In Vitro and In Silico Inhibition of Staphylococcus aureus Efflux Pump NorA by α-Pinene and Limonene

Unlocking bacterial defense: Exploring the potent inhibition of NorA efflux pump by coumarin derivatives in Staphylococcus aureus

The occurrence of bacterial resistance has been increasing, compromising the treatment of various infections. The high virulence of Staphylococcus aureus allows for the maintenance of the infectious process, causing many deaths and hospitalizations. The MepA and NorA efflux pumps are transporter proteins responsible for expelling antimicrobial agents such as fluoroquinolones from the bacterial cell. Coumarins are phenolic compounds that have been studied for their diverse biological actions, including against bacteria. A pharmacokinetic in silico characterization of compounds C10, C11, C13, and C14 was carried out according to the principles of Lipinski's Rule of Five, in addition to searching for similarity in ChemBL and subsequent search for publications in CAS SciFinder. All compounds were evaluated for their in vitro antibacterial and modulatory activity against standard and multidrug-resistant Gram-positive and Gram-negative strains. The effect of coumarins C9, C10, C11, C13, and C14 as efflux pump inhibitors in Staphylococcus aureus strains was evaluated using the microdilution method (MepA or NorA) and fluorimetry (NorA). The behavior of coumarins regarding the efflux pump was determined from their interaction properties with the membrane and coumarin-protein using molecular docking and molecular dynamics simulations. Only the isolated coumarin compound C13 showed antibacterial activity against standard strains of Staphylococcus aureus and Escherichia coli. However, the other tested coumarins showed modulatory capacity for fluoroquinolone and aminoglycoside antibacterials. Compounds C10, C13, and C14 were effective in reducing the MIC of both antibiotics for both multidrug-resistant strains, while C11 potentiated the effect of norfloxacin and gentamicin for Gram-positive and Gram-negative bacteria and only norfloxacin for Gram-negative. Only coumarin C14 produced synergistic effects when associated with ciprofloxacin in MepA-carrying strains. All tested coumarins have the ability to inhibit the NorA efflux pump present in Staphylococcus aureus, both in reducing the MIC and inducing increased ethidium bromide fluorescence emission in fluorimetry. The findings of this study offer an atomistic perspective on the potential of coumarins as active inhibitors of the NorA pump, highlighting their specific mode of action mainly targeting protein inhibition. In molecular docking, it was observed that coumarins are capable of interacting with various amino acid residues of the NorA pump. The simulation showed that coumarin C10 can cross the bilayer; however, the other coumarins interacted with the membrane but were unable to cross it. Coumarins demonstrated their potentiating role in the effect of norfloxacin through a dual mechanism: efflux pump inhibition through direct interaction with the protein (C9, C10, C11, and C13) and increased interaction with the membrane (C10 and C13). In the context of pharmacokinetic prediction studies, the studied structures have a suitable chemical profile for possible oral use. We suggest that coumarin derivatives may be an interesting alternative in the future for the treatment of resistant bacterial infections, with the possibility of a synergistic effect with other antibacterials, although further studies are needed to characterize their therapeutic effects and toxicity.

Antimicrobial Activity of Individual Volatile Compounds from Various Essential Oils

Interest in natural remedies has grown recently due to a variety of public health concerns such as microbial antibiotic resistance. This global health concern necessitates innovative approaches to combat bacterial infections. Building upon established therapeutic uses of essential oils, this research focused on the volatile constituents of essential oils. The volatile antimicrobial activity of these constituents was studied by employing a derivative of a modified disk diffusion assay for quantitative comparisons. This study emphasizes the significance and value of exploring natural compounds as alternatives to traditional antibiotics and provides insights into their mechanisms and applications in contending with bacterial pathogens.

Interaction of zincite, alpha-terpineol, geranyl acetate, linalool, myrcenol, terpinolene, and thymol with virulence factors of Escherichia coli, Mycobacterium tuberculosis, Pseudomonas aeruginosa, and Staphylococcus aureus

BACKGROUND

Based on gas chromatography - mass spectrometry (GC-MS) results of a previous study, six metabolites including alpha-terpineol, geranyl acetate, linalool, myrcenol, terpinolene, and thymol showed significantly higher amounts relative to other metabolites.

