/mL, compounds 91, 124, 125, 136-138, 163, 164, 191, 193, 195, 205 and 206 shown strong antibacterial activity. However, with MIC values of below 1 µg/mL, compounds 124, 125, 163, 164, 207, and 224 demonstrated strong antifungal activity. Given the rise in antibiotic resistance, these alkaloids are highly significant in regard to their potential to create novel antimicrobial drugs.

Biochemistry and Future Perspectives of Antibiotic Resistance: An Eye on Active Natural Products

Antibiotic resistance poses a serious threat to the current healthcare system, negatively impacting the effectiveness of many antimicrobial treatments. The situation is exacerbated by the widespread overuse and abuse of available antibiotics, accelerating the evolution of resistance. Thus, there is an urgent need for novel approaches to therapy to overcome established resistance mechanisms. Plants produce molecules capable of inhibiting bacterial growth in various ways, offering promising paths for the development of alternative antibiotic medicine. This review emphasizes the necessity of research efforts on plant-derived chemicals in the hopes of finding and creating novel drugs that can successfully target resistant bacterial populations. Investigating these natural chemicals allows us to improve our knowledge of novel antimicrobial pathways and also expands our antibacterial repertoire with novel molecules. Simultaneously, it is still necessary to utilize present antibiotics sparingly; prudent prescribing practices must be encouraged to extend the effectiveness of current medications. The combination of innovative drug research and responsible drug usage offers an integrated strategy for managing the antibiotic resistance challenge.

Antimicrobial Impact of Wood Vinegar Produced Through Co-Pyrolysis of Eucalyptus Wood and Aromatic Herbs

BACKGROUND

The search for substances that can overcome microorganisms' resistance and enhance the antimicrobial activity of given products has attracted the attention of researchers. Eucalyptus wood vinegar (WV) is a promising product for developing alternative antimicrobials.

OBJECTIVES

This study aimed to evaluate whether the production of WV in the co-pyrolysis of eucalyptus wood with aromatic herbs would incorporate compounds from them into WV and if that would enhance its antimicrobial action.

METHODOLOGY

WV was produced alone and through co-pyrolysis with marjoram (Origanum majorana), Peruvian oregano (Origanum vulgare), rosemary (Salvia rosmarinus), thyme (Thymus vulgaris), and Turkish oregano (Origanum onites) at a proportion of 25% of herbs to the bone-dry wood weight. The antimicrobial effects were assessed against strains of gram-negative and -positive bacteria, and Candida glabrata. Microorganisms' colony growth in agar had their absorbances recorded after inoculation and incubation. Chemical characterization of the new products was performed by gas chromatography and mass spectrometry (GC/MS).

RESULTS

After coproduction, there were relevant chemical changes concerning the original WV. Thymol, for instance, was incorporated into the WV through co-pyrolysis with marjoram, Peruvian and Turkish oregano, and thyme. The coproducts were more efficient than the WV produced only with wood, with thyme-incorporated products having the highest efficiency. This can be attributed to the increase and incorporation of the substances after coproduction, and particularly the role of thymol in enhancing the antimicrobial action.

CONCLUSION

Given the results, the co-production of WV with eucalyptus wood and aromatic herbs has the potential to provide alternative antimicrobial products.

Natural compound-induced downregulation of antimicrobial resistance and biofilm-linked genes in wastewater Aeromonas species

Addressing the global antimicrobial resistance (AMR) crisis requires a multifaceted innovative approach to mitigate impacts on public health, healthcare and economic systems. In the complex evolution of AMR, biofilms and the acquisition of antimicrobial resistance genes (ARGs) play a pivotal role. Aeromonas is a major AMR player that often forms biofilm, harbors ARGs and is frequently detected in wastewater. Existing wastewater treatment plants (WWTPs) do not have the capacity to totally eliminate antimicrobial-resistant bacteria favoring the evolution of ARGs in wastewater. Besides facilitating the emergence of AMR, biofilms contribute significantly to biofouling process within the activated sludge of WWTP bioreactors. This paper presents the inhibition of biofilm formation, the expression of biofilm-linked genes and ARGs by phytochemicals andrographolide, docosanol, lanosterol, quercetin, rutin and thymohydroquinone. Aeromonas species were isolated and purified from activated sludge samples. The ARGs were detected in the isolated Aeromonas species through PCR. Aeromonas biofilms were quantified following the application of biocompounds through the microtiter plate assay. qPCR analyses of related genes were done for confirmation. Findings showed that the natural compounds inhibited the formation of biofilms and reduced the expression of genes linked to biofilm production as well as ARGs in wastewater Aeromonas. This indicates the efficacy of these compounds in targeting and controlling both ARGs and biofilm formation, highlighting their potential as innovative solutions for combating antimicrobial resistance and biofouling.

Antibacterial and antioxidant properties of sumac extract on methicillin-resistant Staphylococcus aureus

The research aimed to evaluate the antioxidative and antibacterial characteristics of aqueous sumac extract on methicillin-resistant Staphylococcus aureus through in-vitro and in-vivo study. Sumac extract has been obtained through the soaking method, and its antioxidant properties were gauged using the DPPH free radical scavenging method. The minimum inhibitory concentration (MIC) of sumac extract was determined on S. aureus obtained from hospitalized patients, as well as an assessment of biofilm-formation and the release of bacterial intracellular compounds. in vivo experimentation involved injecting bacteria (108 cfu/ml) into mice, which subsequently manifested indicators of symptoms of infection, and the number of bacteria within their bloodstream was quantified. The Sumac extract demonstrated strong antioxidant properties at concentrations of 1000 mg/ml. Furthermore, the agar tests for the gram staining, mannitol, coagulase, and DNase revealed that 190 cultured bacteria samples were identified as Staphylococcus aureus. These bacteria were resistant to clindamycin, ciprofloxacin, and methicillin antibiotics, but sensitive to erythromycin and penicillin antibiotics. Additionally, the bacteria displayed significant methicillin resistance and formed a strong biofilm (65.78%). The sumac extract showed a MIC range of 125-1000 µg/ml against Staphylococcus aureus. Treatment with concentrations above the MIC was found to prevent the formation of biofilm and increase the release of bacterial intracellular compounds. Sumac extract led to a decrease in bacterial count in the blood of mice and reduced signs of infection. Sumac extract demonstrated powerful antioxidant and antibacterial effects against resistant microorganisms, suggesting its potential as a promising compound for the treatment of resistant infections in future research.

