Gallic acid-based indanone derivative interacts synergistically with tetracycline by inhibiting efflux pump in multidrug resistant E. coli

Screening Tests for the Interaction of Rubus idaeus and Rubus occidentalis Extracts with Antibiotics against Gram-Positive and Gram-Negative Human Pathogens

WHO (World Health Organization) reports from recent years warn about the growing number of antibiotic-resistant bacterial strains. Therefore, there is an urgent need to constantly search for new substances effective in the fight against microorganisms. Plants are a rich source of chemical compounds with antibacterial properties. These compounds, classified as secondary metabolites, may act independently or support the action of currently used antibiotics. Due to the large number of metabolites isolated from the plant kingdom and new plant species being studied, there is a need to develop new strategies/techniques or modifications of currently applied methods that can be used to select plant extracts or chemical compounds isolated from them that enter into positive, synergistic interactions with currently used antibiotics. One such method is the dual-disk synergy test (DDST). It involves the diffusion of active compounds in the agar environment and influencing the growth of microorganisms grown on it. The method was used to assess the interaction of extracts from the fruit and shoots of some cultivated varieties of Rubus idaeus and Rubus occidentalis with selected antibiotics. The research was conducted on strains of bacteria pathogenic to humans, including Staphylococcus aureus, Corynebacterium diphtheriae, Escherichia coli, Pseudomonas aeruginosa, Helicobacter pylori, and Candida albicans, showing synergy, antagonism, or lack of interaction of the tested substances-plant extract and antibiotic. As a result, it was found that the diffusion method is useful in screening tests to assess the impact of antibiotic-herbal substance interactions on Gram-positive and Gram-negative microorganisms.

Synergistic Antibacterial Activity of Gallic Acid Based Chalcone Indl 2 by Inhibiting Efflux Pump Transporters

As a part of novel discovery of drugs from natural resources, present study was undertaken to explore the antibacterial potential of chalcone Indl-2 in combination with different group of antibiotics. MIC of antibiotics was reduced up to eight folds against the different cultures of E. coli by both chalcones. Among the two compounds, the i. e. 1-(3', 4,'5'-trimethoxyphenyl)-3-(3-Indyl)-prop-2-enone (6, Indl-2), a chalcone derivative of gallic acid (Indl-2) was better along with tetracycline (TET) worked synergistically and was found to inhibit efflux transporters as obvious by ethidium bromide efflux confirmed by ATPase assays and docking studies. In combination, Indl-2 kills the MDREC-KG4 cells, post-antibiotic effect (PAE) of TET was prolonged and mutant prevention concentration (MPC) of TET was also decreased. In-vivo studies revealed that Indl-2 reduces the concentration of TNF-α. In acute oral toxicity study, Indl-2 was non-toxic and well tolerated up-to dose of 2000 mg/kg. Perhaps, the study is going to report gallic acid derived chalcone as synergistic agent acting via inhibiting the primary efflux pumps.

Assessment of Genetic Diversity, Micromorphology and Antimicrobial Activity in Nepeta cataria L

The mosquito repellent Nepetalactone rich Nepeta cataria L. (catmint) plant has a variety of therapeutic and industrial potential. Reports on the genetic diversity of N. cataria germplasm are minimal globally and need attention for adding a new variety into commercial cultivation. The present study, therefore, assessed the genetic diversity among thirteen half-sib genotypes of N. cataria using agro economic and phytochemical traits. The experimental set has shown substantial variation for agro economic traits studied. Among all the studied populations, fresh herb-based essential oil content ranged from 0.1 % to 0.3 %, with a grand mean of 1.67 %. However, the estimated oil yield ranged from 44.4 kg/h to 120.73 kg/h with an average of 71.34 kg/h. Among the eleven phytochemical constituents detected in different concentrations in the essential oil of experimental sets, 4aα,7α,7aα-Nepetalactone (67.9-87.5 %) constituted the significant proportion of essential oil. Altogether, based on mean comparison, the population NC8 was found to be promising for estimated oil yield and 4aα,7α,7aα-Nepetalactone content. The greater heritability estimates (h² bs) and genetic advance as percent of mean (GAM) were observed for important economic parameters, i. e., oil content, herb yield, and oil yield. The cluster analysis revealed the least interactions between various agro economic and phytochemical variables. The microscopic study of trichome showed a positive correlation of abaxial leaf surface with essential oil content. The promising antimicrobial potential of catmint oil was also observed against human health-related pathogens. The results infer from our study provide valuable insight for genetic improvement and product development in the catmint germplasm.

