Analysis and antibacterial activity of Nigella sativa essential oil formulated in microemulsion system

The Emergence of N. sativa L. as a Green Antifungal Agent

BACKGROUND

Nigella sativa L. has been widely used in the Unani, Ayurveda, Chinese, and Arabic medicine systems and has a long history of medicinal and folk uses. Several phytoconstituents of the plant are reported to have excellent therapeutic properties. In-vitro and in-vivo studies have revealed that seed oil and thymoquinone have excellent inhibitory efficacy on a wide range of both pathogenic and non-pathogenic fungi.

OBJECTIVE

The present review aims to undertake a comprehensive and systematic evaluation of the antifungal effects of different phytochemical constituents of black cumin.

METHOD

An exhaustive database retrieval was conducted on PubMed, Scopus, ISI Web of Science, SciFinder, Google Scholar, and CABI to collect scientific information about the antifungal activity of N. sativa L. with 1990 to 2023 as a reference range using 'Nigella sativa,' 'Nigella oil,' 'antifungal uses,' 'dermatophytic fungi,' 'candidiasis,' 'anti-aflatoxin,' 'anti-biofilm' and 'biological activity' as the keywords.

RESULTS

Black cumin seeds, as well as the extract of aerial parts, were found to exhibit strong antifungal activity against a wide range of fungi. Among the active compounds, thymoquinone exhibited the most potent antifungal effect. Several recent studies proved that black cumin inhibits biofilm formation and growth.

CONCLUSION

The review provides an in-depth analysis of the antifungal activity of black cumin. This work emphasizes the need to expand studies on this plant to exploit its antifungal properties for biomedical applications.

Nanoemulsion as an Effective Inhibitor of Biofilm-forming Bacterial Associated Drug Resistance: An Insight into COVID Based Nosocomial Infections

Antibiotic overuse has resulted in the microevolution of drug-tolerant bacteria. Understandably it has become one of the most significant obstacles of the current century for scientists and researchers to overcome. Bacteria have a tendency to form biofilm as a survival mechanism. Biofilm producing microorganism become far more resistant to antimicrobial agents and their tolerance to drugs also increases. Prevention of biofilm development and curbing the virulency factors of these multi drug resistant or tolerant bacterial pathogens is a newly recognised tactic for overcoming the challenges associated with such bacterial infections and has become a niche to be addressed. In order to inhibit virulence and biofilm from planktonic bacteria such as, Pseudomonas aeruginosa, Acinetobacter baumannii, and others, stable nanoemulsions (NEs) of essential oils (EOs) and their bioactive compounds prove to be an interesting solution. These NEs demonstrated significantly greater anti-biofilm and anti-virulence activity than commercial antibiotics. The EO reduces disease-causing gene expression, which is required for pathogenicity, biofilm formation and attachment to the surfaces. Essential NE and NE-loaded hydrogel surface coatings demonstrates superior antibiofilm activity which can be employed in healthcare-related equipments like glass, plastic, and metal chairs, hospital beds, ventilators, catheters, and tools used in intensive care units. Thus, anti-virulence and anti-biofilm forming strategies based on NEs-loaded hydrogel may be used as coatings to combat biofilm-mediated infection on solid surfaces.

Comparative Analysis of the Antimicrobial Activity of Essential Oils and Their Formulated Microemulsions against Foodborne Pathogens and Spoilage Bacteria

The antimicrobial activity of several essential oils (EOs) and their related microemulsions (MEs) was investigated. EOs were obtained from Cannabis sativa L. cv CS (C. sativa), Carum carvi L. (C. carvi), Crithmum maritimum L. (C. maritimum), Cuminum cyminum L. (C. cyminum), x Cupressocyparis leylandii A.B. Jacks & Dallim. (C. leylandii), Cupressus arizonica Greene (C. arizonica), Ferula assa-foetida L. (F. assa-foetida)., Ferula gummosa Boiss. (F. gummosa), Juniperus communis L. (J. communis), Juniperus x pfitzeriana (Spath) P.A. Schmidt (J. pfitzeriana), Pimpinella anisum L (P. anisum). Preliminary screening revealed that Cuminum cyminum, Crithmum maritimum, and Pimpinella anisum (10% v/v) were effective against all tested microorganisms (Escherichia coli ATCC 35218, Listeria monocytogenes ATCC 7644, Staphylococcus aureus ATCC 29213, Pseudomonas fluorescens DSM 4358, and Candida albicans ATCC 10231), with growth inhibition diameter from 10 to 25 mm. These EOs were used to formulate the MEs with an average size < 50 nm and a good stability over 30 days. EOs’ antimicrobial activity was further enhanced in the MEs, with a generalized lowering of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values. C. cyminum-ME reached, in most cases, MIC two times lower (0.312%) than the corresponding EO (0.625%) and even eight times lower against S. aureus (0.156 vs. 1.25%). A more remarkable microbicide effect was noted for C. cyminum-ME, with MBC values eight times lower (from 0.312 to 0.625%) than the corresponding EO (from 2.5 to 5%). Overall, MEs resulted in an efficient system for EOs encapsulation, enhancing solubility and lowering concentration to exert antimicrobial efficacy.

