In vitro activities of natural products against oral Candida isolates from denture wearers

Cryptocarya moschata extract decreases single and mixed biofilms on acrylic resins

OBJECTIVE

This study proposed to assess the effect of Cryptocarya moschata extract on single and mixed biofilms formed on denture base and reline acrylic resin.

MATERIALS AND METHODS

Single and mixed biofilms of Candida albicans and Streptococcus mutans were formed on the samples and treated with C. moschata extract; Nystatin solution at 100,000 IU/mL or Penicillin antibiotic solution at 100,000 IU/mL; or PBS solution. Antimicrobial activity was analyzed by counting colony-forming units, metabolism assay, assessment of protein components of the biofilm matrix, and of cell viability using confocal laser scanning microscopy (CLSM). Data were submitted to ANOVA and Tukey's post-test (α = 0.05).

RESULTS

Cryptocarya moschata extract reduced cell viability of C. albicans and S. mutans single and mixed biofilms formed on samples. For all types of biofilms in the C. moschata group, there was a log reduction of the biofilm, proven by the Alamar Blue assay. Analyzing the extracellular matrix protein components, groups treated with the extract exhibited a lower level of fluorescence compared to the PBS groups. Reduction in thickness biofilm and viable cells was perceptible in the C. moschata group when assessing through CLSM.

CONCLUSION

Cryptocarya moschata extract reduced the single and mixed biofilms of C. albicans and S. mutans on acrylic resins.

Improving Drug Delivery on Candida Albicans Using Geraniol Nanoemulsion

Geraniol (GE) is a monoterpene alcohol with excellent antifungal activity. However, its low solubility and high volatility impair its use. Nanoemulsions (NE) are excellent delivery systems for poorly soluble and volatile drugs, achieving controlled release of the active ingredient. The aim of this study was to improve the delivery of geraniol (GE) incorporated in NE against Candida albicans in order to evaluate the antibiofilm effect and cytotoxicity. Nanoemulsion containing 10% oil phase (cholesterol) (w/w), 10% surfactant (mixture of soy phosphatidylcholine and Brij 58; 1:2) (w/w), and 80% aqueous phase (phosphate buffer) (w/w) was synthesized. Incorporation of GE was carried out by sonication and the final compounds were characterized by hydrodynamic diameter, polydispersity index (PDI), and zeta potential (ZP), in addition to evaluation of physicochemical stability after 6 months and 1 year. The GE-NE effect was evaluated on Candida albicans biofilms and cytotoxic effect was evaluated on immortalized normal oral cell line NOK-Si. The diameter of GE-NE was 232.3 ± 2.7 nm and PDI 0.155 with exhibited homogeneity and stability in solution. GE-NE showed antibiofilm activity at a concentration of 75 μg/mL with reduction of >6.0 log10, and no cytotoxicity against NOK-Si cells at concentrations below 150 μg/mL was observed. GE-NE proved to be a promising candidate for prevention and treatment of fungal diseases.

A comparative evaluation of effect of denture cleansers on color stability, surface roughness and hardness of polyamide denture base material

CONTEXT

Different denture cleansers have an effect on color and different surface properties of polyamide denture base material. Thus, selecting a denture cleanser solution for polyamide denture base materials should be based on the properties of the denture cleanser itself. The present in vitro study is aimed to evaluate and compare the effect of different denture base cleansers on color, surface roughness and hardness of polyamide denture base material.

METHODS AND MATERIAL

Thirty specimens of commercially available polyamide denture base material were fabricated and divided into three groups of 10 each. Specimens from each group were immersed in different denture cleansers (sodium perborate, thyme oil and ozonated water) for 10 mins per day for 180 days. Initial and final color, surface roughness and surface hardness of each specimen were measured and the difference was calculated. Data was tabulated and subjected to statistical analysis using One way ANOVA for pair wise comparison.

RESULTS

Polyamide denture base resin exhibited some degree of change in color, surface roughness, and surface hardness in all denture cleansers but was not statistically significant.

CONCLUSIONS

The choice of denture cleanser for different denture base resins should be based on the chemistry of resin and the cleanser, denture cleanser concentration and duration of immersion.

