Theaflavin-3,3´-digallate increases the antibacterial activity of β-lactam antibiotics by inhibiting metallo-β-lactamase activity

Combining with matrine restores ciprofloxacin efficacy against qnrS producing E. coli in vitro and in vivo

The exposure risk of plasmid-mediated quinolone resistance (PMQR) genes increases the incidence of resistant bacterial infections, has resulted in clinical treatment failures with ciprofloxacin, necessitating urgent implementation of novel strategies for controlling this situation. Matrine serves as the principal constituent of the traditional Chinese herb Sophora flavescens Ait. and exhibits pharmacological activities including anti-inflammatory, antibacterial, anti-tumor, and hepatoprotective effects. However, the precise mechanism by which matrine exhibits antibacterial activity remains incompletely elucidated. This study investigated the antibacterial potential and synergistic mechanism of matrine in combination with ciprofloxacin against qnrS-carrying E. coli. The clinical ciprofloxacin-resistant E. coli carrying the qnrS and the recombinant E. coli DE3 (pET28a-qnrS) were evaluated for their antibacterial activity in vitro, it was found that the combination of matrine/ciprofloxacin exhibited a significant synergistic, reducing the MIC value of ciprofloxacin against qnrS-positive E. coli by 4-fold, and it effectively reduced the bacterial load to undetectable levels within 10 h without obvious cytotoxicity. Moreover, consistent findings were observed in significantly reducing bacterial load within the mouse infection model. Molecular docking revealed that matrine was localized in the large loop B of the qnrS crystal structure, establishing hydrogen bonds with Thr-102 and Arg-101, thereby disrupting the activity of qnrS. Interaction analysis further confirmed that matrine could significantly inhibit the protective effect of qnrS on gyrase and restore the activity of ciprofloxacin against qnrS-positive E. coli. Matrine may serve as a qnrS inhibitor to restore the efficacy of ciprofloxacin, suggesting its potential as a novel antibiotic adjuvant for controlling bacterial infections.

Kaempferol restores the susceptibility of ESBLs Escherichia coli to Ceftiofur

Introduction

The development of extended-spectrum-beta-lactamase (ESBLs) Escherichia coli (E. coli) has become a global threat to public health. An alternative strategy to alleviate this is identifying potential natural compounds to restore antibiotic activity against ESBLs E. coli. This study aimed to find a possible compound to restore ESBLs E. coli sensitivity to ceftiofur.

Methods

The synergistic effect of kaempferol and ceftiofur against ESBLs E. coli was investigated by checkerboard assays, time-kill, growth curves, and scanning electronic microscope. The impact of kaempferol with ceftiofur on the biofilm of ESBLs E. coli was evaluated by crystal violet staining and laser scanning confocal microscopy and this study also assessed the effect of kaempferol on the initial adhesion and aggregation of E. coli (SY20) by examining motility, adhesion, and surface characteristics. The RT-qPCR was used to determine the effect of kaempferol on the expression of genes related to the LuxS/AI-2 quorum sensing system in ESBLs E. coli, and the effect of kaempferol on AI-2 signaling molecules was determined by molecular docking and bioassay. The impact of kaempferol on the activity of blaCTX-M-27 protein was determined by RT-qPCR, molecular docking, and nitrofen experiments, the results were further verified by transcriptome analysis. The mouse infection model was established, and the inhibitory mechanism of kaempferol with ceftiofur on bacteria in vivo was further verified by HE staining and immunohistochemistry.

Results and discussion

Kaempferol with ceftiofur exerts synergistic antibacterial and bactericidal effects on ESBLs E. coli by influencing β-lactamase activity, biofilm formation, and LuxS/AI-2 QS system. In vivo, kaempferol protected the small intestinal villi from the damage of ESBLs E. coli. Furthermore, kaempferol fully restores the activity of ceftiofur in animal infection models by relieving the TLR4/NF-κb pathway. In conclusion, the sensitivity of ESBLs E. coli to ceftiofur in vitro and in vivo could be enhanced by kaempferol, which showed that kaempferol may be a kind of antibiotic adjuvant.