Discovery of First-in-Class TAK1-MKK3 Protein-Protein Interaction (PPI) Inhibitor for the Treatment of Ulcerative Colitis through Modulating TNF-α Production

Tumor necrosis factor α (TNF-α) has been demonstrated to be a therapeutic target for autoimmune diseases. However, this biological therapy exhibits some inevitable disadvantages, such as risk of infection. Thus, small-molecule alternatives by targeting TNF-α production signaling pathway are still in demand. Herein, we describe the design, synthesis, and structure-activity relationships of 3-aryindanone compounds regarding their modulation of TNF-α production. Among them, (R)-STU104 exhibited the most potent inhibitory activity on TNF-α production, which suppressed the TAK1/MKK3/p38/MnK1/MK2/elF4E signal pathways through binding with MKK3 and disrupting the TAK1 phosphorylating MKK3. As a result, (R)-STU104 demonstrated remarkable dose-effect relationships on both acute and chronic mouse UC models. In addition to its good pharmacokinetic (PK) and safety profile, (R)-STU104 showed better anti-UC efficacy in vivo at 10 mg/kg/d than mesalazine at the dose of 50 mg/kg/d. These results suggested that TAK1-MKK3 interaction inhibitors could be potentially utilized for the treatment of UC.

Phenolic Compound Ethyl 3,4-Dihydroxybenzoate Retards Drug Efflux and Potentiates Antibiotic Activity

The World Health Organization indicated that antibiotic resistance is one of the greatest threats to health, food security, and development in the world. Drug resistance efflux pumps are essential for antibiotic resistance in bacteria. Here, we evaluated the plant phenolic compound ethyl 3,4-dihydroxybenzoate (EDHB) for its efflux pump inhibitory (EPI) activity against drug-resistant Escherichia coli. The half-maximal inhibitory concentration, modulation assays, and time-kill studies indicated that EDHB has limited antibacterial activity but can potentiate the activity of antibiotics for drug-resistant E. coli. Dye accumulation/efflux and MALDI-TOF studies showed that EDHB not only significantly increases dye accumulation and reduces dye efflux but also increases the extracellular amount of antibiotics in the drug-resistant E. coli, indicating its interference with substrate translocation via a bacterial efflux pump. Molecular docking analysis using AutoDock Vina indicated that EDHB putatively posed within the distal binding pocket of AcrB and in close interaction with the residues by H-bonds and hydrophobic contacts. Additionally, EDHB showed an elevated postantibiotic effect on drug-resistant E. coli. Our toxicity assays showed that EDHB did not change the bacterial membrane permeability and exhibited mild human cell toxicity. In summary, these findings indicate that EDHB could serve as a potential EPI for drug-resistant E. coli.