Can Origanum be a hope for cancer treatment? A review on the potential of Origanum species in preventing and treating cancers

In this study, the potential of aromatic Origanum species belonging to Lamiaceae family to prevent and treat cancer was investigated. Since aromatic plants contain phytochemicals such as essential oils, phenolic acids, terpenoids, flavonoids, alkaloids, vitamins, enzymes and minerals with beneficial biological activities, they have become more interesting and important in medicine, pharmacy and industry. Publications/research between 1950 and 2022 were screened to investigate the effects of Origanum species on cancer, and the effects of their extracts and essential oils in cancer prevention and treatment. Essential phytochemicals found in plants provide efficacy in the prevention and treatment of many diseases. Besides, the essential oils found in these plant extracts are another reason that makes them important. Therefore, it is preferred in traditional medicine in the fight against many diseases as well as cancer. Essential oils of Origanum species mainly contain monoterpenes such as p-cymene, carvacrol, thymol and γ-terpinene. Since these compounds exhibit anticancer properties, Origanum species are becoming the plants of choice in the fight against cancer. In this context, Origanum majorana L. Origanum vulgare and Origanum munzurense are promising species, considering the composition of their extracts and essential oil.

In Vitro and In Vivo Activity of Citral in Combination with Amphotericin B, Anidulafungin and Fluconazole against Candida auris Isolates

Candida auris is an emerging fungal pathogen responsible for hospital outbreaks of invasive candidiasis associated with high mortality. The treatment of these mycoses is a clinical challenge due to the high resistance levels of this species to current antifungal drugs, and alternative therapeutic strategies are needed. In this study, we evaluated the in vitro and in vivo activities of combinations of citral with anidulafungin, amphotericin B or fluconazole against 19 C. auris isolates. The antifungal effect of citral was in most cases similar to the effect of the antifungal drugs in monotherapy. The best combination results were obtained with anidulafungin, with synergistic and additive interactions against 7 and 11 of the 19 isolates, respectively. The combination of 0.06 μg/mL anidulafungin and 64 μg/mL citral showed the best results, with a survival rate of 63.2% in Caenorhabditis elegans infected with C. auris UPV 17-279. The combination of fluconazole with citral reduced the MIC of fluconazole from > 64 to 1-4 μg/mL against 12 isolates, and a combination of 2 μg/mL fluconazole and 64 μg/mL citral was also effective in reducing mortality in C. elegans. Amphotericin B combined with citral, although effective in vitro, did not improve the activity of each compound in vivo.

Zerumbone Disturbs the Extracellular Matrix of Fluconazole-Resistant Candida albicans Biofilms

This study assessed the effect of zerumbone (ZER) against fluconazole-resistant (CaR) and -susceptible Candida albicans (CaS) biofilms and verified the influence of ZER on extracellular matrix components. Initially, to determine the treatment conditions, the minimum inhibitory concentration (MIC), the minimum fungicidal concentration (MFC) and the survival curve were evaluated. Biofilms were formed for 48 h and exposed to ZER at concentrations of 128 and 256 µg/mL for 5, 10 and 20 min (n = 12). One group of biofilms did not receive the treatment in order to monitor the effects. The biofilms were evaluated to determine the microbial population (CFU/mL), and the extracellular matrix components (water-soluble polysaccharides (WSP), alkali-soluble polysaccharides (ASPs), proteins and extracellular DNA (eDNA), as well as the biomass (total and insoluble) were quantified. The MIC value of ZER for CaS was 256 μg/mL, and for CaR, it was 64 μg/mL. The survival curve and the MFC value coincided for CaS (256 μg/mL) and CaR (128 μg/mL). ZER reduced the cellular viability by 38.51% for CaS and by 36.99% for CaR. ZER at 256 µg/mL also reduced the total biomass (57%), insoluble biomass (45%), WSP (65%), proteins (18%) and eDNA (78%) of CaS biofilms. In addition, a reduction in insoluble biomass (13%), proteins (18%), WSP (65%), ASP (10%) and eDNA (23%) was also observed in the CaR biofilms. ZER was effective against fluconazole-resistant and -susceptible C. albicans biofilms and disturbed the extracellular matrix.