Biochar and theaflavins mitigate the antibiotic resistome and antibiotic-resistant pathogens in a soil-lettuce continuum

Antibiotic resistance can be transferred into the food chain, leading to increased risks to human health from ready-to-eat vegetables. Mitigating the transmission of antibiotic resistance from soil to vegetables by green materials is of great significance. Here, we deciphered the roles of biochar and theaflavins in mitigating antibiotic resistance genes (ARGs) and antibiotic-resistant pathogens (ARPs) in a soil-lettuce continuum. Metagenomic results showed that biochar led to a significant decrease in the abundance of ARGs in lettuce leaves, while theaflavins contributed to a significant reduction in the diversity and abundance of ARGs in soil, particularly targeting dominant ARG types such as sulfonamide and aminoglycoside resistance genes. Meanwhile, biochar and theaflavins alleviated the potential mobility of ARGs, in lettuce leaves and soil, respectively, including the spread of ARGs to human pathogens. In addition, the diversity of ARG hosts was reduced in the soil-lettuce continuum and ARPs were not detected in lettuce leaves after the application of biochar or theaflavins. Overall, this study provides a novel perspective on green materials for mitigating the antibiotic resistome and ARPs in the soil-lettuce continuum, contributing to food security and human health.

Antibacterial effect and mechanism of theaflavin against Listeria monocytogenes and its application on apple skins

Theaflavin 3,3'-digallate (TF3), a major polyphenolic component of black tea, exhibits antibacterial effects against many foodborne pathogens. However, the antibacterial mechanisms of TF3 against Listeria monocytogenes remain unclear. In this study, we investigated the effects of TF3 on viability, biofilm, and membrane function of L. monocytogenes by the conventional plating method, crystal violet staining, and microscopy using fluorescent dyes JC-1 and Laurdan, respectively. It was found that TF3 showed excellent antibacterial activity against L. monocytogenes with the minimum inhibitory concentration of 62.5 mg/L. The viable count determined on TSA decreased by 3 log after the treatment for 2 h with TF3 at 62.5 mg/L. The viable count determined on TSA containing 4% NaCl decreased by more than 4 log after the treatment for 30 min with TF3 at the same concentration, suggesting that TF3 gave damage on the cells, enhancing the antibacterial action of 4% NaCl, but the damage was recoverable in the absence of 4% NaCl. To explore the antibacterial mechanisms of TF3, the effects of TF3 on membrane potential and membrane fluidity were investigated. TF3 reduced both membrane potential and fluidity of L. monocytogenes at 62.5 mg/L, suggesting that TF3 damaged the structural integrity of the cell membrane. TF3 reduced biofilm mass of mature biofilm of L. monocytogenes. Moreover, THEAFLAVIN TF40, a commercially available Camellia sinensis leaf extract containing TF3, reduced viable count of L. monocytogenes by 2 log on apple skin. These results suggest the potential of theaflavins as a natural anti-Listeria disinfectant.

Research progress on the functions and biosynthesis of theaflavins

Theaflavins are beneficial to human health due to various bioactivities. Biosynthesis of theaflavins using polyphenol oxidase (PPO) is advantageous due to cost effectiveness and environmental friendliness. In this review, studies on the mechanism of theaflavins formation, the procedures to screen and prepare PPOs, optimization of reaction systems and immobilization of PPOs were described. The challenges associated with the mass biosynthesis of theaflavins, such as poor enzyme activity, undesirable subproducts and inclusion bodies of recombinant PPOs were presented. Further strategies to solve these challenges and improve theaflavins production, including enzyme engineering, immobilization enzyme technology, water-immiscible solvent-water biphasic systems and recombinant enzyme technology, were proposed.