In vitro and in silico studies of antibacterial activities of secofriedelane derivatives from Senna alata (L) Roxb

In this study, six compounds were obtained from a methanolic extract of air-dried leaves of Senna alata and one of them, a triterpenoid (secofriedelane) named as 7-(2-carboxyethyl)-3, 4b, 6a, 8, 10a, 12a-hexamethyl-8-vinyloctadecahydrochrysene-3-carboxylic acid (5) was isolated for the first time from this plant. Then, its chemical structure was detailed and characterised by FT-IR, 1H and 13C- NMR and ESI-MS. Besides, two chemical-modified derivatives of secofriedelane (5a, 5b) were synthesised by methylation and allylation reactions, respectively, and their in vitro antibacterial activities were also evaluated. The results revealed that all the triterpenes showed, against gram-positive and -negative bacterial strains, good and moderate antibacterial activities with bactericidal effects that were enhanced by the methyl groups and altered with the allyl ones. Moreover, the molecular docking results of 5, 5a and 5b in the DNA gyrase (2XCT) active site showed that triterpene 5 has a good score very close to reference (ciprofloxacin).

Antimicrobial and antibiofilm properties of procyanidins: potential for clinical and biotechnological applications

Procyanidins (PCs) have emerged as agents with potential antimicrobial and antibiofilm activities, although their mechanisms of action and structure-activity relationships remain poorly understood. This review assessed the potential mechanisms of action and applications of these compounds to explore these aspects. Studies on the antimicrobial properties of PCs suggest that they are involved in osmotic imbalance, DNA interactions and metabolic disruption. Although less studied, their antibiofilm activities include antiadhesive effects and the modulation of mobility and quorum sensing. However, most research has used uncharacterized plant extracts for in vitro assays, limiting the understanding of the structure-activity relationships of PCs and their in vivo mechanisms. Clinical trials on the antimicrobial and antibiofilm properties of PCs have not clarified these issues due to nonstandardized methodologies, inadequate chemical characterization, and the limited number of studies, preventing a consensus and evaluation of the in vivo effects. Additionally, patent analysis revealed that technological developments in the antimicrobial and antibiofilm uses of PCs are concentrated in health care and dental care, but new biotechnological uses are emerging. Therefore, while PCs are promising antimicrobial and antibiofilm compounds, further research into their chemical structures and mechanisms of action is crucial for evidence-based applications in biotechnology and health care.

Phytochemical and ethnomedicinal evidences of the use of Alternanthera brasiliana (L.) Kuntze against infectious diseases

ETHNOPHARMACOLOGICAL RELEVANCE

Popularly known as "penicilina" and "terramicina", Alternanthera brasiliana (L.) Kuntze belongs to the Amaranthaceae family and stands out for its ethnomedicinal uses in the treatment of infections caused by pathogenic microorganisms in some countries.

AIM OF THE STUDY

The present study aimed to carry out a literature review and analyze whether the scientific evidence really validates the numerous indications for the use of A. brasiliana in traditional medicine for the treatment of infectious diseases. Phytochemical and toxicological studies related to this species were also analyzed.

MATERIAL AND METHODS

Scientific documents were retrieved from Google Scholar, PubMed®, ScienceDirect®, SciELO, SpringerLink®, Scopus®, and Web of Science™ databases. The literature was reviewed from the first report on the antimicrobial activity of A. brasiliana in 1994 until April 2024.

RESULTS

According to the scientific documents analyzed, it was observed that A. brasiliana is widely used as a natural antibiotic for the treatment of infectious diseases in Brazil, mainly in the states of Rio Grande do Sul, Mato Grosso, and Minas Gerais. Its ethnomedicinal uses have also been reported in other countries such as Colombia and India. The leaves (78%) of A. brasiliana are the main parts used in the preparation of herbal medicines by traditional communities. Several A. brasiliana extracts showed low activity when evaluated against pathogens, including gram-positive bacteria, gram-negative bacteria, parasitic protozoa, and fungi. Only two studies reported that extracts from this plant showed high activity against the herpes simplex virus, Mycobacterium smegmatis, and Candida albicans. Phytochemicals belonging to the classes of phenolic compounds and flavonoid (52%), saturated and unsaturated fatty acids (33%), steroids and phytosterols (8%), terpenoids (5%), and fatty alcohol esters (2%) were identified in A. brasiliana. Toxicity (in vivo) and cytotoxicity (in vitro) studies of polar and non-polar extracts obtained from A. brasiliana leaves indicated that this plant is biologically safe.

CONCLUSION

Despite being widely used as a natural antibiotic by traditional communities, scientific investigations related to the antimicrobial potential of A. brasiliana extracts have indicated inactivity against several pathogens.

Lessons learnt from broad-spectrum coronavirus antiviral drug discovery

INTRODUCTION

Highly pathogenic coronaviruses (CoVs), such as severe acute respiratory syndrome CoV (SARS-CoV), Middle East respiratory syndrome CoV (MERS-CoV), and the most recent SARS-CoV-2 responsible for the COVID-19 pandemic, pose significant threats to human populations over the past two decades. These CoVs have caused a broad spectrum of clinical manifestations ranging from asymptomatic to severe distress syndromes (ARDS), resulting in high morbidity and mortality.

AREAS COVERED

The accelerated advancements in antiviral drug discovery, spurred by the COVID-19 pandemic, have shed new light on the imperative to develop treatments effective against a broad spectrum of CoVs. This perspective discusses strategies and lessons learnt in targeting viral non-structural proteins, structural proteins, drug repurposing, and combinational approaches for the development of antivirals against CoVs.

EXPERT OPINION

Drawing lessons from the pandemic, it becomes evident that the absence of efficient broad-spectrum antiviral drugs increases the vulnerability of public health systems to the potential onslaught by highly pathogenic CoVs. The rapid and sustained spread of novel CoVs can have devastating consequences without effective and specifically targeted treatments. Prioritizing the effective development of broad-spectrum antivirals is imperative for bolstering the resilience of public health systems and mitigating the potential impact of future highly pathogenic CoVs.