Effect of Vapor-Phase Oregano Essential Oil on Resistant Candida Species Biofilms: Mechanisms of Action

Vulvovaginal candidiasis (VVC) is one of the most prevalent vaginal infectious diseases. The increasing incidence of drug-resistant Candida strains and the limited therapeutic options make the discovery of effective alternative therapies fundamental. Essential oils (EOs) have been suggested as a promising alternative, and interestingly, vapor-phase essential oils (VP-EOs) present more advantages than their direct application. Thus, this study aims to evaluate the effect of oregano VP-EO (VP-OEO) on biofilms of antifungal-resistant vaginal isolates of Candida species (Candida albicans and Candida glabrata) and determine its mode of action. CFU, membrane integrity, and metabolic activity were evaluated. Furthermore, a reconstituted vaginal epithelium was used to mimic vaginal conditions and evaluate the effect of VP-OEO on Candida species infection, analyzed by DNA quantification, microscopy, and lactate dehydrogenase activity. The results revealed high VP-OEO antifungal activity. There was a significant reduction (>4 log CFU) in Candida species biofilms. Furthermore, the results show that the mechanisms of action of VP-OEO are related to membrane integrity and metabolic activity. The epithelium model confirms the effectiveness of VP-OEO. This study suggests that VP-EO can be considered a first approach for the development of an alternative form of VVC treatment. IMPORTANCE This work presents a new approach to the application of essential oils, exposure to the vapor phase, which can be considered a first approach for the development of a complementary or alternative form of vulvovaginal candidiasis (VVC) treatment. VVC is a significant infection caused by Candida species and remains a common disease that affects millions of women every year. The great difficulty in treating VVC and the extremely limited effective therapeutic options make the development of alternative treatments crucial. In this scope, this study aims to contribute to the development of effective, inexpensive, and nontoxic strategies for the prevention and treatment of this infectious disease, based on natural products. Moreover, this new approach has several advantages for women, such as lower costs, easy access, an easier mode of application, avoidance of skin contact, and, therefore, fewer negative impacts on women's health.

Influence of menthol on biofilm formation, ergosterol content, and cell surface hydrophobicity of Candida glabrata

Resistance to synthetic antifungals has become one of the leading public health challenges around the world. Accordingly, novel antifungal products like naturally occurring molecules can be one of the potential ways to reach efficient curative approaches to control candidiasis. This work evaluated the effect of menthol on cell surface hydrophobicity (CSH), biofilm formation, growth, and ergosterol content of Candida glabrata, a yeast with a high resistance against antifungal agents. Disc diffusion method (susceptibility to synthetic antifungals), broth micro-dilution method (Susceptibility to menthol), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide reduction assay (biofilm formation), High-performance liquid chromatography (HPLC) technique (ergosterol content), and adherence to n-hexadecane (CSH) were employed to determine the influence of menthol against C. glabrata isolates. The minimum inhibitory concentration (MIC) range of menthol versus C. glabrata was 1250-5000 µg/mL (mean ± SD: 3375 ± 1375 µg/mL). The mean rate of C. glabrata biofilm formation was decreased up to 97.67%, 81.15%, 71.21%, 63.72%, 47.53%, 26.31%, and 0.051% at 625, 1250, 2500, 5000, 10 000, 20 000, and 40 000 µg/mL concentrations, respectively. The percentages of CSH were significant in groups treated with MIC/2 (17.51 ± 5.52%) and MIC/4 (26 ± 5.87%) concentrations of menthol. Also, the percentage changes in membrane ergosterol were 15.97%, 45.34%, and 73.40% at 0.125, 0.25, and 0.5 mg/mL concentrations of menthol, respectively, in comparison with untreated control. The results showed the menthol impact versus sessile and planktonic C. glabrata cells, and the interference with ergosterol content, CSH, and biofilm formation, which made it a potent natural antifungal.

Antibiotic properties of Satureja montana L. hydrolate in bacteria and fungus of clinical interest and its impact in non-target environmental microorganisms

The aim of this study was to analyse the microbicidal and microbiostatic activity of S. montana hydrolate L., the water-soluble fraction of the hydro-distillation process used to obtain the essential oil, on 14 Gram-positive and Gram-negative bacteria and a fungus of clinical interest. To consider whether this hydrolate is a more environmentally friendly alternative to traditional antibiotics, its effect on non-target microorganisms in the aquatic and terrestrial environment was analysed using natural soil and river microorganism communities, characterized through 16S rRNA gene sequencing. Results showed that S. montana hydrolate was especially effective (25% v/v concentration) against Pasteurella aerogenes, Streptococcus agalactiae and Acinetobacter baumannii (priority 1, WHO). It was also a microbicide for a further 7 bacterial strains and the fungus Candida albicans (50% v/v concentration). The river and soil communities exposed to the hydrolate showed a decrease in their growth, as well as a decrease in their ability to metabolize polymers and carbohydrates (soil microorganisms) and polymers, carboxylic and ketone acids (river microorganisms). Hydrolates could be an alternative to conventional antibiotics, but their impact on the environment must be taken into account.