Molecular docking and proteomics reveals the synergistic antibacterial mechanism of theaflavin with β-lactam antibiotics against MRSA

Recurrent epidemics of methicillin-resistant Staphylococcus aureus (S. aureus) (MRSA) have illustrated that the effectiveness of antibiotics in clinical application is rapidly fading. A feasible approach is to combine natural products with existing antibiotics to achieve an antibacterial effect. In this molecular docking study, we found that theaflavin (TF) preferentially binds the allosteric site of penicillin-binding protein 2a (PBP2a), inducing the PBP2a active site to open, which is convenient for β-lactam antibiotics to treat MRSA infection, instead of directly exerting antibacterial activity at the active site. Subsequent TMT-labeled proteomics analysis showed that TF treatment did not significantly change the landscape of the S. aureus USA300 proteome. Checkerboard dilution tests and kill curve assays were performed to validate the synergistic effect of TF and ceftiofur, and the fractional inhibitory concentration index (FICI) was 0.1875. The antibacterial effect of TF combined with ceftiofur was better than that of single-drug treatment in vitro. In addition, TF effectively enhanced the activity of ceftiofur in a mouse model of MRSA-induced pneumonia. Our findings provide a potential therapeutic strategy to combine existing antibiotics with natural products to resolve the prevalent infections of multidrug-resistant pathogens.

Antibacterial and Sporicidal Activity Evaluation of Theaflavin-3,3'-digallate

Theaflavin-3,3'-digallate (TFDG), a polyphenol derived from the leaves of Camellia sinensis, is known to have many health benefits. In this study, the antibacterial effect of TFDG against nine bacteria and the sporicidal activities on spore-forming Bacillus spp. have been investigated. Microplate assay, colony-forming unit, BacTiter-Glo^TM, and Live/Dead Assays showed that 250 µg/mL TFDG was able to inhibit bacterial growth up to 99.97%, while 625 µg/mL TFDG was able to inhibit up to 99.92% of the spores from germinating after a one-hour treatment. Binding analysis revealed the favorable binding affinity of two germination-associated proteins, GPR and Lgt (GerF), to TFDG, ranging from -7.6 to -10.3 kcal/mol. Semi-quantitative RT-PCR showed that TFDG treatment lowered the expression of gpr, ranging from 0.20 to 0.39 compared to the control in both Bacillus spp. The results suggest that TFDG not only inhibits the growth of vegetative cells but also prevents the germination of bacterial spores. This report indicates that TFDG is a promising broad-spectrum antibacterial and anti-spore agent against Gram-positive, Gram-negative, acid-fast bacteria, and endospores. The potential anti-germination mechanism has also been elucidated.

The role of flavonoids in inhibiting IL-6 and inflammatory arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that primarily affects the synovial joints. RA has well-known clinical manifestations and can cause progressive disability and premature death along with socioeconomic burdens. Interleukin-6 (IL-6) has been implicated in the pathology of RA where it can stimulate pannus formation, osteoclastogenesis, and oxidative stress. Flavonoids are plant metabolites with beneficial pharmacological effects, including anti-inflammatory, antioxidant, antidiabetic, anticancer, and others. Flavonoids are polyphenolic compounds found in a variety of plants, vegetables, and fruits. Many flavonoids have demonstrated anti-arthritic activity mediated mainly through the suppression of pro-inflammatory cytokines. This review thoroughly discusses the accumulate data on the role of flavonoids on IL-6 in RA.