Ovomucin and its hydrolysates differentially influenced colitis severity in Citrobacter rodentium-infected mice

Egg white protein ovomucin and its hydrolysates were previously reported to exhibit anti-inflammatory and anti-adhesive activities. However, their potential to regulate pathogen colonization and disease severity has not been fully characterized. To investigate the effects of ovomucin (OVM) and its hydrolysates including ovomucin-Protex 26L (OP) and -pepsin/pancreatin (OPP) on host resistance to pathogen infection, a well-documented colitis model in mice for attaching and effacing E. coli pathogens, Citrobacter rodentium, was used in the current study. C57Bl/6J female mice were fed on a basal diet supplemented with OVM or its hydrolysates for 3 weeks prior to the C. rodentium challenge, with the dietary treatments continued for seven days. Body weight was not affected throughout the experimental period. OP supplementation resulted in lower (P < 0.05) pathogen loads at 7 dpi. Attenuated colitis severity was observed in mice that received OVM and OP, as indicated by reduced colonic pathological scores and pro-inflammatory responses compared with the infected control group. In contrast, OPP consumption resulted in enhanced C. rodentium colonization and disease severity. Notably, reduced microbial diversity indices of the gut microbiota were observed in the OPP-supplemented mice compared with the OVM- and OP-supplemented groups. This study showed the potential of OVM and OP to alleviate the severity of colitis induced by infection while also suggesting the opposite outcome of OPP in mitigating enteric infection.

Meta-analysis of antimicrobial activity of Allium, Ocimum, and Thymus spp. confirms their promising application for increasing food safety

Biopreservation strategies such as the use of Mediterranean plant extracts to ensure food safety are promising to deal with the emergence of antimicrobial resistances and the overreliance on food chemical additives. In the last few decades, antimicrobial susceptibility testing (AST) for evaluating the in vitro antibacterial potential of plant extracts against the most relevant foodborne pathogens has been widely reported in the literature. The current meta-analysis aimed to summarise and analyse the extensive evidence available in the literature regarding the in vitro antimicrobial capability of Allium, Ocimum and Thymus spp. extracts against foodborne pathogens. A systematic review was carried out to gather data on AST results of these extracts against Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., Escherichia coli and Bacillus cereus, including inhibition diameters (ID) and minimum inhibitory concentrations (MIC). A total of 742 records were gathered from a raw collection of 2,065 articles. Weighted mixed-effect linear models were adjusted to data to obtain pooled ID, pooled MIC and the relationship between both model estimations and observations. The pooled results revealed B. cereus as the most susceptible bacteria to Allium sativum (pooled ID = 20.64 ± 0.61 mm) by diffusion methods and S. aureus (pooled MIC = 0.146 mg/mL) by dilution methods. Diffusion methods did not yield conclusive results for Ocimum spp. extracts; however, the lowest pooled MIC was obtained for S. aureus (0.263 mg/mL). Among the foodborne pathogens evaluated, B. cereus showed the highest sensitivity to Thymus spp. extracts by both diffusion and dilution methods (pooled ID = 28.90 ± 2.34 mm and MIC = 0.075 mg/mL). The methodology used for plant extraction was found to not significantly affect MIC values (p > 0.05). Overall, the antimicrobial effectiveness of the studied extracts against Gram-positive and Gram-negative bacteria was demonstrated. Finally, the robustness of the meta-regression model was confirmed, also revealing an inversely proportional correlation between the ID and MIC measurements (p < 0.0001). These results provide a robust scientific basis on the factors affecting the in vitro antimicrobial efficacy of extracts from Mediterranean plants. They also provide valuable information for stakeholders involved in their industrial application in food, including producers, regulatory agencies and consumers which demand green-labelled foods.

Bioactivity of Eugenol: A Potential Antibiotic Adjuvant with Minimal Ecotoxicological Impact

Combining commercial antibiotics with adjuvants to lower their minimum inhibitory concentration (MIC) is vital in combating antimicrobial resistance. Evaluating the ecotoxicity of such compounds is crucial due to environmental and health risks. Here, eugenol was assessed as an adjuvant for 7 commercial antibiotics against 14 pathogenic bacteria in vitro, also examining its acute ecotoxicity on various soil and water organisms (microbiota, Vibrio fischeri, Daphnia magna, Eisenia foetida, and Allium cepa). Using microdilution methods, checkerboard assays, and kinetic studies, the MICs for eugenol were determined together with the nature of its combinations with antibiotics against bacteria, some unexposed to eugenol previously. The lethal dose for the non-target organisms was also determined, as well as the Average Well Color Development and the Community-Level Physiological Profiling for soil and water microbiota. Our findings indicate that eugenol significantly reduces MICs by 75 to 98%, which means that it could be a potent adjuvant. Ecotoxicological assessments showed eugenol to be less harmful to water and soil microbiota compared to studied antibiotics. While Vibrio fischeri and Daphnia magna were susceptible, Allium cepa and Eisenia foetida were minimally affected. Given that only 0.1% of eugenol is excreted by humans without metabolism, its environmental risk when used with antibiotics appears minimal.

The Antimicrobial Effect of Cornus mas L. and Sorbus aucuparia L. Fruit Extracts against Resistant Uropathogens in Correlation with the Prevalence of Urinary Tract Infections in Companion Animals

Urinary tract infections (UTIs) are a widespread condition in pets, with many antibiotics being prescribed, contributing to the rise in antimicrobial resistance, which is a worldwide threat. This study's main objective was to analyze the in vitro antimicrobial activity of Cornus mas and Sorbus aucuparia fruit hydro-ethanolic extracts towards bacteria identified in the urine of companion animals experiencing UTIs. Urine samples were collected from dogs and cats (n = 83; 47 negative, 36 positive); several bacterial strains were identified (n = 49) belonging to the Escherichia, Enterococcus, Staphylococcus, Proteus, Klebsiella, Enterobacter, Pseudomonas, Acinetobacter, Leclercia, and Kocuria genera. Bacterial susceptibility was tested using the disk diffusion method, with the majority being resistant to several beta-lactams, quinolones, trimethoprim/sulfamethoxazole, and nitrofurantoin. Subsequently, 13 resistant isolates were selected to evaluate the fruits extracts' antimicrobial potential using the agar well diffusion and broth microdilution methods. Cornus mas exhibited the greatest activity against Gram-negatives (primarily Pseudomonas luteola), while Sorbus aucuparia showed maximum effects towards Gram-positives (particularly Enterococcus faecalis). The MIC was 0.01 μg/μL for both extracts; the MBC was 0.08 μg/μL for Cornus mas and 0.05 μg/μL for Sorbus aucuparia. However, Cornus mas showed a stronger bactericidal effect. This is the first study to investigate these fruit extracts in UTI isolates of companion animals, and these extracts might be used as substitutes or adjuvants for antibiotics, thus contributing to a reduction in antimicrobial resistance.