A Microbe-Derived Efflux Pump Inhibitor of the Resistance-Nodulation-Cell Division Protein Restores Antibiotic Susceptibility in Escherichia coli and Pseudomonas aeruginosa

The use of efflux pump inhibitors (EPIs) as potentiators along with the traditional antibiotics assists in the warfare against antibiotic-resistant superbugs. Efflux pumps of the resistance-nodulation-cell division (RND) family play crucial roles in multidrug resistance in Escherichia coli and Pseudomonas aeruginosa. Despite several efforts, clinically useful inhibitors are not available at present. This study describes ethyl 4-bromopyrrole-2-carboxylate (RP1) isolation, an inhibitor of RND transporters from the library of 4000 microbial exudates. RP1 acts synergistically with antibiotics by reducing their minimum inhibitory concentration in strains overexpressing archetype RND transporters (AcrAB-TolC and MexAB-OprM). It also improves the accumulation of Hoechst 33342 and inhibits its efflux (a hallmark of EPI functionality). The antibiotic-RP1 combinations prolong the postantibiotic effects and reduce the mutation prevention concentration of antibiotics. Additionally, from Biolayer Interferometry spectra, it appears that RP1 is bound to AcrB. RP1 displays low mammalian cytotoxicity, no Ca²⁺ channel inhibitory effects, and reduces the intracellular invasion of E. coli and P. aeruginosa in macrophages. Furthermore, the RP1-levofloxacin combination is nontoxic, well-tolerated, and notably effective in a murine lung infection model. In sum, RP1 is a potent EPI and worthy of further consideration as a potentiator to improve the effectiveness of existing antibiotics.

Drug resistance reversal potential of multifunctional thieno[3,2-c]pyran via potentiation of antibiotics in MDR P. aeruginosa

We explored the antibacterial potential (alone and combination) against multidrug resistant (MDR) Pseudomonas aeruginosa isolates KG-P2 using synthesized thieno[3,2-c]pyran-2-ones in combination with different antibiotics. Out of 14 compounds, two compounds (3g and 3l) abridged the MIC of tetracycline (TET) by 16 folds. Compounds was killing the KG-P2 cells, in time dependent manner, lengthened post-antibiotic effect (PAE) of TET and found decreased the mutant prevention concentration (MPC) of TET. In ethidium bromide efflux experiment, two compounds repressed the drug transporter (efflux pumps) which is further supported by molecular docking of these compounds with efflux complex MexAB-OprM. In another study, these compounds inhibited the synthesis of biofilm.

Design, synthesis and drug resistance reversal potential of novel curcumin mimics Van D: Synergy potential of curcumin mimics

Being crucial part of plant-based novel discovery of drug from natural resources, a study was done to explore the antibacterial potential of curcumin mimics in combination with antibiotics against multidrug resistant isolates of Pseudomonas aeruginosa. The best candidate Van D, a curcumin mimics reduced the MIC of tetracycline (TET) up to 16 folds against multidrug resistant clinical isolates. VanD further inhibited the efflux pumps as evident by ethidium bromide efflux and by in-silico docking studies. In another experiment, it was also found that Van D inhibits biofilm synthesis. This derivative kills the KG-P2, an isolate of P. aeruginosa in a time dependent manner, the post-antibiotic effect (PAE) of tetracycline was extended as well as mutant prevention concentration (MPC) of TET was also decreased. In Swiss albino mice, Van D reduced the proinflammatory cytokines concentration. In acute oral toxicity study, this derivative was well tolerated and found to be safe up to 1000 mg/kg dose. To the best of our knowledge, this is the first report on curcumin mimics as synergistic agent via inhibition of efflux pump.

Phytochemical Study and Antibacterial and Antibiotic Modulation Activity of Punica granatum (Pomegranate) Leaves

This study aimed to determine phytochemical contents, antibacterial properties, and antibiotic modulating potential of Punica granatum leaf extracts: hexane, chloroform, ethyl acetate, ethanol, and aqueous extracts as well as an extract enriched with total oligomer flavonoids (TOFs). The TOF extract contained the highest value of phenols and flavonoids. Rutin, luteolin, gallic acid, and ellagic acid were determined by HPLC analysis of this extract. The antibacterial activity was assayed by the disc diffusion method and microdilution method against Staphylococcus aureus and Escherichia coli standard ATCC strains and clinical isolates resistant strains. The TOF extract was the most active against all tested strains. The checkerboard method was used for the determination of synergy between two antibiotics (amoxicillin and cefotaxime) and P. granatum leaf extracts. The best synergistic interaction was found with TOF extract combined with amoxicillin for penicillin-resistant E. coli and penicillin-resistant S. aureus. These results can be assigned to tannins, flavonoids, and phenolic acids found in P. granatum leaf extracts. Pomegranate leaf extracts or active compounds isolated from these extracts could be used to fight the emergence and spread of resistant bacterial strains.