Improved yield of theaflavin-3,3'-digallate from Bacillus megaterium tyrosinase via directed evolution

Theaflavin-3,3'-digallate (TFDG) in black tea possesses several health benefits. However, low TFDG yields limit its application. Herein, tyrosinases from Bacillus megaterium (Bmtyrc) were used to synthesize TFDG. To improve the catalytic efficiency of tyrosinase, a directed evolution strategy and a high-throughput screening method was employed. Compared with the wild type, mutant Bmtyrc-3 (N205D/D166E/D167G/F197W) showed 6.46 and 4.91-folds higher specific activity and 51.97- and 1.95-folds higher Vmax values towards epigallocatechin gallate (EGCG) and epicatechin gallate (ECG), respectively. Moreover, Bmtyrc-3 displayed significantly enhanced catalytic efficiencies, and the space-time yield of TFDG was 35.35 g L^-1d^-1. Bmtyrc-3 presents a broader substrate binding area, caused by a mutation (N205D) encompassing the active site. Changes in the potential of the substrate binding site and hydrogen bonds, and the electrostatic effect on the protein surface resulted in an increased activity of the substrates EGCG and ECG.

Theaflavin ameliorates renal ischemia/reperfusion injury by activating the Nrf2 signalling pathway in vivo and in vitro

Studies have demonstrated that oxidaive stress-induced apoptosis may be the main pathogenic mechanism of renal ischemia/reperfusion (I/R) injury. Theaflavin, a polyphenolic compound extracted from black tea, has been proven to exert strong antioxidant biological function. The objective of the present study was to investigate the potential role of theaflavin on renal I/R injury and its potential molecular mechanism both in vitro and in vivo. C57/BL6 J mice were used to create a model of I/R injury wherein mice were ligated with bilateral renal pedicles for 45 min, and then reperfused for 24 h. A hypoxia/reoxygenation (H/R) model of TCMK-1 cells was used to simulate I/R in vitro. Theaflavin were administered to the treatment group first and then established the model. Kidney Injury Molecule-1 (KIM-1), serum creatinine, urea nitrogen, and 24-h urinary protein levels were evaluated and changes in mitochondrial membrane potential and the ultrastructure of mitochondria were observed. Cell viability, oxidative stress damage, and apoptosis were assessed. The expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream target genes HO-1 and NQO1 were evaluated. Our results revealed that pretreatment with theaflavin significantly inhibited I/R- and H/R-induced renal injury and cell apoptosis. Theaflavin improved mitochondrial dysfunction by attenuating mitochondrial damage and promoting mitochondrial membrane potential. Theaflavin pretreatment significantly reduced malondialdehyde content, while enhancing superoxide dismutase activity in vivo and in vitro. It also reduced oxidative stress and apoptosis mainly by upregulating Nrf2 and its downstream targets in TCMK-1 cells. Thus, theaflavin exerted a protective effect against renal I/R injury by inhibiting oxidative stress and apoptosis via activation of the Nrf2-NQO1/HO-1 pathway as well as correcting mitochondrial dysfunction, thereby presenting its potential as a clinical therapeutic in cases of acute kidney injury.

β-lactamase inhibitory potential of kalafungin from marine Streptomyces in Staphylococcus aureus infected zebrafish

β-lactamase inhibitors are potent synergistic drugs to deteriorate the multidrug-resistant bacteria. Here, we report the β-lactamase inhibitory ability of kalafungin isolated from a marine sponge derived Streptomyces sp. SBRK1. The IC₅₀ value of the kalafungin was calculated as 225.37 ± 1.95 μM against β-lactamase. The enzyme kinetic analysis showed the Km value of 3.448 ± 0.7 μM and V_max value of 215.356 ± 8 μM/min and the inhibition mechanism was identified as uncompetitive type. Along with the antibacterial activity, the cell surface analysis of kalafungin treated Staphylococcus aureus cells revealed destruction of cell membrane in response to β-lactamase inhibition. Molecular docking studies have confirmed the binding property of kalafungin against β-lactamase with two hydrogen bonds. In vivo efficacy studies in the zebrafish model by green fluorescent protein expressing S. aureus infection, survival, safety and behavioral profile were reported. The toxicity and anti-infection revealed that the compound was evidently active and safe to all organs. In conclusion, this is the first report on kalafungin with β- lactamase inhibition and suggests that kalafungin may useful for synergic antibacterial therapy with β-lactam drugs to overcome β-lactamase-based resistance of any bacterial pathogens.