METHODS

A continuation of the previous study, the interaction of these metabolites with the main virulence factors of P. aeruginosa (pseudomonas elastase and exotoxin A), Staphylococcus aureus (alpha-hemolysin and protein 2a), Mycobacterium tuberculosis (ESX-secreted protein B and the serine/threonine protein kinase), and Escherichia coli (heat-labile enterotoxin and Shiga toxin) were evaluated by molecular docking study and molecular simulation.

RESULTS

In the case of Shiga toxin, higher and lower binding affinities were related to alpha-terpinolene and zincite with values of -5.8 and -2.6 kcal/mol, respectively. For alpha-hemolysin, terpinolene and alpha-terpinolene demonstrated higher binding affinities with similar energies of -5.9 kcal/mol. Thymol and geranyl acetate showed lower binding energy of -5.7 kcal/mol toward protein 2a. Furthermore, thymol had a higher binding affinity toward heat-labile enterotoxin and ESX-secreted protein B with values of -5.9 and -6.1 kcal/mol, respectively.

CONCLUSIONS

It is concluded that the availability of secondary metabolites of A. haussknechtii surrounding zinc oxide (ZnO) NPs can hinder P. aeruginosa by inactivating Pseudomonas elastase and exotoxin.

Plant-based Natural Products as inhibitors for Efflux Pumps to Reverse Multidrug Resistance in Staphylococcus aureus: A Mini Review

Wounds provide a favourable site for microbial infection. Wound infection makes the healing more complex and does not proceed in an orchestrated manner leading to the chronic wound. Clinically infected wounds require proper antimicrobial therapy. Broad-spectrum antibiotics are usually prescribed first before going to targeted therapy. The current conventional mode of therapy mainly depends on the use of antibiotics topically or systemically. Repeated and prolonged use of antibiotics, however, leads to multidrug resistance. Staphylococcus aureus is the most common multidrugresistant microorganism found in wounds. It effectively colonizes the wound and produces many toxins, thereby reducing the host immune response and causing recurrent infection, thus making the wound more complex. The overexpression of efflux pumps is one of the major reasons for the emergence of multidrug resistance. Inhibition of efflux pumps is, therefore, a potential strategy to reverse this resistance. The effective therapy to overcome this antibiotic resistance is to use combination therapy, namely the combination of an inhibitor, and a non-antibiotic compound with an antibiotic for their dual function. Many synthetic efflux pump inhibitors to treat wound infections are still under clinical trials. In this connection, several investigations have been carried out on plant-based natural products as multidrug resistance-modifying agents as they are believed to be safe, inexpensive and suitable for chronic wound infections.

Pinus koraiensis Essential Oil Attenuates the Pathogenicity of Superbacteria by Suppressing Virulence Gene Expression

In the quest to combat infections attributable to antibiotic-resistant superbacteria, an essential oil derived from the needles of Pinus koraiensis Sieb. et Zucc. (PKEO) has emerged as a promising solution. In this study, we demonstrate that PKEO can be used to inhibit the growth, glucose metabolite acidogenicity, and biofilm formation of methicillin-resistant Staphylococcus aureus (MRSA). Quantitative PCR analysis provided direct evidence that PKEO reduces the mRNA expression of the accessory gene regulator A (agrA) and staphylococcal accessory regulator A (sarA), thereby indicating its inhibitory effect on pathogenic regulatory genes. Chromatographic analyses of PKEO identified terpene hydrocarbons as prominent essential oil constituents. These compounds, notably α-pinene, limonene, and β-caryophyllene, have been established to have antimicrobial properties. Our findings indicate that an oil derived from P. koraiensis can effectively combat antibiotic-resistant strains by disrupting the pathogenicity regulatory system, thereby establishing PKEO as a promising candidate for the treatment of MRSA infections.

