In vitro activities of licochalcone A against planktonic cells and biofilm of Enterococcus faecalis

Nature's Arsenal: Uncovering Antibacterial Agents Against Antimicrobial Resistance

Background/Objectives: Antimicrobial resistance (AMR) poses a significant public health threat, leading to increased mortality. The World Health Organization has established a priority list highlighting critical multidrug-resistant (MDR) pathogens that demand urgent research on antimicrobial treatments. Considering this and the fact that new antibiotics are only sporadically approved, natural antibacterial agents have seen a resurgence in interest as potential alternatives to conventional antibiotics and chemotherapeutics. Natural antibacterials, derived from microorganisms, higher fungi, plants, animals, natural minerals, and food sources, offer diverse mechanisms of action against MDR pathogens. Here, we present a comprehensive summary of antibacterial agents from natural sources, including a brief history of their application and highlighting key strategies for using microorganisms (microbiopredators, such as bacteriophages), plant extracts and essential oils, minerals (e.g., silver and copper), as well as compounds of animal origin, such as milk or even venoms. The review also addresses the role of prebiotics, probiotics, and antimicrobial peptides, as well as novel formulations such as nanoparticles. The mechanisms of action of these compounds, such as terpenoids, alkaloids, and phenolic compounds, are explored alongside the challenges for their application, e.g., extraction, formulation, and pharmacokinetics. Conclusions: Future research should focus on developing eco-friendly, sustainable antimicrobial agents and validating their safety and efficacy through clinical trials. Clear regulatory frameworks are essential for integrating these agents into clinical practice. Despite challenges, natural sources offer transformative potential for combating AMR and promoting sustainable health solutions.

In vitro antibacterial and antibiofilm activities of isobavachalcone against Enterococcus faecalis clinical isolates from China

BACKGROUND

The pharmacological activities of the natural product isobavachalcone, such as antimicrobial activity, reverse transcriptase blockade, and antioxidant property have been extensively reported. Whereas, its antimicrobial and biofilm-inhibitory effects on clinical E. faecalis strains in China, along with its potential mechanisms, are still not fully clear. This research is intended to assess the in vitro antibacterial and anti-biofilm effects of isobavachalcone against clinical E. faecalis isolates sourced from China. Moreover, it further explores the potential target site of it within E. faecalis.

RESULTS

It was found that the minimum inhibitory concentrations (MICs) of isobavachalcone ranged from 6.25 to 12.5 µM against 220 E. faecalis clinical strains obtained from a tertiary hospital in China. The antibiofilm activity of it with sub-MIC concentration ( 1/2 × MIC ) against the biofilm formation of E. faecalis was demonstrated and Time -killing curve assay revealed the quick bactericidal effect of isobavachalcone against E. faecalis planktonic cells. However, no synergetic bactericidal activity of isobavachalcone co-administered with vancomycin, or ampicillin was observed for eradicating the biofilm. Moreover, isobavachalcone-resistant E. faecalis was isolated by in vitro induction of isobavachalcone, and whole genome sequencing was performed to determine the genetic mutations of ten functional proteins in isobavachalcone-resistant E. faecalis, including PurH and FlgJ, with the other eight proteins being related to cell wall or cell membrane biogenesis, DNA synthesis, and energy metabolism. In addition, molecular docking results indicate that there is a potential binding of isobavachalcone and PurH protein in E. faecalis.

CONCLUSION

This research highlights the potential of isobavachalcone as a potent antibacterial agent against E. faecalis clinical isolates, capable of significantly inhibiting biofilm formation at sub-MIC concentrations. PurH protein in E. faecalis might serve as a potential target of isobavachalcone and the specific action mechanism of isobavachalcone needs further study.

Gold Nanoparticles Functionalized With 5-Amino-2-Mercaptobenzimidazole: A Promising Antimicrobial Strategy Against Carbapenem-Resistant Gram-Negative Bacteria

Introduction

Carbapenem-resistant gram-negative bacteria (CR-GNB) pose a significant threat to public health and require immediate attention. The development of novel antibacterial agents against CR-GNB has become an urgent priority, and nanomaterials offer promising solutions due to their unique properties. This study introduces 5-amino-2-mercaptobenzimidazole (5-A-2MBI) functionalized gold nanoparticles (5-A-2MBI_Au NPs) and evaluates their antibacterial activity against CR-GNB.

Methods

The 5-A-2MBI_Au NPs was synthesized using a one-pot method. Its biocompatibility, bactericidal properties, and mechanisms of action were systematically characterized through in vivo and in vitro toxicity tests, antimicrobial susceptibility testing, live/dead staining, membrane permeability and reactive oxygen species (ROS) generation assays, as well as transcriptomic analysis.