Lactobacillus rhamnosus from human breast milk shows therapeutic function against foodborne infection by multi-drug resistant Escherichia coli in mice

Lactobacillus rhamnosus shows higher therapeutic efficacy than antibiotic to treat drug-resistant E. coli infection in aspects of fast reducing coliform counts, increasing Lactobacillus amounts, and diminishing inflammation.

Comparative Drug Resistance Reversal Potential of Natural Glycosides: Potential of Synergy Niaziridin & Niazirin

Background:

Due to the limited availability of antibiotics, Gram-negative bacteria (GNB) acquire different levels of drug resistance. It raised an urgent need to identify such agents, which can reverse the phenomenon of drug resistance.

Objective:

To understand the mechanism of drug resistance reversal of glycosides; niaziridin and niazirin isolated from the pods of Moringa oleifera and ouabain (control) against the clinical isolates of multidrug-resistant Escherichia coli.

Methods:

The MICs were determined following the CLSI guidelines for broth micro-dilution. In-vitro combination studies were performed by broth checkerboard method followed by Time-Kill studies, the efflux pump inhibition assay, ATPase inhibitory activity, mutation prevention concentration and in-silico studies.

Results:

The results showed that both glycosides did not possess antibacterial activity of their own, but in combination, they reduced the MIC of tetracycline up to 16 folds. Both were found to inhibit efflux pumps, but niaziridin was the best. In real time expression pattern analysis, niaziridin was also found responsible for the down expression of the two important efflux pump acrB & yojI genes alone as well as in combination. Niaziridin was also able to over express the porin forming genes (ompA & ompX). These glycosides decreased the mutation prevention concentration of tetracycline.

Conclusion:

This is the first ever report on glycosides, niazirin and niaziridin acting as drug resistance reversal agent through efflux pump inhibition and modulation of expression pattern drug resistant genes. This study may be helpful in preparing an effective antibacterial combination against the drug-resistant GNB from a widely growing Moringa oleifera.

Antihypertensive activity of diethyl-4,4'-dihydroxy-8,3'-neolign-7,7'-dien-9,9'-dionate: A continuation study in L-NAME treated wistar rats

In the present study, we report that neolignan1 (Diethyl-4,4'-dihydroxy-8,3'-neolign-7,7'-dien-9,9'-dionate) relaxes the superior mesenteric artery in a concentration dependent manner (pD2 value 5.392 ± 0.04; n = 8 for endothelium intact and 5.204 ± 0.03; n = 8 for endothelium denuded mesenteric rings, respectively). The relaxation response of neolignan1 was found to be endothelium independent and sensitive to 1H-[1,2,4] oxadiazolo [4,3-a]quinoxalin-1-on (ODQ; 1 μM) and tetraethyl ammonium (TEA; 1 mM). In-silico studies showed good LibDock score (92.66) of neolignan1 with BK_Ca channel and are in well corroboration with ex-vivo study. Further, neolignan1 significantly decreased the systolic blood pressure, diastolic blood pressure and mean arterial pressure in the Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME; 50 mg/kg) treated Wistar rats at the dose of 30 and 100 mg/kg given once orally for 15 days. In addition, neolignan1 is well tolerated up to 100 mg/kg when given as a repeated dose, once orally for 28 days in Swiss albino mice. Neolignan1 was well absorbed from oral route, reached peak at 4 h and eliminated below detection level by 12 h after administration. Our present study concludes that neolignan1 produced relaxation in superior mesenteric artery by opening of BK_Ca channel and produced significant antihypertensive activity in L-NAME treated Wistar rats and was well tolerated by the experimental animal.