3-Substituted Coumarins Inhibit NorA and MepA Efflux Pumps of Staphylococcus aureus

Coumarins are compounds with scientifically proven antibacterial properties, and modifications to the chemical structure are known to improve their effects. This information is even more relevant with the unbridled advances of antibiotic resistance, where Staphylococcus aureus and its efflux pumps play a prominent role. The study's objective was to evaluate the potential of synthetic coumarins with different substitutions in the C-3 position as possible inhibitors of the NorA and MepA efflux pumps of S. aureus. For this evaluation, the following steps took place: (i) the determination of the minimum inhibitory concentration (MIC); (ii) the association of coumarins with fluoroquinolones and ethidium bromide (EtBr); (iii) the assessment of the effect on EtBr fluorescence emission; (iv) molecular docking; and (v) an analysis of the effect on membrane permeability. Coumarins reduced the MICs of fluoroquinolones and EtBr between 50% and 87.5%. Coumarin C1 increased EtBr fluorescence emission between 20 and 40% by reinforcing the evidence of efflux inhibition. The molecular docking results demonstrated that coumarins have an affinity with efflux pumps and establish mainly hydrogen bonds and hydrophobic interactions. Furthermore, C1 did not change the permeability of the membrane. Therefore, we conclude that these 3-substituted coumarins act as inhibitors of the NorA and MepA efflux pumps of S. aureus.

Antibacterial Activity of the Essential Oil of Piper tuberculatum Jacq. Fruits against Multidrug-Resistant Strains: Inhibition of Efflux Pumps and β-Lactamase

Antimicrobial resistance has become a growing public health concern in recent decades, demanding a search for new effective treatments. Therefore, this study aimed to elucidate the phytochemical composition and evaluate the antibacterial activity of the essential oil obtained from the fruits of Piper tuberculatum Jacq. (EOPT) against strains carrying different mechanisms of antibiotic resistance. Phytochemical analysis was performed using gas chromatography-mass spectrometry (GC/MS). The antibacterial activity of EOPT and its ability to inhibit antibiotic resistance was evaluated through the broth microdilution method. The GC-MS analysis identified 99.59% of the constituents, with β-pinene (31.51%), α-pinene (28.38%), and β-cis-ocimene (20.22%) being identified as major constituents. The minimum inhibitory concentration (MIC) of EOPT was determined to assess its antibacterial activity against multidrug-resistant strains of Staphylococcus aureus (IS-58, 1199B, K2068, and K4100). The compound showed a MIC of ≥ 1024 μg/mL, suggesting a lack of intrinsic antibacterial activity. However, when the EOPT was associated with antibiotics and EtBr, a significant decrease in antibiotic resistance was observed, indicating the modulation of efflux pump activity. This evidence was corroborated with the observation of increased fluorescent light emission by the bacterial strains, indicating the involvement of the NorA and MepA efflux pumps. Additionally, the significant potentiation of ampicillin activity against the S. aureus strain K4414 suggests the β-lactamase inhibitory activity of EOPT. These results suggest that the essential oil from P. tuberculatum fruits has antibiotic-enhancing properties, with a mechanism involving the inhibition of efflux pumps and β-lactamase in MDR S. aureus strains. These findings provide new perspectives on the potential use of EOPT against antibiotic resistance and highlight the importance of Piper species as sources of bioactive compounds with promising therapeutic activities against MDR bacteria. Nevertheless, further preclinical (in vivo) studies remain necessary to confirm these in vitro-observed results.

Tackling multidrug-resistant Staphylococcus aureus by natural products and their analogues acting as NorA efflux pump inhibitors