Results

The results of this study demonstrate that 5-A-2MBI_Au NPs exhibit excellent antibacterial efficacy against carbapenem-resistant gram-negative bacteria with various resistance mechanisms, with a minimum inhibitory concentration (MIC) of 2 μg/mL. In vivo experiments further confirmed that 5-A-2MBI_Au NPs not only possess effective bactericidal activity but also exhibit satisfactory biocompatibility. Mechanistic studies revealed that 5-A-2MBI_Au NPs enhance bacterial membrane permeability, increase the generation of reactive oxygen species, and disrupt intracellular oxidative stress and succinate synthesis, thereby conferring potent antibacterial activity. This study results demonstrate that 5-A-2MBI_Au NPs exhibit notable antibacterial efficacy against CR-GNB, with a minimum inhibitory concentration of 2 μg/mL. The antibacterial mechanism involves enhanced membrane permeability, increased reactive oxygen species production, and interference with intracellular oxidative stress and succinate synthesis. These mechanisms collectively contribute to the potent antibacterial activity of 5-A-2MBI_Au NPs against CR-GNB.

Discussion

5-A-2MBI_Au NPs are a novel and highly effective antibacterial agent prepared through a simple process using benzimidazole and HAuCl4•3H2O. They efficiently eradicate the most challenging multidrug-resistant GNB both in vitro and in vivo while demonstrating excellent biocompatibility. This highlights their potential as a promising antibacterial agent to combat multidrug-resistant GNB.

AMXT-1501 targets membrane phospholipids against Gram-positive and -negative multidrug-resistant bacteria

The rapid proliferation of multidrug-resistant (MDR) bacterial pathogens poses a serious threat to healthcare worldwide. Carbapenem-resistant (CR) Enterobacteriaceae, which have near-universal resistance to available antimicrobials, represent a particularly concerning issue. Herein, we report the identification of AMXT-1501, a polyamine transport system inhibitor with antibacterial activity against Gram-positive and -negative MDR bacteria. We observed minimum inhibitory concentration (MIC)50/MIC90 values for AMXT-1501 in the range of 3.13-12.5 μM (2.24-8.93 μg /mL), including for methicillin-resistant Staphylococcus aureus (MRSA), CR Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. AMXT-1501 was more effective against MRSA and CR E. coli than vancomycin and tigecycline, respectively. Subinhibitory concentrations of AMXT-1501 reduced the biofilm formation of S. aureus and Enterococcus faecalis. Mechanistically, AMXT-1501 exposure damaged microbial membranes and increased membrane permeability and membrane potential by binding to cardiolipin (CL) and phosphatidylglycerol (PG). Importantly, AMXT-1501 pressure did not induce resistance readily in the tested pathogens.

Medicinally Privileged Natural Chalcones: Abundance, Mechanisms of Action, and Clinical Trials

Chalcones have been utilized for centuries as foods and medicines across various cultures and traditions worldwide. This paper concisely overviews their biosynthesis as specialized metabolites in plants and their significance, potential, efficacy, and possibility as future medicines. This is followed by a more in-depth exploration of naturally occurring chalcones and their corresponding mechanisms of action in human bodies. Based on their mechanisms of action, chalcones exhibit many pharmacological properties, including antioxidant, anti-inflammatory, anticancer, antimalarial, antiviral, and antibacterial properties. Novel naturally occurring chalcones are also recognized as potential antidiabetic drugs, and their effect on the GLUT-4 transporter is investigated. In addition, they are examined for their anti-inflammatory effects, focusing on chalcones used for future pharmaceutical utilization. Chalcones also bind to specific receptors and toxins that prevent bacterial and viral infections. Chalcones exhibit physiological protective effects on the biological degradation of different systems, including demyelinating neurodegenerative diseases and preventing hypertension or hyperlipidemia. Chalcones that are/were in clinical trials have been included as a separate section. By revealing the many biological roles of chalcones and their impact on medicine, this paper underlines the significance of naturally occurring chalcones and their extension to patient care, providing the audience with an index of topic-relevant information.

Loratadine Derivative Lo-7: A Weapon against Drug-Resistant Enterococcus and Streptococcal Infections

The primary obstacles in the management of Enterococcus and Streptococcal infections are drug resistance and biofilm formation. Our study revealed that loratadine at a concentration of ≥25 μM exhibited significant inhibitory effects on biofilm formation in 167 clinical strains of Enterococcus faecalis and 15 clinical isolates of Streptococcus agalactiae, Streptococcus pyogenes, and Streptococcus pneumoniae. Additionally, the antibiofilm activity against E. faecalis and Streptococcal was demonstrated by several loratadine derivatives with altered side-chain carbamate moieties. This study investigated the antibacterial activity of the loratadine derivative Lo-7 against clinical strains of S. agalactiae and S. pyogenes, with minimum inhibitory concentrations ranging from 12.5 to 25 μM. The findings revealed that a low concentration of loratadine derivative Lo-7 (3.125 μM) significantly augmented the bactericidal efficacy of vancomycin against multidrug-resistant (MDR) S. agalactiae, both in vitro and in vivo. The loratadine derivative Lo-7, even at low concentrations, demonstrated significant efficacy in eliminating intracellular MDR S. agalactiae within macrophages, potentially indicating a unique advantage over vancomycin, linezolid, and loratadine. Mechanistically, exposure to the loratadine derivative Lo-7 resulted in membrane depolarization without affecting membrane permeability in S. agalactiae. The potential targeting of the SecG subunit of the SecYEG membrane-embedded channel by the loratadine derivative Lo-7 in S. agalactiae was identified through quantitative proteomics, a drug affinity responsive target stability assay, and molecular docking.