Microemulsion Delivery System Improves Cellular Uptake of Genipin and Its Protective Effect against Aβ1-42-Induced PC12 Cell Cytotoxicity

Genipin has attracted much attention for its hepatoprotective, anti-inflammatory, and neuroprotection activities. However, poor water solubility and active chemical properties limit its application in food and pharmaceutical industries. This article aimed to develop a lipid-based microemulsion delivery system to improve the stability and bioavailability of genipin. The excipients for a genipin microemulsion (GME) preparation were screened and a pseudo-ternary phase diagram was established. The droplet size (DS), zeta potential (ZP), polydispersity index (PDI), physical and simulated gastrointestinal digestion stability, and in vitro drug release properties were characterized. Finally, the effect of the microemulsion on its cellular uptake by Caco-2 cells and the protective effect on PC12 cells were investigated. The prepared GME had a transparent appearance with a DS of 16.17 ± 0.27 nm, ZP of −8.11 ± 0.77 mV, and PDI of 0.183 ± 0.013. It exhibited good temperature, pH, ionic strength, and simulated gastrointestinal digestion stability. The in vitro release and cellular uptake data showed that the GME had a lower release rate and better bioavailability compared with that of free genipin. Interestingly, the GME showed a significantly better protective effect against amyloid-β (Aβ1-42)-induced PC12 cell cytotoxicity than that of the unencapsulated genipin. These findings suggest that the lipid-based microemulsion delivery system could serve as a promising approach to improve the application of genipin.

Cytotoxic, apoptotic, and genetic evaluations of Nigella sativa essential oil nanoemulsion against human hepatocellular carcinoma cell lines

Background

Phytochemicals and plant extracts are showing promising anticancer potentials. In the current study, the volatile faction (essential oil) of Nigella sativa seeds was evaluated against some hepatocellular carcinoma (HCC). The essential oil was extracted and characterized by chromatographic techniques to reveal its chemical composition, especially thymoquinone. Then, the oil was fabricated in two nanoemulsion formulations (F1 and F2), which differ in their composition of surfactants. The cytotoxicity and apoptotic activities of the essential oil and its nanoemulsions were evaluated in vitro against HepG2 and Huh-7 cell lines. Normal WI-38 cell line was also included in that evaluation to study the selectivity and safety of the different formulations on normal cells.

Results

Gas chromatographic analysis indicated that the essential oil is composed mainly of p-cymene (40.0%), thymoquinone (31.2%) and trans-α-thujene (12.8%). Particle size of the nanoemulsions ranged between 9.4 and 119.7 nm depending on the type of surfactant used in the formulation process. The pure essential oil and its two nanoemulsions (F1 and F2) showed dose-dependent antiproliferative activity against both HCC cells. This activity reached its highest cell inhibition in the case of nanoemulsion (F2) where the proliferation percentage was only 21.9% and 9.2% against HepG2 and Huh-7 cells, respectively. The same nanoemulsion (F2) also showed the lowest IC50 values (55.7 and 35.5 µg/ml) against both HepG2 and Huh-7 cells, respectively, compared to 100 µg/ml for the reference drug Doxorubicin. Flow cytometric analysis also confirmed that nanoemulsion (F2) has the highest apoptotic activity compared to nanoemulsion (F1) and the pure unformulated essential oil. Genetic expressions of pro-apoptotic (Bax) and the anti-apoptotic (Bcl-2) gene markers evaluation revealed that nanoemulsion (F2) has better activity in upregulating (Bax) and down-regulate (Bcl-2) with the highest Bax/Bcl-2 ratio (69) was found against Huh-7 cells. All N. sativa nanoemulsions showed minimal cytotoxicity on the normal WI-38 cell, indicating wide safety margins due to selective properties.