Staphylococcus aureus (S. aureus) is a pathogen responsible for various community and hospital-acquired infections with life-threatening complications like bacteraemia, endocarditis, meningitis, liver abscess, and spinal cord epidural abscess. Antibiotics have been used to treat microbial infections since the introduction of penicillin in 1940. In recent decades, the abuse and misuse of antibiotics in humans, animals, plants, and fungi, including the treatment of non-microbial diseases, have led to the rapid emergence of multidrug-resistant pathogens with increased virulence. Bacteria have developed several complementary mechanisms to avoid the effects of antibiotics. These mechanisms include chemical transformations and enzymatic inactivation of antibiotics, modification of antibiotics' target site, and reduction of intracellular antibiotics concentration by changes in membrane permeability or by the overexpression of efflux pumps (EPs). The strategy to check antibiotic resistance includes synthesis of the antibiotic analogues, or antibiotics are given in combination with the adjuvant. The inhibitors of multidrug EPs are considered promising alternative therapeutic options with the potential to revive the effects of antibiotics and reduce bacterial virulence. Natural products played a vital role in drug discovery and significantly contributed to the area of infectious diseases. Also, natural products provide lead compounds that sometimes need modification based on structural and biological properties to meet the drug criteria. This review discusses natural products and their derived compounds as NorA efflux pump inhibitors (EPIs).

Modulation of Drug Resistance by Furanochromones in NorA Overexpressing Staphylococcus Aureus

Khellin and visnagin are natural furanochromones that photoreact with DNA. Khellin has been used in the treatment of vitiligo and psoriasis, as well as in the treatment of angina pectoris and asthma due to its potent action as a coronary vasodilator and antispasmodic agent. The present study aimed to investigate whether the compounds khellin and visnagin act as inhibitors of NorA protein, an efflux pump overproduced by the strain of Staphylococcus aureus SA-1199B that confers resistance to the fluoroquinolones, such as norfloxacin and ciprofloxacin. These substances alone did not show antibacterial activity against the strain tested. On the other hand, when these compounds were added to the culture medium at subinhibitory concentration, they were able to reduce the minimum inhibitory concentration (MIC) of norfloxacin, ethidium bromide, as well as berberine, suggesting that these compounds are modulating agents of norfloxacin resistance, possibly due to NorA inhibition. Molecular docking analysis showed that both khellin and visnagin form hydrogen bonds with Arg310, an important residue in the interaction between NorA and its substrates, supporting the hypothesis that these compounds are NorA inhibitors. These results suggest a possible application of khellin and visnagin as adjuvants to norfloxacin in the treatment of infections caused by strains of S. aureus that overproduce NorA.

An Efficient Approach for Separating Essential Oil and Polysaccharides Simultaneously from Fresh Leaves of Guajava by Microwave-Mediated Hydrodistillation with Lithium Salts and Antibacterial Activity of Essential Oil

The essential oils and polysaccharides from guava leaves have important functions. In the process of microwave extraction of plant essential oils and polysaccharides, pretreatment with lithium salts solution is helpful to increase the extraction rate. The experiment was conducted using a single factor method. Results were optimized by principal component analysis and response surface optimization. The optimal conditions were: LiCl dosage 45 μmol, microwave time 40 min, liquid-solid ratio 10, homogenization time 4.2 min, liquid-material ratio 10, and microwave irradiation power 700 W. The highest yield of essential oil and polysaccharide were 10.27 ± 0.58 mL/kg dry weight (DW) and 50.31 ± 1.88 g/kg·DW, respectively. Three verification experiments showed that the extraction rate of the microwave method was higher than that of the traditional heating method. In addition, the bacteriostatic zones reached the maximum 23.7 ± 0.11 mm when the concentration was 40 μL/mL, and the above results have practical significance.

Chalcone Derivatives as Potential Inhibitors of P-Glycoprotein and NorA: An In Silico and In Vitro Study

The human P-glycoprotein (P-gp) and the NorA transporter are the major culprits of multidrug resistance observed in various bacterial strains and cancer cell lines, by extruding drug molecules out of the targeted cells, leading to treatment failures in clinical settings. Inhibiting the activity of these efflux pumps has been a well-known strategy of drug design studies in this regard. In this manuscript, our earlier published machine learning models and homology structures of P-gp and NorA were utilized to screen a chemolibrary of 95 in-house chalcone derivatives, identifying two hit compounds, namely, F88 and F90, as potential modulators of both transporters, whose activity on Staphylococcus aureus strains overexpressing NorA and resistant to ciprofloxacin was subsequently confirmed. The findings of this study are expected to guide future research towards developing novel potent chalconic inhibitors of P-gp and/or NorA.