Discovery of a Novel Natural Allosteric Inhibitor That Targets NDM-1 Against Escherichia coli

At present, the resistance of New Delhi metallo-β-lactamase-1 (NDM-1) to carbapenems and cephalosporins, one of the mechanisms of bacterial resistance against β-lactam antibiotics, poses a threat to human health. In this work, based on the virtual ligand screen method, we found that carnosic acid (CA), a natural compound, exhibited a significant inhibitory effect against NDM-1 (IC50 = 27.07 μM). Although carnosic acid did not display direct antibacterial activity, the combination of carnosic acid and meropenem still showed bactericidal activity after the loss of bactericidal effect of meropenem. The experimental results showed that carnosic acid can enhance the antibacterial activity of meropenem against Escherichia coli ZC-YN3. To explore the inhibitory mechanism of carnosic acid against NDM-1, we performed the molecular dynamics simulation and binding energy calculation for the NDM-1-CA complex system. Notably, the 3D structure of the complex obtained from molecular modeling indicates that the binding region of carnosic acid with NDM-1 was not situated in the active region of protein. Due to binding to the allosteric pocket of carnosic acid, the active region conformation of NDM-1 was observed to have been altered. The distance from the active center of the NDM-1-CA complex was larger than that of the free protein, leading to loss of activity. Then, the mutation experiments showed that carnosic acid had lower inhibitory activity against mutated protein than wild-type proteins. Fluorescence experiments verified the results reported above. Thus, our data indicate that carnosic acid is a potential NDM-1 inhibitor and is a promising drug for the treatment of NDM-1 producing pathogens.

Ruthenium complexes as prospective inhibitors of metallo-β-lactamases to reverse carbapenem resistance

The widespread prevalence of metallo-β-lactamase (MβL)-mediated pathogens has seriously caused a loss of efficacy of carbapenem antibacterials, the last resort for the treatment of severe infectious diseases. The development of effective MβL inhibitors is an ideal alternative to restore the efficacy of carbapenems. Here we report that Ru complexes can irreversibly inhibit clinically relevant B1 subclass MβLs (NDM-1, IMP-1 and VIM-2) and potentiate meropenem efficacy against MβL-expressing bacteria in vitro and in a mice infection model. The Cys208 residue at the Zn(ii)-binding site and Met67 residue at the β-hairpin loop of an enzyme active pocket are critical for Ru complexes to inhibit NDM-1, which was verified by enzyme kinetics, thermodynamics, NDM-1-C208A mutation and MALDI-TOF-MS analysis. This study will undoubtedly aid efforts to develop metal-based MβL inhibitors in combination with carbapenems to deal with the clinical crisis of carbapenem-resistant E. coli harboring MβLs.

Application of Oleanolic Acid and Its Analogues in Combating Pathogenic Bacteria In Vitro/Vivo by a Two-Pronged Strategy of β-Lactamases and Hemolysins

The rapid spread of β-lactamase-producing bacteria in clinical practice has increasingly deteriorated the performance of β-lactam antibiotics against such resistant strains. Thus, novel agents or strategies for the war against β-lactamase-producing bacteria, especially hypervirulent resistant bacteria (such as toxin-secreting Staphylococcus aureus) carrying complex β-lactamases, are urgently needed. In this study, we found that the natural compound oleanolic acid (OA) and its analogues (especially corosolic acid (CA)) significantly inhibited the activity of important β-lactamases (NDM-1, KPC-2, and VIM-1) in Enterobacteriaceae and β-lactamases (β-lactamase N1) in S. aureus. The results showed significant synergy with β-lactams against β-lactamase-positive bacteria (fractional inhibitory concentration (FIC) index <0.5). Additionally, OA treatment significantly inhibited the activity of hemolysin from various bacteria. In the mouse infection models, the combined therapy with OA and β-lactams exhibited a significant synergistic effect in the treatment of β-lactamase-producing bacteria, as evidenced by the survival rate of S. aureus- or Escherichia coli-infected mice, which increased from 25.0 to 75.0% or from 44.4 to 61.1% (CA increased to 77.8%), respectively, compared to treatment with individual β-lactams. Although OA treatment alone led to systemic protection against S. aureus-infected mice by directly targeting α-hemolysin (Hla), a relatively better therapeutic effect was observed for the combined therapy. To the best of our knowledge, this study is the first to find effective inhibitors against resistant bacterial infections with a two-pronged strategy by simultaneously targeting resistance enzymes and toxins, which may provide a promising therapeutic strategy for drug-resistant bacterial infections.