Conclusion

Overall, the study revealed the potentials of N. sativa essential oil, after formulation in specially tailored nanoemulsion for application as potential adjuvant liver anticancer agent.

Graphical Abstract

Bioactive Compounds of Nigella Sativa Essential Oil as Antibacterial Agents against Chlamydia Trachomatis D

Urogenital tract infection caused by obligate intracellular bacterium Chlamydia trachomatis D (CtrD) is a leading cause of sexually transmitted diseases. Essential oil (EO) of Nigella sativa has a broad antimicrobial spectrum. The aim of this study was to evaluate the antimicrobial activity of the bioactive compounds (p-cymene, thymoquinone, carvacrol, and thymol) of N. sativa EO against CtrD. The cytotoxic effects of the compounds were determined by MTT assay. In order to quantify the anti-chlamydial activity of the compounds, HeLa cells were infected with CtrD or CtrD treated previously with the compounds. The titer of the infectious CtrD was determined by indirect immunofluorescence assay. The minimum inhibitory concentrations of the compounds were evaluated by direct quantitative PCR. None of the compounds showed a cytotoxic effect on HeLa cells in the concentrations tested. According to the immunofluorescence assay, all of the compounds significantly inhibited the growth of CtrD. The quantitative PCR revealed that the minimum concentration that exerted anti-chlamydial activity was 3.12 µM in the case of thymoquinone and p-cymene, while that of carvacrol and thymol was 6.25 µM. Therefore, it can be concluded that bioactive compounds of N. sativa EO could be used as effective antimicrobial agents against CtrD.

Activity of preparations from Spilanthes oleracea, propolis, Nigella sativa, and black garlic on different microorganisms involved in oral diseases and on total human salivary bacteria: A pilot study

Due to continuous rise in antibiotic resistance, there is a need for alternative treatment options to reduce the levels of oral pathogens for the maintenance of oral as well as overall health. The aim of this study was to evaluate the in vitro antibacterial potential of tinctures of Spilanthes oleracea and propolis, Nigella seed oil, and an ethanolic extract of black garlic on microorganisms involved in oral diseases. Both the minimum inhibitory concentration assay and the minimum bactericidal/fungicidal concentration assay were used in this study. Inhibition effects against total human salivary bacteria were also determined. Our results show that all of the preparations tested had potent antimicrobial activities. When measured 10 min after exposure, even low concentrations of the propolis tincture were found to have killed more than 99% of salivary bacteria, whereas Spilanthes tincture and black garlic extract killed more than 90% and Nigella seed oil more than 60% of the pathogens. This suggests that all preparations are promising candidates for the use in oral health care products and that all have the potential to control biofilm associated infections.

Formulation, characterization and antimicrobial properties of black cumin essential oil nanoemulsions stabilized by OSA starch

Preparation of oil-in-water nanoemulsions has emerged as a subject of interest for the encapsulation of lipophilic functional ingredients to increase their stability and activity. In this study, black cumin essential oil nanoemulsions (BCO-NE) using different ratios of essential oil with canola and flax seed oils (ripening inhibitors) were formulated and stabilized with octenyl succinic anhydride (OSA) modified waxy maize starch. The nanoemulsions exhibited monomodal size distributions with mean droplet diameter below 200 nm and zeta potential above -30, indicating a strong electrostatic repulsion between the dispersed oil droplets. Further, during storage (4 weeks at 25 °C ± 2) emulsions showed shear thinning phenomena and stability towards coalescence. Antimicrobial properties of nanoemulsions were determined by minimum inhibitory concentration and time-kill method against two Gram-positive bacterial (GPB) strains (Bacillus cereus and Listeria monocytogenes). Negatively charged BCO-NE showed prolonged bactericidal activities as compared to pure BCO due to better stability, controlled release and self-assembly with GPB cell membrane followed by destruction of cellular constituents. Our results suggest the application of BCO-NE may be exploited in aqueous food systems for extending the shelf life and other functional properties.