Brown and Red Seaweeds Serve as Potential Efflux Pump Inhibitors for Drug-Resistant Escherichia coli

Multidrug-resistant pathogens are a significant clinical problem. Efflux pump inhibitors (EPIs) can restore the activities of existing antibiotics by interfering with drug efflux pumps located in bacterial cell membranes. Seaweeds are important sources of biologically active metabolites of natural origin; however, their potential as EPIs remains uninvestigated. Here, functional extracts from the brown seaweeds Laminaria japonica and Sargassum horneri and the red seaweeds Gracilaria sp. and Porphyra dentata were evaluated as potential EPIs against drug-resistant Escherichia coli. All these extracts were found to potentiate the activities of drugs in modulation tests, although not to the same extent. Synergistic effects of the extracts and the drug clarithromycin were observed from the onset of Time-kill assays, with no evidence of bacterial regrowth. Ethidium bromide accumulation studies revealed that the efflux decreased in the presence of each extract, as indicated by the presence of EPIs. Most identified EPIs that have been discovered to date have aromatic structures, and the seaweed extracts were found to contain various terpenes, terpenoids, phenolic compounds, indoles, pyrrole derivatives, alkaloids, and halogenated aromatic compounds. Our study highlights the potential of these compounds of the seaweeds as drug EPIs.

Modeling the Survival of Escherichia coli O157:H7 Under Hydrostatic Pressure, Process Temperature, Time and Allyl Isothiocyanate Stresses in Ground Chicken Meat

Shiga toxin-producing Escherichia coli O157:H7 (STEC) is a common contaminant in meat and poultry. We investigated the use of non-thermal high pressure processing (HPP), with or without allyl isothiocyanate (AITC) essential oil, to kill STEC in ground chicken meat. Temperature was found an important factor affecting the inactivation of STEC in addition to pressure and process time. A full factorial experiment design (4 factors × 2 levels) was used to facilitate and evaluate the effect of pressure (250–350 MPa), operation temperature (−15–4°C), AITC concentration (0.05–0.15%, w/w), and pressure-holding time (10–20 min) on the inactivation of STEC. A linear model (a polynomial equation) was developed to predict/describe those four parameters’ impact on E. coli O157:H7 survival (R² = 0.90), as well as a dimensionless non-linear model. Both types of models were validated with data obtained from separate experimental points. The dimensionless model also demonstrated that it may predict the lethality (defined as the log CFU/g reduction of STEC before and after treatment) reasonably well with some factors set slightly outside the design ranges (e.g., a wider application than the linear model). The results provide important information regarding STEC survival as affected by HPP (e.g., pressure, time and temperature) and AITC. With the addition of AITC, the hydrostatic pressure may be lowered to the 250–350 MPa level. Regulatory agencies and food industry may use those models for STEC risk assessment in ground chicken meat. A storage test (at 4 and 10°C, 10 days) after HPP+AITC treatment indicated that AITC may continue depressing or killing the pressure-damaged cells.

Synergy of clavine alkaloid 'chanoclavine' with tetracycline against multi-drug-resistant E. coli