Remarkable enhancement of cinnamaldehyde antimicrobial activity encapsulated in capped mesoporous nanoparticles: A new "nanokiller" approach in the era of antimicrobial resistance

Combating antimicrobial resistance is one of the biggest health challenges because of the ineffectiveness of standard biocide treatments. This challenge could be approached using natural products, which have demonstrated powerful therapeutics against multidrug-resistant microbes. In the present work, a nanodevice consisting of mesoporous silica nanoparticles loaded with an essential oil component (cinnamaldehyde) and functionalized with the polypeptide ε-poly-l-lysine is developed and used as an antimicrobial agent. In the presence of the corresponding stimuli (i.e., exogenous proteolytic enzymes from bacteria or fungi), the polypeptide is hydrolyzed, and the cinnamaldehyde delivery is enhanced. The nanodevice's release mechanism and efficacy are evaluated in vitro against the pathogenic microorganisms Escherichia coli, Staphylococcus aureus, and Candida albicans. The results demonstrate that the new device increases the delivery of the cinnamaldehyde via a biocontrolled uncapping mechanism triggered by proteolytic enzymes. Moreover, the nanodevice notably improves the antimicrobial efficacy of cinnamaldehyde when compared to the free compound, ca. 52-fold for E. coli, ca. 60-fold for S. aureus, and ca. 7-fold for C. albicans. The enhancement of the antimicrobial activity of the essential oil component is attributed to the decrease of its volatility due to its encapsulation in the porous silica matrix and the increase of its local concentration when released due to the presence of microorganisms.

Effect of allyl-isothiocyanate on survival and antimicrobial peptide expression following oral bacterial infections in Drosophila melanogaster

Since infections with antibiotic-resistant bacteria cause increasing problems worldwide, the identification of alternative therapies is of great importance. Plant-derived bioactives, including allyl-isothiocyanate (AITC), have received attention for their antimicrobial properties. The present study therefore investigates the impact of AITC on survival and antimicrobial peptide (AMP) levels in Drosophila melanogaster challenged with the fly pathogenic bacteria Pectobacterium carotovorum subsp. carotovorum and Leuconostoc pseudomesenteroides. AITC, a sulfur-containing compound derived from glucosinolates, exhibits antimicrobial properties and has been suggested to modulate AMP expression. By using D. melanogaster, we demonstrate that AITC treatment resulted in a concentration-dependent decrease of survival rates among female flies, particularly in the presence of the Gram-negative bacterium Pectobacterium carotovorum subsp. carotovorum, whereas AITC did not affect survival in male flies. Despite the ability of isothiocyanates to induce AMP expression in cell culture, we did not detect significant changes in AMP mRNA levels in infected flies exposed to AITC. Our findings suggest sex-specific differences in response to AITC treatment and bacterial infections, underlining the complexity of host-pathogen interactions and potential limitations of AITC as a preventive or therapeutic compound at least in D. melanogaster models of bacterial infections.

A comprehensive study on Geranium robertianum L. antibacterial potential

AIMS

The research aimed to optimize the ultrasound-assisted extraction of secondary metabolites and the antibacterial activity of the plant species Geranium robertianum. The phytochemical profiles of the optimized extracts, as well as their antibacterial and synergistic activity with an antibiotic and their potential mechanisms of action and cytotoxicity, were examined.

METHODS AND RESULTS

Response Surface Methodology was used to optimize extraction conditions. Optimized ethanol and acetone extracts were tested via microdilution, checkerboard, time-kill kinetics, and cell membrane permeability methods. The extracts displayed broad antibacterial activity with minimum inhibitory concentrations ranging from 1.25 to 20 mg ml-1. In addition, the extract synergistically reacted with gentamicin against gentamicin-resistant strains of Escherichia coli and Staphylococcus aureus, enhancing the efficacy of the antibiotic up to 32-fold. The extracts demonstrated strain-dependent bactericidal activity in a 24-h time interval. They increase the permeability of the cell membrane, thus disrupting its normal functioning. The cytotoxic concentration (CC50) on human keratinocytes was 1771.24 ± 5.78 µg ml-1 for ethanol extract, and 958.01 ± 6.14 µg ml-1 for acetone extract. Kaempferol, ellagic acid, quercetin, and rutin were recognized as the main components in both extracts.

CONCLUSIONS

The findings of this study indicate that the extracts of G. robertianum can be considered as potential natural antibacterial agents in the control of microorganisms.

Antimicrobial and antibiofilm activity of specialized metabolites isolated from Centaurea hyalolepis

The discovery of plant-derived compounds that are able to combat antibiotic-resistant pathogens is an urgent demand. Over years, Centaurea hyalolepis attracted considerable attention because of its beneficial medical properties. Phytochemical analyses revealed that Centaurea plant species contain several metabolites, such as sesquiterpene lactones (STLs), essential oils, flavonoids, alkaloids, and lignans.The organic extract of C. hyalolepis plant, collected in Palestine, showed significant antimicrobial properties towards a panel of Gram-negative and Gram-positive bacterial strains when the Minimal Inhibitory Concentration (MIC) values were evaluated by broth microdilution assays. A bio-guided fractionation of the active extract via multiple steps of column and thin layer chromatography allowed us to obtain three main compounds. The isolated metabolites were identified as the STLs cnicin, 11β,13-dihydrosalonitenolide and salonitenolide by spectroscopic and spectrometric analyses. Cnicin conferred the strongest antimicrobial activity among the identified compounds. Moreover, the evaluation of its antibiofilm activity by biomass assays through crystal violet staining revealed almost 30% inhibition of biofilm formation in the case of A. baumannii ATCC 17878 strain. Furthermore, the quantification of carbohydrates and proteins present in the extracellular polymeric substance (EPS) revealed the ability of cnicin to significantly perturb biofilm structure. Based on these promising results, further investigations might open interesting perspectives to its applicability in biomedical field to counteract multidrug resistant infections.