Autotoxicity of Endogenous Organic Acid Stress in Two Ganoderma lucidum Cultivars

Ganoderma lucidum has been used as a rare medical mushroom for centuries in China, due to its health-promoting properties. Successive cropping obstacles are common in the cultivation of G. lucidum, although the remaining nutrients in the germ substrate are sufficient for a second fruiting. Here, we aimed to study the metabolite profile of G. lucidum via nontargeted metabonomic technology. Metabonomic data revealed that organic acids played an important role in the cropping obstacles of G. lucidum, which is accordance with the pH decrease in the germ substrate. A Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis indicated that most differential acids participated in the metabolic pathways. Five acids were all significantly upregulated by two MS with high energy (MSE) modes in two cultivars, among which 5-hydroxy-2-oxo-4-ureido-2,5-dihydro-1H-imidazole-5-carboxylic acid is also involved in purine metabolism regulation and microbial metabolism in diverse environments. Taken together, this work illustrated the organic acid stress generated by G. lucidum, which formed the autotoxicity feedback, and resulted in cropping obstacles. Determining the cause of the cropping obstacles in G. lucidum will promote the utilization rate of fungus substrate to realize the sustainable use of this resource.

Antifungal Activity of Lavandula angustifolia Essential Oil against Candida albicans: Time-Kill Study on Pediatric Sputum Isolates

The aim of our study was to determine the susceptibility of 15 Candida albicans sputum isolates on fluconazole and caspofungin, as well as the antifungal potential of Lavandula angustifolia essential oil (LAEO). The commercial LAEO was analyzed using gas chromatography-mass spectrometry. The antifungal activity was evaluated using EUCAST protocol. A killing assay was performed to evaluate kinetics of 2% LAEO within 30 min treatment. LAEO with major constituents’ linalool (33.4%) and linalyl acetate (30.5%) effective inhibited grows of C. albicans in concentration range 0.5–2%. Fluconazole activity was noted in 67% of the isolates with MICs in range 0.06–1 µg/mL. Surprisingly, 40% of isolates were non-wild-type (non-WT), while MICs for WT ranged between 0.125–0.25 µg/mL. There were no significant differences in the LAEO MICs among fluconazole-resistant and fluconazole-susceptible sputum strains (p = 0.31) and neither among caspofungin non-WT and WT isolates (p = 0.79). The 2% LAEO rapidly achieved 50% growth reduction in all tested strains between 0.2 and 3.5 min. Within 30 min, the same LAEO concentration exhibited a 99.9% reduction in 27% isolates. This study demonstrated that 2% solution of LAEO showed a significant antifungal activity which is equally effective against fluconazole and caspofungin susceptible and less-susceptible strains.

Eugenol: A novel therapeutic agent for the inhibition of Candida species infection

The high occurrence and mortality rates related to candidiasis emphasize the urgent need to introduce new therapeutic approaches to treat this infection. Eugenol, the main phenolic component of Clove and Cinnamomum essential oil, has been used to inhibit growth and different virulence factors of Candida, including strains with decreased susceptibility to antifungals, particularly fluconazole. The results showed that this compound could bind to Candida membrane and decrease ergosterol biosynthesis, consequently leading to cell wall and membrane damage. Additionally, eugenol not only reduced germ tube formation, which reduces nutrient absorption from host tissues, but it also increased the levels of lipid peroxidation and reactive oxygen species, which induces oxidative stress and causes high permeability in the fungal cell membrane. Eugenol inhibited Candida cells’ adhesion capacity; additionally, this compound inhibited the formation of biofilms and eliminated established Candida biofilms on a variety of surfaces. Furthermore, by disrupting fungal cell integrity, eugenol could boost the entry of the antifungal drugs into the Candida cell, improving treatment efficacy. Therefore, eugenol could be used in the clinical management of various presentations of candidiasis, especially mucocutaneous presentations such as oral and vulvovaginal infections. However, further investigations, including in vivo and animal studies, toxicology studies and clinical trials, as well as molecular analysis, are needed to improve formulations and develop novel antifungal agents based on eugenol.