Specific NDM-1 Inhibitor of Isoliquiritin Enhances the Activity of Meropenem against NDM-1-positive Enterobacteriaceae in vitro

NDM-1-positive Enterobacteriaceae have caused serious clinical infections, with high mortality rates. Carbapenem was the ultimate expectation for the treatment of such infections in clinical practice. However, since the discovery of plasmid-mediated New Delhi metallo-β-lactamase-1 (NDM-1), the efficient therapeutic effects of carbapenems have been increasingly restricted. Here, we identified isoliquiritin, a novel specific inhibitor of the NDM-1 enzyme that restored the activity of carbapenem against NDM-1-producing E. coli isolates and K. pneumoniae isolates without affecting the growth of bacteria. A checkerboard test, growth curve assays and time-kill assays confirmed the significant synergistic effect of isoliquiritin combined with meropenem in vitro. It is worth noting that isoliquiritin only inhibited the activity of NDM-1 and had no obvious inhibitory effect on other class B metallo-β-lactamases (VIM-1) or NDM-1 mutants (NDM-5). The FIC indices of meropenem with isoliquiritin on NDM-1-positive E. coli and K. pneumoniae were all less than 0.5. Isoliquiritin had no influences on the expression of NDM-1-positive strains at concentrations below 64 µg/mL. Collectively, our results show that isoliquiritin is a potential adjuvant therapy drug that could enhance the antibacterial effect of carbapenems, such as meropenem, on NDM-1-positive Enterobacteria and lay the foundation for subsequent clinical trials.

Palmatine Is a Plasmid-Mediated Quinolone Resistance (PMQR) Inhibitor That Restores the Activity of Ciprofloxacin Against QnrS and AAC(6')-Ib-cr-Producing Escherichia coli

Purpose

The emergence of plasmid-mediated quinolone resistance (PMQR) is a global challenge in the treatment of clinical disease in both humans and animals and is exacerbated by the presence of different PMQR genes existing in the same bacterial strain. Here, we discovered that a natural isoquinoline alkaloid palmatine extracted from traditional Chinese medicinal plants effectively inhibited the activity of PMQR proteins QnrS and AAC(6′)-Ib-cr.

Methods

In total 120 clinical ciprofloxacin-resistant Escherichia coli (E. coli) were screened for the presence of qnrS and aac(6ʹ)-Ib-cr by PCR. Recombinant E. coli that produced QnrS or AAC(6ʹ)-Ib-cr proteins were constructed and the correct expression was confirmed by MALDI/TOF MS analysis and SDS-PAGE. A minimal inhibitory concentration (MICs) assay, growth curve assay and time-kill assay were conducted to evaluate the in vitro antibacterial activity of palmatine and the combination of palmatine and ciprofloxacin. Cytotoxicity assays and mouse thigh infection model were used to evaluate the in vivo synergies. Molecular docking, gyrase supercoiling assay and acetylation assay were used to clarify the mechanism of action.