Biodiversity and Bioactive Potential of Actinomycetes from Unexplored High Altitude Regions of Kargil, India

The effectiveness of currently available antimicrobials and anticancer medications is steadily declining due to the emergence of drug resistance. Since actinobacteria are important producers of bioactive substances, we have isolated them from the soil samples of exotic North-Western Himalayan terrains. Out of 128 isolates, 39 strains were prioritized based on their bioactive potential. The diversity analysis revealed higher abundance distribution of actinomycetes in the soil of an open field (68.7%), followed by the mountainside (34.9%), from which most of the bioactive strains were obtained. The extract of the strain S26-11 was found to be highly active against Gram-positive Staphylococcus aureus and Bacillus subtilis with a MIC of 0.5 μg/mL and 1 μg/mL respectively. A cytotoxicity assay (sulforhodamine B) was performed on a series of cancer cell lines (PC-3, MCF-7, A-549, and HCT-116). The extract of the strain S26-11 showed cytotoxic activity against all cancer cell lines with an IC50 of 2 µg/mL against PC-3, 1.9 µg/mL against MCF-7, 0.52 µg/mL against A-549, and 0.83 µg/mL against HCT-116. Moreover, the antioxidant activity was assessed using a DPPH-based assay and the results revealed that the S17-8 isolate showed the highest antioxidant activity with IC50 of 114.136 μg/mL. The Response Surface Methodology (RSM) had helped to optimize the physical parameters for scaling up of the bioactive strain S26-11. The unexplored soil niches of Kargil (UT, Ladakh), India, is rich in actinomycetes which are having potential bioactivities, would be worth to explore for the discovery of bioactive compounds.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-023-01133-1.

Antimicrobial Potency of Fmoc-Phe-Phe Dipeptide Hydrogels with Encapsulated Porphyrin Chromophores Is a Promising Alternative in Antimicrobial Resistance

Antimicrobial resistance (AMR) poses a significant global health risk as a consequence of misuse of antibiotics. Owing to the increasing antimicrobial resistance, it became imperative to develop novel molecules and materials with antimicrobial properties. Porphyrins and metalloporphyrins are compounds which present antimicrobial properties especially after irradiation. As a consequence, porphyrinoids have recently been utilized as antimicrobial agents in antimicrobial photodynamic inactivation in bacteria and other microorganisms. Herein, we report the encapsulation of porphyrins into peptide hydrogels which serve as delivery vehicles. We selected the self-assembling Fmoc-Phe-Phe dipeptide, a potent gelator, as a scaffold due to its previously reported biocompatibility and three different water-soluble porphyrins as photosensitizers. We evaluated the structural, mechanical and in vitro degradation properties of these hydrogels, their interaction with NIH3T3 mouse skin fibroblasts, and we assessed their antimicrobial efficacy against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria. We found out that the hydrogels are cytocompatible and display antimicrobial efficiency against both strains with the zinc porphyrins being more efficient. Therefore, these hydrogels present a promising alternative for combating bacterial infections in the face of growing AMR concerns.

Molecular insight into thymoquinone mechanism of action against Mycobacterium tuberculosis

Natural products are promising antimicrobials, usually having multiple and different cellular targets than synthetic antibiotics. Their influence on bacteria at various metabolic and functional levels contributes to higher efficacy even against drug-resistant strains. One such compound is a naturally occurring p-benzoquinone - thymoquinone. It is effective against different bacteria, including multidrug-resistant and extremely drug-resistant Mycobacterium tuberculosis. Its antibacterial mechanism of action was studied in several bacterial species except mycobacteria. To get an insight into the antimycobacterial activity of thymoquinone at the molecular level, we performed metabolomic and transcriptomic analyzes of bacteria exposed to this compound. The expression of genes coding stress-responsive sigma factors revealed that thymoquinone rapidly induces the production of sigE transcripts. At the same time, prolonged influence results in the overexpression of all sigma factor genes and significantly upregulates sigF. The metabolomic analysis confirmed that the antimycobacterial activity of thymoquinone was related to the depletion of NAD and ATP pools and the downregulation of plasma membrane lipids. This state was observed after 24 h and was persistent the next day, suggesting that bacteria could not activate catabolic mechanisms and produce energy. Additionally, the presence of a thymoquinone nitrogen derivative in the bacterial broth and the culture was reported.

In vitro study: methylene blue-based antibacterial photodynamic inactivation of Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most antibiotic-resistant and opportunistic pathogens in immunocompromised and debilitated patients. It is considered the cause of most severe skin infections and is frequently found in hospital burn units. Due to its high antibiotic resistance, eliminating P. aeruginosa from skin infections is quite challenging. Therefore, this study aims to assess the novel in vitro antibacterial activity of methylene blue using a 635-nm diode laser to determine the effective power and energy densities for inhibition of P. aeruginosa. The strain was treated with various concentrations of methylene blue and 635-nm diode laser at powers of 300 mW/cm2 and 250 mW/cm2. The diode laser's potency in the photo-destruction of methylene blue and its degradation through P. aeruginosa were also evaluated. Colony-forming unit (CFU)/ml, fluorescence spectroscopy, optical density, and confocal microscopy were used to measure the bacterial killing effect. As a result, the significant decrease of P. aeruginosa was 2.15-log10, 2.71-log10, and 3.48-log10 at 60, 75, and 90 J/cm2 after excitation of MB for 240, 300, and 360 s at a power of 250 mW/cm2, respectively. However, a maximum decrease in CFU was observed by 2.54-log10 at 72 J/cm2 and 4.32-log10 at 90 and 108 J/cm2 after 300 mW/cm2 of irradiation. Fluorescence images confirmed the elimination of bacteria and showed a high degree of photo-destruction compared to treatment with methylene blue and light alone. In conclusion, MB-induced aPDT demonstrated high efficacy, which could be a potential approach against drug-resistant pathogenic bacteria. KEY POINTS: • Combination of methylene blue with 635-nm diode laser for antibacterial activity. • Methylene blue photosensitizer is employed as an alternative to antibiotics. • aPDT showed promising antibacterial activity against Pseudomonas aeruginosa.

Effect of palladium(II) complexes on NorA efflux pump inhibition and resensitization of fluoroquinolone-resistant Staphylococcus aureus: in vitro and in silico approach

Staphylococcus aureus leads to diverse infections, and their treatment relies on the use of antibiotics. Nevertheless, the rise of antibiotic resistance poses an escalating challenge and various mechanisms contribute to antibiotic resistance, including modifications to drug targets, enzymatic deactivation of drugs, and increased efflux of antibiotics. Hence, the quest for innovative antimicrobial solutions has intensified in the face of escalating antibiotic resistance and the looming threat of superbugs. The NorA protein of S. aureus, classified as an efflux pump within the major facilitator superfamily, when overexpressed, extrudes various substances, including fluoroquinolones (such as ciprofloxacin) and quaternary ammonium. Addressing this, the unexplored realm of inorganic and organometallic compounds in medicinal chemistry holds promise. Notably, the study focused on investigating two different series of palladium-based metal complexes consisting of QSL_PA and QSL_PB ligands to identify a potent NorA efflux pump inhibitor that can restore the susceptibility to fluoroquinolone antibiotics. QSL_Pd5A was identified as a potent efflux pump inhibitor from the real-time efflux assay. QSL_Pd5A also resensitized SA1199B to ciprofloxacin at a low concentration of 0.125 µg/mL without elucidating cytotoxicity on the NRK-62E cell line. The in vitro findings were substantiated by docking results, indicating favorable interactions between QSL_Pd5A and the NorA efflux pump.