Synthesis, Antibacterial Effects, and Toxicity of Licochalcone C

Drug-resistant bacteria constitute a big barrier against current pharmacotherapy. Efforts are urgent to discover antibacterial drugs with novel chemical and biological features. Our work aimed at the synthesis, evaluation of antibacterial effects, and toxicity of licochalcone C (LCC), a naturally occurring chalcone. The synthetic route included six steps, affording a 10% overall yield. LCC showed effects against Gram-positive bacteria (MIC = 6.2-50.0 µg/mL), Mycobacterium species (MIC = 36.2-125 µg/mL), and Helicobacter pylori (MIC = 25 µg/mL). LCC inhibited the biofilm formation of MSSA and MRSA, demonstrating MBIC50 values of 6.25 μg/mL for both strains. The investigations by fluorescence microscopy, using PI and SYTO9 as fluorophores, indicated that LCC was able to disrupt the S. aureus membrane, similarly to nisin. Systemic toxicity assays using Galleria mellonella larvae showed that LCC was not lethal at 100 µg/mL after 80 h treatment. These data suggest new uses for LCC as a compound with potential applications in antibacterial drug discovery and medical device coating.

Antibacterial and anti-biofilm activity of radezolid against Staphylococcus aureus clinical isolates from China

Although the potent antibacterial ability of radezolid against Staphylococcus aureus has been widely reported worldwide, its antibacterial and anti-biofilm activity against the S. aureus clinical isolates from China remains elusive. In this study, the minimum inhibitory concentration (MIC) of radezolid was determined in S. aureus clinical isolates from China using the agar dilution method, and the relationship between radezolid susceptibility and ST distribution was also investigated. The anti-biofilm activity of radezolid against S. aureus was determined by a crystal violet assay and compared with that of linezolid and contezolid. The quantitative proteomics of S. aureus treated with radezolid was analyzed, and the genetic mutations in radezolid-induced resistant S. aureus were determined by whole-genome sequencing. The dynamic changes in transcriptional expression levels of several biofilm-related genes were analyzed by quantitative RT-PCR. Our data showed that radezolid MIC ranged from ≤0.125 to 0.5 mg/L, which was almost 1/4 × MIC of linezolid against S. aureus, indicating the greater antibacterial activity of radezolid than linezolid. The S. aureus clinical isolates with radezolid MICs of 0.5 mg/L were most widely distributed in ST239 of MRSA and ST7 of MSSA. Moreover, the more robust anti-biofilm activity of radezolid with subinhibitory concentrations (1/8 × MIC and 1/16 × MIC) was demonstrated against S. aureus when compared with that of contezolid and linezolid. Genetic mutations were found in glmS, 23S rRNA, and DUF1542 domain-containing protein in radezolid-induced resistant S. aureus selected by in vitro induction of drug exposure. Quantitative proteomic analysis of S. aureus indicated that the global expression of some biofilm-related and virulence-related proteins was downregulated. Quantitative RT-PCR further confirmed that the expressions of some downregulated biofilm-related proteins, including sdrD, carA, sraP, hlgC, sasG, spa, sspP, fnbA, and oatA, were decreased after 12 h and 24 h of exposure to radezolid. Conclusively, radezolid shows robust antibacterial and anti-biofilm activity against S. aureus clinical isolates from China when compared with contezolid and linezolid.

The potential target of bithionol against Staphylococcus aureus: design, synthesis and application of biotinylated probes Bio-A2