Potential Applications of Essential Oils for Environmental Sanitization and Antimicrobial Treatment of Intensive Livestock Infections

The extensive use of antibiotics has contributed to the current antibiotic resistance crisis. Livestock infections of Salmonella spp, Clostridium spp. and E. coli antimicrobial-resistant bacteria represent a public threat to human and animal health. To reduce the incidence of these zoonoses, essential oils (EOs) could be effective antibiotic alternatives. This study aims at identifying EOs safe for use, effective both in complementary therapy and in the environmental sanitization of intensive farming. Natural products were chemo-characterized by gas chromatography. Three S. Typhimurium, three C. perfringens and four E. coli strains isolated from poultry and swine farms were used to assess the antimicrobial properties of nine EOs and a modified GR-OLI (mGR-OLI). The toxicity of the most effective ones (Cinnamomum zeylanicum, Cz; Origanum vulgare, Ov) was also evaluated on porcine spermatozoa and Galleria mellonella larvae. Cz, Ov and mGR-OLI showed the strongest antimicrobial activity; their volatile components were also able to significantly inhibit the growth of tested strains. In vitro, Ov toxicity was slightly lower than Cz, while it showed no toxicity on G. mellonella larvae. In conclusion, the study confirms the importance of evaluating natural products to consolidate the idea of safe EO applications in reducing and preventing intensive livestock infections.

Gas Chromatography-Mass Spectrometry Analysis and Inhibitory Activity Against Candida albicans ATCC 10231 of the Leave Ethanolic Extract From Citrus aurantifolia (Christm.) Swingle

Background: Candida albicans is one of the important infectious yeasts that is associated with candidiasis, including oral candidiasis. The extracts of various herbal materials are potential for treating candidiasis. Objectives: The objectives of this study were to determine phytochemical constituents of the leaf ethanolic extract of Citrus aurantifolia with gas chromatography-mass spectrometry (GC-MS) and to investigate the inhibiting effect of this extract on the planktonic growth of C. albicans. Methods: The fresh leaves of C. aurantifolia were macerated overnight with ethanol. The extract was analysed with GC-MS. C. albicans ATCC 10231 was used in this study. The well-diffusion procedure was applied to detect the anti-candida activity qualitatively. Finally, real-time planktonic growth was employed for detecting the anti-candida activity quantitatively. Results: GC-MS analysis revealed four dominant components in the ethanolic leaf extract of C. aurantifolia, namely, limonene, geraniol, phytol, and caryophyllene. The extract inhibited the growth of C. albicans either under the agar diffusion test or real-time planktonic growth. The specific growth rate of C. albicans was slower in the liquid culture with the extract. The specific growth rates of the 0 (control), 13.3, and 26.6 µg/mL were 0.582, 0.384, and 0.272, respectively. Eventually, the yields of the treated growth with 0 (control), 13.3, and 26.6 µg/mL were OD850 of 4.5, 3.0, and 3.7, respectively. Conclusion: The leaf ethanolic extract of C. aurantifolia contains bioactive compounds which have anticandida activity. Thus, it is a good material for new anti-candida ingredients in the future

Antifungal Activity and Acute and Repeated-Dose Toxicity Study of Geranyl Cinnamate Ester in Mice

In the present study, the antifungal activity and toxicity of the geranyl cinnamate ester (GCE) were investigated. The GCE showed antifungal activity at a minimum concentration of 0.16 μL/mL against Candida albicans and at concentrations greater than 2.5 μL/mL against Aspergillus niger. In acute toxicity studies, the administration of GCE (2.000 mg/kg) affected the body weight gain and food intake but did not induce the mortality of the animals studied. After the investigation of repeated-dose toxicity of GCE at 2 and 4 mg/kg, the hematological and biochemical parameters were changed. In addition, the adrenal weight of male mice treated with GCE at 4 mg/kg was affected. In conclusion, according to the Organization for Economic Cooperation and Development (OECD) acute toxicity parameters, the geranyl cinnamate ester can be classified into safety category number 5. The results of this study suggested that the geranyl cinnamate ester may be a source of natural antifungals.