Synthesis of Seven Indolizine-Derived Pentathiepines: Strong Electronic Structure Response to Nitro Substitution in Position C-9

Seven new 1,2,3,4,5-pentathiepino[6,7-a]indolizines were synthesized in which the pentathiepine moieties bear an indolizine backbone that is derivatized from C-H to F-, Cl-, Br-, I-, NO2-, and CH3-substitutions, respectively, in a meta position relative to the aza group on the pyridine moiety. Their preparation took place via two common steps: (i) a Sonogashira coupling between (4-substituted) 2-bromo- or 2-chloropyridines and propynyl 3,3-diethylacetal, and (ii) a ring closing reaction mediated by a molybdenum oxo-bistetrasulfido complex and elemental sulfur. The latter simultaneously facilitates the 1,2,3,4,5-pentathiepino chain/ring- and indolizine ring-formations. The fluoro derivative was addressed with 2-bromo-5-aminopyridine as the starting material via a Sandmeyer reaction. The iodo derivative was obtained from 5-bromo-2-alkynylpiridine using a metal-assisted variation of the Finkelstein reaction. The requirement to explore different reaction conditions and the varied respective yields of the final products are discussed. The influence of the distinct substitutions on the pyridine moieties, their electronic structures, and respective chemical properties was investigated through a set of spectroscopic/analytical characterizations. Intriguingly, in all cases, the nitro-substituted derivative exhibited a distinct behavior compared to the six other investigated derivatives, which was also addressed computationally. All seven new pentathiepines were crystallized, and their respective molecular structures were determined using single crystal X-ray diffraction. These structures are compared and discussed as are their respective packing patterns.

Verbascoside-Rich Plant Extracts in Animal Nutrition

In recent years, the search for dietary intervention with natural products able to sustain animal health and decrease environmental impact, has raised the number of studies pertaining to the use of plants' secondary metabolites. In fact, in livestock, there is a clear relationship between the animals' antioxidant status and the onset of some diseases that negatively affect animal welfare, health, and productive performance. An interesting compound that belongs to the secondary metabolites family of plants, named phenylpropanoids, is verbascoside. The genus Verbascum, which includes more than 233 plant species, is the genus in which this compound was first identified, but it has also been found in other plant extracts. Verbascoside exhibits several properties such as antioxidant, anti-inflammatory, chemopreventive, and neuroprotective properties, that have been evaluated mainly in in vitro studies for human health. The present work reviews the literature on the dietary integration of plant extracts containing verbascoside in livestock. The effects of dietary plant extracts containing verbascoside on the productive performance, antioxidant status, blood parameters, and meat quality in several animal species were evaluated. The present data point out that dietary plant extracts containing verbascoside appear to be a favorable dietary intervention to enhance health, antioxidant status, and product quality in livestock.

Nutraceutical Potential of Lentinula edodes' Spent Mushroom Substrate: A Comprehensive Study on Phenolic Composition, Antioxidant Activity, and Antibacterial Effects

Lentinula edodes, commonly known as shiitake mushroom, is renowned for its potential health advantages. This research delves into the often-overlooked by-product of shiitake cultivation, namely spent mushroom substrate (SMS), to explore its nutraceutical properties. The SMS samples were collected and subjected to different extraction methods, namely short or long agitation, and ultrasound-assisted extractions using different temperatures and distilled water or a 50% (v/v) ethanol as solvents. The extracts were tested for phenolic content (total phenols, ortho-diphenols, and flavonoids), antioxidant capacity (DPPH, 2,2-diphenyl-1 picrylhydrazyl; ABTS, 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid; and FRAP, ferric reducing antioxidant power), and antibacterial activity. The different extraction methods revealed substantial variations (p < 0.05) in phenolic composition and antioxidant capacity. The highest phenolic content and antioxidant capacity were achieved using 24 h extraction, agitation, 50 °C, and ethanol as the solvent. Furthermore, the extracted compounds displayed antibacterial activity in specific tested bacterial strains. This study highlights the nutraceutical potential of L. edodes' SMS, positioning it as a valuable dietary supplement for animal nutrition, with emphasis on its prebiotic properties. Hence, this research unveils the promising health benefits of SMS in both human and animal nutrition.

Whole-transcriptome analysis reveals mechanisms underlying antibacterial activity and biofilm inhibition by a malic acid combination (MAC) in Pseudomonas aeruginosa

Background

Pseudomonas aeruginosa is a highly prevalent bacterial species known for its ability to cause various infections and its remarkable adaptability and biofilm-forming capabilities. In earlier work, we conducted research involving the screening of 33 metabolites obtained from a commercial source against two prevalent bacterial strains, Escherichia coli and Staphylococcus aureus. Through screening assays, we discovered a novel malic acid combination (MAC) consisting of malic acid, citric acid, glycine, and hippuric acid, which displayed significant inhibitory effects. However, the precise underlying mechanism and the potential impact of the MAC on bacterial biofilm formation remain unknown and warrant further investigation.

Methods

To determine the antibacterial effectiveness of the MAC against Pseudomonas aeruginosa, we conducted minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques were employed to observe bacterial morphology and biofilm formation. We further performed a biofilm inhibition assay to assess the effect of the MAC on biofilm formation. Whole-transcriptome sequencing and bioinformatics analysis were employed to elucidate the antibacterial mechanism of the MAC. Additionally, the expression levels of differentially expressed genes were validated using the real-time PCR approach.

Results

Our findings demonstrated the antibacterial activity of the MAC against P. aeruginosa. SEM analysis revealed that the MAC can induce morphological changes in bacterial cells. The biofilm assay showed that the MAC could reduce biofilm formation. Whole-transcriptome analysis revealed 1093 differentially expressed genes consisting of 659 upregulated genes and 434 downregulated genes, in response to the MAC treatment. Mechanistically, the MAC inhibited P. aeruginosa growth by targeting metabolic processes, secretion system, signal transduction, and cell membrane functions, thereby potentially compromising the survival of this human pathogen. This study provides valuable insights into the antibacterial and antibiofilm activities of the MAC, a synergistic and cost-effective malic acid combination, which holds promise as a potential therapeutic drug cocktail for treating human infectious diseases in the future.