Finding Novel Antibiotic Substances from Medicinal Plants - Antimicrobial Properties of Nigella Sativa Directed against Multidrug-resistant Bacteria

The progressive rise in multidrug-resistant (MDR) bacterial strains poses serious problems in the treatment of infectious diseases. While the number of newly developed antimicrobial compounds has greatly fallen, the resistance of pathogens against commonly prescribed drugs is further increasing. This rise in resistance illustrates the need for developing novel therapeutic and preventive antimicrobial options. The medicinal herb Nigella sativa and its derivatives constitute promising candidates. In a comprehensive literature survey (using the PubMed data base), we searched for publications on the antimicrobial effects of N. sativa particularly directed against MDR bacterial strains. In vitro studies published between 2000 and 2015 revealed that N. sativa exerted potent antibacterial effects against both Gram-positive and Gram-negative species including resistant strains. For instance, N. sativa inhibited the growth of bacteria causing significant gastrointestinal morbidity such as Salmonella, Helicobacter pylori, and Escherichia coli. However, Listeria monocytogenes and Pseudomonas aeruginosa displayed resistance against black cumin seed extracts. In conclusion, our literature survey revealed potent antimicrobial properties of N. sativa against MDR strains in vitro that should be further investigated in order to develop novel therapeutic perspectives for combating infectious diseases particularly caused by MDR strains.

Essential oil micro- and nanoemulsions: promising roles in antimicrobial therapy targeting human pathogens

Antimicrobial resistance is a major health concern worldwide. A narrowing of the antibiotic development pipeline and a resurgence in public opinion towards 'natural' therapies have renewed the interest in using essential oils as antimicrobial agents. The drawbacks of bulk dosing of essential oils can be mitigated by formulating them as micro- and nanoemulsions. These emulsions have an added advantage as they are in the nanometre size range whose thermodynamic properties enable them to be used as an effective drug delivery system. This review describes the current work on the antimicrobial activities of essential oil micro- and nanoemulsions and their role as drug delivery vehicles.

Assessment of In vitro Antibacterial Activity and Cytotoxicity Effect of Nigella sativa Oil

BACKGROUND

Methicillin resistance is a serious health concern since it has spread among Staphylococcus aureus and coagulase-negative Staphylococci (CoNS) that are frequent community and nosocomial pathogens worldwide. Methicillin-resistant strains are often resistant to other classes of antibiotics, making their treatment difficult. Nigella sativa oil is known to be active against Gram-positive cocci, yet its in vitro cytotoxicity is rarely investigated, is a proper and powerful candidate for treatment of methicillin-resistant isolates.

OBJECTIVES

The aim of this study is to evaluate the in vitro antibacterial activity and cytotoxicity effect of N. sativa oil.

MATERIALS AND METHODS

The minimal inhibitory concentrations (MICs) of N. sativa oil were determined by broth microdilution method against four different American Type Culture Collection strains, 45 clinical isolates of methicillin-resistant S. aureus (MRSA), and 77 methicillin-resistant CoNS (MRCoNS). The effects of different dilutions (0.25 μg/mL, 0.5 μg/mL, and 1 μg/mL) of N. sativa oil on the proliferation of gingival fibroblasts were evaluated.

RESULTS

The MIC values of N. sativa oil against clinical isolates of Staphylococci were between <0.25 μg/mL and 1.0 μg/mL. Compared to the control group, there was no cytotoxic effect on the proliferation of the gingival fibroblasts.

CONCLUSION

In the present study, the oil of N. sativa was very active against MRSA and MRCoNS and had no in vitro cytotoxicity at relevant concentrations. These findings emphasize that there is a requirement for further clinical trials on N. sativa oil for "safe" medical management of infections caused by methicillin-resistant Staphylococci.

SUMMARY

The minimal inhibitory concentration (MIC) values of Nigella sativa oil against Staphylococcus aureus American Type Culture Collection (ATCC) 29213, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853 standard strains were 0.5 μg/mL, 2 μg/mL, 64 μg/mL, and 64 μg/mL, respectivelyThe N. sativa oil showed an excellent antibacterial activity against clinical isolates of methicillin-resistant S. aureus and methicillin-resistant coagulase-negative Staphylococci with very low MIC range of <0.25-1.0 µg/mLThe N. sativa oil exhibited no cytotoxic effect on the proliferation of the gingival fibroblasts. Abbreviation used: ATCC: American Type Culture Collection; CLSI: Clinical and Laboratory Standards Institute; CoNS: Coagulase-negative Staphylococci; DMEM: Dulbecco's modified Eagle's medium; DMSO: Dimethyl sulfoxide; FBS: Fetal bovine serum; HGF: Human gingival fibroblast; MIC: Minimal inhibitory concentration; MRCoNS: Methicillin-resistant CoNS; MRSA: Methicillin-resistant S. aureus.