In vitro activities of carvacrol, cinnamaldehyde and thymol against Candida biofilms

Oral candidiasis is frequently associated with Candida biofilms. Biofilms are microbial communities related to persistent, recalcitrant and difficult to-treat infections. Conventional treatments are not sufficient to overcome biofilm-associated candidiasis; thus, the search of new antifungal compounds is necessary. In the current study, we have evaluated the effect of three phytocompounds, carvacrol, cinnamaldehyde and thymol, against Candida planktonic and sessile cells. Reduction in biofilm biomass and metabolic activity was assessed during adhesion and mature biofilm phases. Candida albicans was the most biofilm-producing Candida species. All phytocompounds tested were fungicidal against Candida planktonic cells. Cinnamaldehyde was the most active in inhibiting biofilm adhesion, but carvacrol and thymol significantly reduced both mature biofilm biomass and metabolic activity. These results highlight the role of cinnamaldehyde, carvacrol and thymol as promising alternatives for the treatment of candidiasis due to their antibiofilm capacities, and stress the necessity to continue studies on their safety, toxicity and pharmacodynamics and pharmacokinetics.

Update on Candida krusei, a potential multidrug-resistant pathogen

Although Candida albicans remains the main cause of candidiasis, in recent years a significant number of infections has been attributed to non-albicans Candida (NAC) species, including Candida krusei. This epidemiological change can be partly explained by the increased resistance of NAC species to antifungal drugs. C. krusei is a diploid, dimorphic ascomycetous yeast that inhabits the mucosal membrane of healthy individuals. However, this yeast can cause life-threatening infections in immunocompromised patients, with hematologic malignancy patients and those using prolonged azole prophylaxis being at higher risk. Fungal infections are usually treated with five major classes of antifungal agents which include azoles, echinocandins, polyenes, allylamines, and nucleoside analogues. Fluconazole, an azole, is the most commonly used antifungal drug due to its low host toxicity, high water solubility, and high bioavailability. However, C. krusei possesses intrinsic resistance to this drug while also rapidly developing acquired resistance to other antifungal drugs. The mechanisms of antifungal resistance of this yeast involve the alteration and overexpression of drug target, reduction in intracellular drug concentration and development of a bypass pathway. Antifungal resistance menace coupled with the paucity of the antifungal arsenal as well as challenges involved in antifungal drug development, partly due to the eukaryotic nature of both fungi and humans, have left researchers to exploit alternative therapies. Here we briefly review our current knowledge of the biology, pathophysiology and epidemiology of a potential multidrug-resistant fungal pathogen, C. krusei, while also discussing the mechanisms of drug resistance of Candida species and alternative therapeutic approaches.

Essential oils as Potential Source of Anti-dandruff Agents: A Review

BACKGROUND

Dandruff is a frequently occurring scalp problem that causes significant discomfort to approximately 50% population at some stage of life, especially post-puberty and pre-adult age.

OBJECTIVE

This review aims to summarize the recent findings regarding the anti-fungal properties of herbal essential oils against pathogens involved in dandruff prognosis.

METHODS

A literature search of studies published between 2000 and 2020 was conducted over databases: PubMed, Google Scholar, Scopus, and Science direct. Literature was explored using the guidelines given in Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

RESULTS

Dandruff, characterized by clinical symptoms of dryness, pruritis, scaly, and flaky scalp, is considered a pri-mary manifestation of seborrheic dermatitis. Amongst various etiological and pathophysiological factors, a significant role of yeasts, primarily species of Malassezia, Candida, has been strongly correlated with dandruff. At the same time, incidences of M. furfur, M. restricta, and M. globosa are high compared to others. Due to relapse of symptoms with the withdrawal of conventional anti-dandruff products. Essential oils of herbal origin, such as tea tree oil, lime oil, rose-mary oil, have gained global importance in dermatology. These oils are rich in secondary aromatic metabolites, espe-cially terpenes and phenolic components that impart substantial antimicrobial properties and resisting biofilm production.

CONCLUSION

Based on the available information, we can conclude that essential oils have tremendous potential to be developed as anti-dandruff products; however, further studies are warranted to establish their efficacy in dandruff cures.

The in-vitro effects of white henna addition on the Candida albicans adhesion and physical properties of denture base resin

Purpose:

This in-vitro study evaluated and compared the effect of white henna (WH) and natural henna (NH) addition on Candida albicans adhesion and physical properties of the denture base material.

Materials and methods:

A total of 243 acrylic resin specimens (9 per group) were divided as follows: 81 for flexural strength, 81 for Candida albicans adherence test, and 81 for surface roughness, translucency, and hardness. Heat-polymerized acrylic resin specimens were prepared by adding 0.5, 1.0, 1.5, or 2.0 wt% of WH or NH. Candida albicans adhesion was determined using direct culture and slide count methods. Flexural strength, surface roughness, hardness, and translucency were measured using the three-point bending test, profilometer, Vickers hardness test, and spectrophotometer, respectively. ANOVA and post hoc Tukey’s tests were performed for data analysis.