Synergistic antibacterial effects of exopolysaccharides/nickel-nanoparticles composites against multidrug-resistant bacteria

The need for an alternative treatment to fight infectious diseases caused by antibiotic-resistant bacteria is increasing. A possible way to overcome bacterial resistance to antibiotics is by reintroducing commonly used antibiotics with a sensitizer capable of enhancing their antimicrobial effect in resistant bacteria. Here, we use a composite composed of exopolysaccharide capped-NiO NPs, with antimicrobial effects against antibiotic-resistant Gram-positive and Gram-negative bacteria. It potentiated the antimicrobial effects of four different antibiotics (ampicillin, kanamycin, chloramphenicol, and ciprofloxacin) at lower concentrations than their minimal inhibitory concentrations. We observed that the Ni-composite synergistically enhanced, fourfold, the antibacterial effect of kanamycin and chloramphenicol against multidrug-resistant Staphylococcus aureus and Pseudomonas aeruginosa, as well as ampicillin against multidrug-resistant Staphylococcus aureus, and ciprofloxacin against multidrug-resistant Pseudomonas aeruginosa by eightfold. We also found that Ni-composite could not inhibit biofilm synthesis on the tested bacterial strains. Our results demonstrated the possibility of using metal nanoparticles, like NiO, as a sensitizer to overcome bacterial antibiotic resistance.

Bacillus subtilis RBT-7/32 and Bacillus licheniformis RBT-11/17 as New Promising Strains for Use in Probiotic Feed Additives

The normal functioning of a gastrointestinal microflora in poultry and livestock is of significant importance, since its imbalance negatively influences an organism's functions. In this study, the UV mutagenesis and selection were used to obtain two Bacillus strains possessing antagonistic activity towards Escherichia coli and Staphylococcus aureus, and their potential as a probiotic feed additive was evaluated. Compared to the parental strains, the ability of B. subtilis RBT-7/32 and B. licheniformis RBT-11/17 strains to suppress E. coli increased by 77 and 63%, respectively; the corresponding ability of these strains to suppress S. aureus increased by 80 and 79%, respectively. RBT-11/17 could not utilize microcrystalline cellulose and carboxymethyl cellulose, whereas cellulolytic activity of RBT-7/32 was doubled compared to the initial strain. The amylolytic activity of new strains was increased by 40%. Cultivation of strains on media containing soybean, pea, and corn meal did not provide any difference in the biomass production compared to the control. The heating of a water suspension of a dried biomass of the strains for 10-20 min at 80 and 100 °C or incubation in water solutions of citric, ascorbic, acetic, and formic acids (pH 3.0) for 3 and 24 h at 40 °C did not provide any negative influence on the spore survivability. Both strains were evaluated for their resistance to a number of veterinary antibiotics. Thus, RBT-7/32 and RBT-11/17 strains have good prospects for use in feed additives.

Antibacterial and phytochemical analysis of traditional medicinal plants: An alternative therapeutic Approach to conventional antibiotics

The purpose of this study was to carry out antibacterial and phytochemical analyses on six selected medicinal plants that have been traditionally used by the local people to treat and control different diseases. The antibacterial activities of methanolic extracts of these plants were assessed using the Agar well diffusion and Microtiter broth dilution methods. The root extract of Andrachne aspera showed significantly (p < 0.05) highest mean zone of inhibition at concentrations of 100 mg/ml (33 ± 0.17) and 200 mg/ml (33.5 ± 0.84) against S. epidermidis. The second highest mean zone of inhibition (24.8 ± 0.41) was recorded by Dichrostachys cinerea leaf extract against S. epidermidis at 200 mg/ml concentration. The minimum inhibitory concentrations 1.0 ± 0.0 was recorded by Andrachne aspera against E. faecalis and 2.0 ± 0.0 against S. aureus by Dichrostachys cinerea. The preliminary phytochemical analysis showed that Andrachne aspera and Dichrostachys cinerea contained strong concentration of Polyphenols and Flavonoids. Therefore, these two medicinal plant species have promising potential for further detailed investigations, including safety tests, characterization and isolation of bioactive secondary metabolites for the development of alternative drugs.

An update on the potential mechanism of gallic acid as an antibacterial and anticancer agent

Drug resistance to antibacterial and anticancer drugs is one of the most important global problems in the treatment field that is constantly expanding and hinders the recovery and survival of patients. Therefore, it is necessary to identify compounds that have antibacterial and anticancer properties or increase the effectiveness of existing drugs. One of these approaches is using natural compounds that have few side effects and are effective. Gallic acid (GA) has been identified as one of the most important plant polyphenols that health-promoting effects in various aspects such as bacterial and viral infections, cancer, inflammatory, neuropsychological, gastrointestinal, and metabolic disease. Various studies have shown that GA inhibits bacterial growth by altering membrane structure, and bacterial metabolism, and inhibits biofilm formation. Also, GA inhibits cancer cell growth by targeting different signaling pathways in apoptosis, increasing reactive oxygen species (ROS) production, targeting the cell cycle, and inhibiting oncogenes and matrix metalloproteinases (MMPs) expression. Due to the powerful function of GA against bacteria and cancer cells. In this review, we describe the latest findings in the field of the sources and chemical properties of GA, its pharmacological properties and bioavailability, the antibacterial and anticancer activities of GA, and its derivatives alone, in combination with other drugs and in the form of nanoformulation. This review can be a comprehensive perspective for scientists to use medicinal compounds containing GA in future research and expand its clinical applications.

Molecular Docking Study of the C-10 Massoia Lactone Compound as an Antimicrobial and Antibiofilm Agent against Candida tropicalis

Antimicrobial resistance is now considered a global health problem because it reduces the effectiveness of antimicrobial drugs. According to the World Health Organization (WHO), the highest mortality rate is associated with infections caused by multidrug-resistant microorganisms, with approximately 700,000 deaths worldwide each year. The aim of this study was to determine the potential of C-10 massoia lactone to inhibit the growth of fungi and C. tropicalis biofilm, and molecular docking studies were performed to determine the nature of the inhibition. The study was conducted using the microdilution method for antifungal and antibiofilm testing and designed with a molecular docking approach. Furthermore, an analysis using the scanning electron microscope (SEM) was performed to evaluate the mechanism of effect. The results obtained showed that C-10 massoia lactone can inhibit the growth of fungi by 84.21% w/v. Meanwhile, the growth of C. tropicalis biofilm in the intermediate phase was 80.23% w/v and in the mature phase was 74.23% w/v. SEM results showed that C-10 massoia lactone damaged the EPS matrix of C. tropicalis so that hyphal formation was hindered due to damage to fungal cells, resulting in a decrease in attachment, density, and lysis of C. tropicalis fungal cells. Based on molecular docking tests, C-10 massoia lactone was able to inhibit biofilm formation without affecting microbial growth, while docking C-10 massoia lactone showed a significant binding and has the potential as an antifungal agent. In conclusion, the C-10 massoia lactone compound has the potential as an antibiofilm against C. tropicalis, so it can become a new antibiofilm agent.

