Inhibition of the MepA efflux pump by limonene demonstrated by in vitro and in silico methods

Antibacterial, bacteriolytic, antibiofilm, and synergistic effects of the peel oils of Citrus microcarpa and Citrus x amblycarpa with tetracycline against foodborne Escherichia coli

Citrus essential oils (EOs) have shown significant antibacterial activity. The present study was undertaken to evaluate the antibacterial activity of the peel oils of Citrus microcarpa and C. x amblycarpa against Escherichia coli. The minimum inhibition concentration (MIC) was determined by using the broth microdilution assay. The checkerboard method was used to identify synergistic effects of the EOs with tetracycline, while bacteriolysis was assessed by calculating the optical density of the bacterial supernatant, crystal violet assay was used to assess their antibiofilm. Ethidium bromide accumulation test was employed to assess efflux pump inhibition. Electron microscope analysis was performed to observe its morphological changes. The EOs of C. microcarpa and C. x amblycarpa were found to contain D-limonene major compound at 55.78% and 46.7%, respectively. Citrus microcarpa EOs exhibited moderate antibacterial against E. coli with a MIC value of 200 μg/mL. The combination of C. microcarpa oil (7.8 μg/mL) and tetracycline (62.5 μg/mL) exhibited a synergy with FICI of 0.5. This combination inhibited biofilm formation and disrupt bacterial cell membranes. Citrus microcarpa EOs blocked the efflux pumps in E. coli. Citrus microcarpa EOs demonstrated promising antibacterial activity, which can be further explored for the development of drugs to combat E. coli.

In vitro and in silico evidences about the inhibition of MepA efflux pump by coumarin derivatives

The discovery of antibiotics has significantly transformed the outcomes of bacterial infections in the last decades. However, the development of antibiotic resistance mechanisms has allowed an increasing number of bacterial strains to overcome the action of antibiotics, decreasing their effectiveness against infections they were developed to treat. This study aimed to evaluate the antibacterial activity of synthetic coumarins Staphylococcus aureus in vitro and analyze their interaction with the MepA efflux pump in silico. The Minimum Inhibitory Concentration (MIC) determination showed that none of the test compounds have antibacterial activity. However, all coumarin derivatives decreased the MIC of the standard efflux inhibitor ethidium bromide, indicating antibacterial synergism. On the other hand, the C14 derivative potentiated the antibacterial activity of ciprofloxacin against the resistant strain. In silico analysis showed that C9, C11, and C13 coumarins showed the most favorable interaction with the MepA efflux pump. Nevertheless, due to the present in silico and in vitro investigation limitations, further experimental research is required to confirm the therapeutic potential of these compounds in vivo.

Terpenes as bacterial efflux pump inhibitors: A systematic review

Managing antibiotic resistance is a significant challenge in modern pharmacotherapy. While molecular analyses have identified efflux pump expression as an essential mechanism underlying multidrug resistance, the targeted drug development has occurred slower. Thus, considering the verification that terpenes can enhance the activity of antibiotics against resistant bacteria, the present study gathered evidence pointing to these natural compounds as bacterial efflux pump inhibitors. A systematic search for manuscripts published between January 2007 and January 2022 was carried out using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol and the following search terms: “Terpene”; AND “Efflux pump”; and “Bacteria.” From a total of 101 articles found in the initial search, 41 were included in this review. Seventy-five different terpenes, 63 bacterial strains, and 22 different efflux pumps were reported, with carvacrol, Staphylococcus aureus SA-1199B, and NorA appearing most frequently mentioned terpene, bacterial strain, and efflux pump (EP), respectively. The Chi-Squared analysis indicated that terpenes are significantly effective EP inhibitors in Gram-positive and Gram-negative strains, with the inhibitory frequency significantly higher in Gram-positive strains. The results of the present review suggest that terpenes are significant efflux pump inhibitors and, as such, can be used in drug development targeting the combat of antibacterial resistance.

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.

Efflux Pump Mediated Antimicrobial Resistance by Staphylococci in Health-Related Environments: Challenges and the Quest for Inhibition

The increasing emergence of antimicrobial resistance in staphylococcal bacteria is a major health threat worldwide due to significant morbidity and mortality resulting from their associated hospital- or community-acquired infections. Dramatic decrease in the discovery of new antibiotics from the pharmaceutical industry coupled with increased use of sanitisers and disinfectants due to the ongoing COVID-19 pandemic can further aggravate the problem of antimicrobial resistance. Staphylococci utilise multiple mechanisms to circumvent the effects of antimicrobials. One of these resistance mechanisms is the export of antimicrobial agents through the activity of membrane-embedded multidrug efflux pump proteins. The use of efflux pump inhibitors in combination with currently approved antimicrobials is a promising strategy to potentiate their clinical efficacy against resistant strains of staphylococci, and simultaneously reduce the selection of resistant mutants. This review presents an overview of the current knowledge of staphylococcal efflux pumps, discusses their clinical impact, and summarises compounds found in the last decade from plant and synthetic origin that have the potential to be used as adjuvants to antibiotic therapy against multidrug resistant staphylococci. Critically, future high-resolution structures of staphylococcal efflux pumps could aid in design and development of safer, more target-specific and highly potent efflux pump inhibitors to progress into clinical use.

Stress impact of liposomes loaded with ciprofloxacin on the expression level of MepA and NorB efflux pumps of methicillin-resistant Staphylococcus aureus

One mechanism of ciprofloxacin resistance is attributed to chromosomal DNA-encoded efflux pumps such as the MepA and NorB proteins. The goal of this research is to find a way to bypass Staphylococcus aureus' efflux pumps. Because of its high membrane permeability and low association with NorB and MepA efflux proteins, a liposome-encapsulating antibiotic is one of the promising, cost-effective drug carriers and coating mechanisms for overcoming active transport of methicillin-resistant S. aureus (MRSA) multidrug-resistant efflux protein . The calculated "Log Perm RRCK" membrane permeability values of 1,2-distearoyl-sn-glycerol-3-phosphocholine (DSPC) ciprofloxacin liposome-encapsulated (CFL) showed a lower negative value of - 4,652 cm/s and greater membrane permeability than ciprofloxacin free (CPF). The results of RT-qPCR showed that cationic liposomes containing ciprofloxacin in liposome-encapsulated form (CFL) improved CPF antibacterial activity and affinity for negatively charged bacterial cell surface membrane in comparison to free drug and liposome, as it overcame several resistance mechanisms and reduced the expression of efflux pumps. Ciprofloxacin liposome-encapsulated (CFL) is therefore more effective than ciprofloxacin alone. Liposomes can be combined with a variety of drugs that interact with bacterial cell efflux pumps to maintain high sustained levels of antibiotics in bacterial cells.