The emergence of multi drug resistance (MDR) in Gram-negative bacteria (GNB) and lack of novel classes of antibacterial agents have raised an immediate need to identify antibacterial agents, which can reverse the phenomenon of MDR. The purpose of present study was to evaluate synergy potential and understanding the drug resistance reversal mechanism of chanoclavine isolated from Ipomoea muricata against the multi-drug-resistant clinical isolate of Escherichia coli (MDREC). Although chanoclavine did not show antibacterial activity of its own, but in combination, it could reduce the minimum inhibitory concentration (MIC) of tetracycline (TET) up to 16-folds. Chanoclavine was found to inhibit the efflux pumps which seem to be ATPase-dependent. In real-time expression analysis, chanoclavine showed down-regulation of different efflux pump genes and decreased the mutation prevention concentration of tetracycline. Further, in silico docking studies revealed significant binding affinity of chanoclavine with different proteins known to be involved in drug resistance. In in silico ADME/toxicity studies, chanoclavine was found safe with good intestinal absorption, aqueous solubility, medium blood-brain barrier (BBB), no CYP 2D6 inhibition, no hepatotoxicity, no skin irritancy, and non-mutagenic indicating towards drug likeliness of this molecule. Based on these observations, it is hypothesized that chanoclavine might be inhibiting the efflux of tetracycline from MDREC and thus enabling the more availability of tetracycline inside the cell for its action.

Revealing the dual role of gallic acid in modulating ampicillin sensitivity of Pseudomonas aeruginosa biofilms

Aim: To understand the effects of gallic acid (GA) on ampicillin (Amp) sensitive or resistant strain of Pseudomonas sp. and also in modulating the corresponding biofilms. Methodology: The cell viability was determined by broth dilution, dry weight and CFU assays. Biofilm formation was measured by crystal violet assay while oxygen consumption rate was measured to verify the metabolic status of the cells. The membrane damage and drug efflux/accumulation were studied by fluorimetric assays. Results: GA transformed the Amp resistant cells, both planktonic and biofilms, into highly sensitive one by inducing membrane damage and enhancing accumulation of drug, whereas the Amp sensitive cells gained resistance against Amp. Conclusion: Use of GA as an antimicrobial compound should be analyzed more critically depending on the drug dosages, drug sensitivity as well as types of bacterial strains being studied.

Reversal of P-gp-mediated multidrug resistance in colon cancer by cinobufagin

Cinobufagin (CBF) is isolated from the skin and posterior auricular glands of the Asiatic toad (Bufo gargarizans). This study investigated the reversal effect of CBF on P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) in colon cancer. The effect of CBF on the cytotoxicity of anticancer drugs in P-gp overexpressing LoVo/ADR, HCT116/L, Cao-2/ADR cells and their parental cells was determined using CCK-8 assay. Apoptosis of anti-cancer drugs and accumulation of doxorubicin (DOX) and Rhodamine 123 (Rho123) in P-gp overexpressing cells were evaluated by flow cytometry. Results indicated that CBF significantly enhanced the sensitivity of P-gp substrate drugs on P-gp overexpressing cells, but had no effect on their parental cells. CBF enhanced the effect of DOX against P-gp-overexpressing LoVo/ADR cell xenografts in nude mice. Moreover, CBF also increased cell apoptosis of chemotherapy agents and intracellular accumulation of DOX and Rho123 in the MDR cells. Further research on the mechanisms revealed non-competitive inhibition of P-gp ATPase activity, but without altering the expression of P-gp. These findings demonstrated that CBF could be further developed into a safe and potent P-gp modulator for combination use with anticancer drugs in cancer chemotherapy.

Phytochemicals for human disease: An update on plant-derived compounds antibacterial activity

In recent years, many studies have shown that phytochemicals exert their antibacterial activity through different mechanisms of action, such as damage to the bacterial membrane and suppression of virulence factors, including inhibition of the activity of enzymes and toxins, and bacterial biofilm formation. In this review, we summarise data from the available literature regarding the antibacterial effects of the main phytochemicals belonging to different chemical classes, alkaloids, sulfur-containing phytochemicals, terpenoids, and polyphenols. Some phytochemicals, besides having direct antimicrobial activity, showed an in vitro synergistic effect when tested in combination with conventional antibiotics, modifying antibiotic resistance. Review of the literature showed that phytochemicals represent a possible source of effective, cheap and safe antimicrobial agents, though much work must still be carried out, especially in in vivo conditions to ensure the selection of effective antimicrobial substances with low side and adverse effects.