Antibiotic-Potentiating Effect of Some Bioactive Natural Products against Planktonic Cells, Biofilms, and Virulence Factors of Pseudomonas aeruginosa

Background

Pseudomonas aeruginosa is an opportunistic human pathogen that causes infections that are mediated by both virulence factor production and biofilm formation. In addition, many antibiotics are increasingly losing their efficacy due to the development of resistance. The screening of potentially bioactive natural compounds that have both antivirulence and antibiofilm activities to enhance antibiotic efficacy and reverse antibiotic resistance is a good strategy to overcome these issues. In this study, the antibacterial, antibiofilm, and antivirulence factor activities of some bioactive natural products in combination with conventional antibiotics were evaluated against clinical isolates of P. aeruginosa.

Methods

The broth microdilution method was used to determine the antibacterial and antibiofilm activities. The checkerboard method was used to evaluate the combination interactions. Spectrophotometric and agar plate techniques were used to assess the effect of the combination on the pyocyanin production and the motility in P. aeruginosa ATCC 27853 strain.

Results

Out of the eighteen combinations tested, ten exhibited synergistic effects against planktonic cells, seven against biofilm inhibition, and five against the eradication of mature biofilm of P. aeruginosa biofilm. The best synergistic effect was the association of amikacin and sinapic acid against planktonic cells (FICI = 0.08) with a 70-fold reduction in the MIC value of amikacin. The same combination showed significant synergistic inhibition of biofilm formation (FICI = 0.1) and biofilm eradication (FICI = 0.15) reducing the MBIC and MBEC of amikacin by 32-fold. Some selected synergistic combinations showed statistically significant differences (p < 0.01 or p < 0.001) in the inhibition of virulence factors compared to the antimicrobials alone.

Conclusion

In summary, this study revealed sinapic acid as an antibiotic adjuvant and antivirulence compound to overcome P. aeruginosa infections. This finding indicates that the combinations of amikacin plus sinapic acid, ceftazidime plus thymol, and norfloxacin plus curcumin could be considered promising candidates for the development of combination therapies targeting virulence factors against P. aeruginosa infections.

Structure-dependent activity of plant natural products against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major causes for nosocomial infections and has been classified as "high priority pathogen" by the World Health Organization. Its ability to develop resistances has been a challenge for the last decades and is still a threat to health care systems, as strains with resistances to the so-called drugs of last resort have been discovered. Therefore, new antibiotics are urgently needed. Natural products are an important source for the development of new drugs, thereby mostly serving as lead compounds for further modification. In this review, the data on plant natural products with reported anti-MRSA activity until the end of 2022 is discussed, highlighting the most effective drugs with respect to their inhibitory concentrations as well as with regard to eventual synergistic effects with existing antibiotics. In the latter sense, the class of alkaloids must be mentioned, exhibiting additive or synergistic effects by inhibiting bacterial efflux pumps. With regard to the antibiotic activity, phloroglucinol derivatives certainly belong to the most promising compounds, revealing several candidates with remarkable effects, e.g., lupulone, ivesinol, rhodomyrtone, aspidinol, or hyperforin. Also, the class of terpenoids yielded noteworthy compounds, such as the sesquiterpene lactones parthenolide and lactopicrin as well as acetophenone sesquiterpenes and sphaerodiene type diterpenoids, respectively. In addition, pronounced effects were observed for the macrolide neurymenolide A and three flavonol dicoumaroylrhamnosides.

Engineering of Nisin as a Means for Improvement of Its Pharmacological Properties: A Review

Lantibiotics are believed to have a conceivable potential to be used as therapeutics, especially against clinically resistant bacterial strains. However, their low solubility and poor stability under physiological conditions limit their availability for clinical studies and further pharmaceutical commercialization. Nisin is a readily available and cheap lanthipeptide and thus serves as a good model in the search for the tools to engineer lantibiotics with improved pharmacological properties. This review aims to address technologies that can be applied to alter and enhance the antimicrobial activity, antibacterial spectrum and physicochemical properties (solubility, solution stability and protease resistance) of nisin. There are basically two general means to obtain nisin analogs-protein engineering and chemical functionalization of this antibiotic. Although bioengineering techniques have been well developed and enable the creation of nisin mutants of variable structures and properties, they are lacking spectacular effects so far. Chemical modifications of nisin based on utilization of the reactivity of its free amino and carboxylic moieties, as well as reactivity of the double bonds of its dehydroamino acids, are in their infancy.

Neobavaisoflavone Inhibits Biofilm Formation and α-Toxin Activity of Staphylococcus aureus

Neobavaisoflavone had antimicrobial activities against Gram-positive multidrug-resistant (MDR) bacteria, but the effect of neobavaisoflavone on the virulence and biofilm formation of S. aureus has not been explored. The present study aimed to investigate the possible inhibitory effect of neobavaisoflavone on the biofilm formation and α-toxin activity of S. aureus. Neobavaisoflavone presented strong inhibitory effect on the biofilm formation and α-toxin activity of both methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains at 25 µM, but did not affect the growth of S. aureus planktonic cells. Genetic mutations were identified in four coding genes, including cell wall metabolism sensor histidine kinase walK, RNA polymerase sigma factor rpoD, tetR family transcriptional regulator, and a hypothetical protein. The mutation of WalK (K570E) protein was identified and verified in all the neobavaisoflavone-induced mutant S. aureus isolates. The ASN501, LYS504, ILE544 and GLY565 of WalK protein act as hydrogen acceptors to form four hydrogen bonds with neobavaisoflavone by molecular docking analysis, and TRY505 of WalK protein contact with neobavaisoflavone to form a pi-H bond. In conclusion, neobavaisoflavone had excellent inhibitory effect on the biofilm formation and α-toxin activity of S. aureus. The WalK protein might be a potential target of neobavaisoflavone against S. aureus.