This study aims to explore the potential targets of bithionol in Staphylococcus aureus.The four bithionol biotinylated probes Bio-A2-1, Bio-A2-2, Bio-A2-3, and Bio-A2-4 were synthesized, the minimal inhibitory concentrations (MICs) of these probes against S. aureus were determined. The bithionol binding proteins in S. aureus were identified through immunoprecipitation and LC-MS/MS with bithionol biotinylated probe. The biotinylated bithionol probes Bio-A2-1 and Bio-A2-3 displayed antibacterial activities against S. aureus. The Bio-A2-1 showed lower MICs than Bio-A2-3, and both with the MIC₅₀/MIC₉₀ at 12.5/12.5 μM against S. aureus clinical isolates. The inhibition rates of bithionol biotinylated probes Bio-A2-1 and Bio-A2-3 on the biofilm formation of S. aureus were comparable to that of bithionol, and were stronger than that of Bio-A2-2 and Bio-A2-4. The biofilm formation of 10 out of 12S. aureus clinical isolates could be inhibited by Bio-A2-1 (at 1/4×, or 1/2× MICs). There are three proteins identified in S. aureus through immunoprecipitation and LC-MS/MS with bithionol biotinylated probe Bio-A2-1: Protein translocase subunit SecA 1 (secA1), Alanine--tRNA ligase (alaS) and DNA gyrase subunit A (gyrA), and in which the SecA1 protein the highest coverage and the most unique peptides. The LYS112, GLN143, ASP213, GLY496 and ASP498 of SecA1 protein act as hydrogen acceptors to form 6 hydrogen bonds with bithionol biotinylated probe Bio-A2-1 by molecular docking analysis. In conclusion, the bithionol biotinylated probe Bio-A2-1 has antibacterial and anti-biofilm activities against S. aureus, and SecA1 was probably one of the potential targets of bithionol in S. aureus.

In Vitro Inhibition of Growth, Biofilm Formation, and Persisters of Staphylococcus aureus by Pinaverium Bromide

Biofilm or persister cells formed by Staphylococcus aureus are closely related to pathogenicity. However, no antimicrobials exist to inhibit biofilm formation or persister cells induced by S. aureus in clinical practice. This study found that pinaverium bromide had antibacterial activity against S. aureus, with the MIC₅₀/MIC₉₀ at 12.5/25 μM, respectively. Pinaverium bromide (at 4 × MIC) showed a rapid bactericidal effect on S. aureus planktonic cells, and it was more effective (at least 1-log₁₀ cfu/mL) than linezolid, vancomycin, and ampicillin at 4 h of the time-killing test. Pinaverium bromide (at 10 × MIC) significantly inhibited the formation of S. aureus persister cells (at least 3-log₁₀ cfu/mL) than linezolid, vancomycin, and ampicillin at 24, 48, 72, 96, and 120 h of the time-killing test. Biofilm formation and adherent cells of S. aureus isolates were significantly inhibited by pinaverium bromide (at 1/2 or 1/4 × MICs). The fluorescence intensity of the membrane polarity of S. aureus increased with the treatment of pinaverium bromide (≥1 × MIC), and the MICs of pinaverium bromide increased by 4 times with the addition of cell membrane phospholipids, phosphatidyl glycerol and cardiolipin. The cell viabilities of human hepatocellular carcinoma cells HepG2 and Huh7, mouse monocyte-macrophage cells J774, and human hepatic stellate cells LX-2 were slightly inhibited by pinaverium bromide (<50 μM). There were 54 different abundance proteins detected in the pinaverium bromide-treated S. aureus isolate by proteomics analysis, of which 33 proteins increased, whereas 21 proteins decreased. The abundance of superoxide dismutase sodM and ica locus proteins icaA and icaB decreased. While the abundance of global transcriptional regulator spxA and Gamma-hemolysin component B increased. In conclusion, pinaverium bromide had an antibacterial effect on S. aureus and significantly inhibited the formation of biofilm and persister cells of S. aureus.

Licochalcone A Induces Ferroptosis in Hepatocellular Carcinoma via Reactive Oxygen Species Activated by the SLC7A11/GPX4 Pathway

Liver cancer is a common malignant tumor, and its incidence is increasing yearly. Millions of people suffer from liver cancer annually, which has a serious impact on global public health security. Licochalcone A (Lico A), an important component of the traditional Chinese herb licorice, is a natural small molecule drug with multiple pharmacological activities. In this study, we evaluated the inhibitory effects of Lico A on hepatocellular carcinoma cell lines (HepG2 and Huh-7), and explored the inhibitory mechanism of Lico A on hepatocellular carcinoma. First, we evaluated the inhibitory effects of Lico A on hepatocellular carcinoma, and showed that Lico A significantly inhibited and killed HepG2 and Huh-7 cells in vivo and in vitro. Transcriptomic analysis showed that Lico A inhibited the expression of solute carrier family 7 member 11 (SLC7A11), which induced ferroptosis. We confirmed through in vivo and in vitro experiments that Lico A promoted ferroptosis in hepatocellular carcinoma cells by downregulating SLC7A11 expression, thereby inhibiting the glutathione (GSH)-glutathione peroxidase 4 (GPX4) pathway and inducing activation of reactive oxygen species (ROS). In this study, we suggest that Lico A is a potential SLC7A11 inhibitor that induces ferroptotic death in hepatocellular carcinoma cells, thereby providing a theoretical basis for the development of natural small molecule drugs against hepatocellular carcinoma.