Results

Palmatine effectively restored the activity of ciprofloxacin against qnrS and aac(6ʹ)-Ib-cr-positive E. coli strains in a synergistic manner in vitro. In addition, the combined therapy significantly reduced the bacterial burden in a mouse thigh infection model. Molecular docking revealed that palmatine bound at the functional large loop B of QnrS and Trp102Arg and Asp179Tyr in the binding pocket of AAC(6′)-Ib-cr. Furthermore, interaction analysis confirmed that palmatine reduced the gyrase protective effect of QnrS and the acetylation effect of AAC(6′)-Ib-cr.

Conclusion

Our findings suggest that palmatine is a potential efficacious compound to restore PMQR-mediated ciprofloxacin resistance and warrants further preclinical evaluations.

Isoalantolactone Enhances the Antimicrobial Activity of Penicillin G against Staphylococcus aureus by Inactivating β-lactamase during Protein Translation

β-Lactamase-positive Staphylococcus aureus is one of the most prevalent multidrug-resistant pathogens worldwide and is associated with increasing threats to clinical therapeutics and public health. Here, we showed that isoalantolactone (IAL), in combination with penicillin G, exhibited significant synergism against 21 β-lactamase-positive S. aureus strains (including methicillin resistant S. aureus). An enzyme inhibition assay, a checkerboard minimum inhibitory concentration (MIC) assay, a growth curve assay, a time-killing assay, a RT-PCR assay and Circular Dichroism (CD) spectroscopy were performed on different β-lactamases or β-lactamase-positive S. aureus strains, in vitro, to confirm the mechanism of inhibition of β-lactamase and the synergistic effects of the combination of penicillin G and IAL. All the fractional inhibitory concentration (FIC) indices of penicillin G, in combination with IAL, against β-lactamase-positive S. aureus, were less than 0.5, and ranged from 0.10 ± 0.02 to 0.38 ± 0.17. The survival rate of S. aureus-infected mice increased significantly from 35.29% to 88.24% within 144 h following multiple compound therapy approaches. Unlike sulbactam, IAL inactivated β-lactamase during protein translation, and the therapeutic effect of combination therapy with IAL and penicillin G was equivalent to that of sulbactam with penicillin G. Collectively, our results indicated that IAL is a promising and leading drug that can be used to restore the antibacterial effect of β-lactam antibiotics such as penicillin G and to address the inevitable infection caused by βlactamase-positive S. aureus.

Theaflavin-3,3´-digallate increases the antibacterial activity of β-lactam antibiotics by inhibiting metallo-β-lactamase activity

Metallo-β-lactamases (MBLs) are some of the best known β-lactamases produced by common Gram-positive and Gram-negative pathogens and are crucial factors in the rise of bacterial resistance against β-lactam antibiotics. Although many types of β-lactamase inhibitors have been successfully developed and used in clinical settings, no MBL inhibitors have been identified to date. Nitrocefin, checkerboard and time-kill assays were used to examine the enzyme behaviour in vitro. Molecular docking calculation, molecular dynamics simulation, calculation of the binding free energy and ligand-residue interaction decomposition were used for mechanistic research. The behaviour of the enzymes in vivo was investigated by a mouse infection experiment. We showed that theaflavin-3,3´-digallate (TFDG), a natural compound lacking antibacterial activities, can inhibit the hydrolysis of MBLs. In the checkerboard and time-kill assays, we observed a synergistic effect of TFDG with β-lactam antibiotics against methicillin-resistant Staphylococcus aureus BAA1717. Molecular dynamics simulations were used to identify the mechanism of the inhibition of MBLs by TFDG, and we observed that the hydrolysis activity of the MBLs was restricted by the binding of TFDG to Gln242 and Ser369. Furthermore, the combination of TFDG with β-lactam antibiotics showed effective protection in a mouse Staphylococcus aureus pneumonia model. These findings suggest that TFDG can effectively inhibit the hydrolysis activity of MBLs and enhance the antibacterial activity of β-lactam antibiotics against pathogens in vitro and in vivo.