Results:

Addition of 0.5% WH, 1% WH, and 0.5% NH to denture base resin significantly decreased Candida albicans adhesion (p<0.05). WH and NH significantly decreased the flexural strength and translucency, except 0.5% WH, and significantly increased surface roughness, except 0.5% WH and 0.5% NH. WH addition showed nonsignificant differences in the hardness, while NH addition significantly decreased hardness (p<0.05).

Conclusion:

Addition of WH and NH decreased C. albicans adhesion to PMMA denture base resin. However, flexural strength, translucency, and surface roughness were adversely affected, particularly at higher concentrations. Hardness was reduced with NH only.

Mechanistic Understanding of Candida albicans Biofilm Formation and Approaches for Its Inhibition

In recent years, the demand for novel antifungal therapies has increased several- folds due to its potential to treat severe biofilm-associated infections. Biofilms are made by the sessile microorganisms attached to the abiotic or biotic surfaces, enclosed in a matrix of exopolymeric substances. This results in new phenotypic characteristics and intrinsic resistance from both host immune response and antimicrobial drugs. Candida albicans biofilm is a complex association of hyphal cells that are associated with both abiotic and animal tissues. It is an invasive fungal infection and acts as an important virulent factor. The challenges linked with biofilm-associated diseases have urged scientists to uncover the factors responsible for the formation and maturation of biofilm. Several strategies have been developed that could be adopted to eradicate biofilm-associated infections. This article presents an overview of the role of C. albicans biofilm in its pathogenicity, challenges it poses and threats associated with its formation. Further, it discusses strategies that are currently available or under development targeting prostaglandins, quorum-sensing, changing surface properties of biomedical devices, natural scaffolds, and small molecule-based chemical approaches to combat the threat of C. albicans biofilm. This review also highlights the recent developments in finding ways to increase the penetration of drugs into the extracellular matrix of biofilm using different nanomaterials against C. albicans.

Antifungal Efficacy and Physical Properties of Poly(methylmethacrylate) Denture Base Material Reinforced with SiO2 Nanoparticles

PURPOSE

To evaluate the effect of the addition of low concentration of silicon-dioxide nanoparticles (nano-SiO₂ ) to poly(methylmethacrylate) (PMMA) denture base material on Candida albicans adhesion, surface roughness, contact angle, hardness, and translucency.

MATERIALS AND METHODS

A total of 150 acrylic disks were fabricated from heat-polymerized acrylic resin and specimens were divided into 3 groups of 50 per test. They were further subdivided into 5 subgroups (n = 10) according to the concentration of nano-SiO₂ : control (no addition) and four tested groups modified with 0.05, 0.25, 0.5, and 1.0 wt% nano-SiO₂ of acrylic powder. Slide count and direct culture methods were used to measure C. albicans count (CFU/mL). The surface roughness values (R_a ; μm) were determined using a profilometer. The contact angle (^o ) measurement was performed by a goniometer using the sessile drop method. Vickers hardness was used to analyze surface hardness. Translucency was measured using a spectrophotometer. Data analysis was conducted through analysis of variance and Tukey's post hoc tests (α = 0.05).

RESULTS

Compared to the control group, direct culture and slide count methods illustrated a significant decrease in C. albicans count (p ˂ 0.001) with the addition of nano-SiO₂ , and this decrease was correlated with the concentration of nano-SiO₂ . The addition of nano-SiO₂ significantly decreased the contact angle (p ˂ 0.001), whereas hardness and surface roughness significantly increased (p ˂ 0.001). The addition of nano-SiO₂ significantly decreased translucency (p ˂ 0.001), and this decrease was concentration dependent.

CONCLUSION

Addition of low concentration of nano-SiO₂ decreased C. albicans adhesion to PMMA denture base resin. Also, low additions of nano-SiO₂ have positive effects on contact angle and hardness, whereas surface roughness and translucency were adversely affected at high concentrations.

Role of symbiosis in the discovery of novel antibiotics

Antibiotic resistance has been an ongoing challenge that has emerged almost immediately after the initial discovery of antibiotics and requires the development of innovative new antibiotics and antibiotic combinations that can effectively mitigate the development of resistance. More than 35,000 people die each year from antibiotic resistant infections in just the United States. This signifies the importance of identifying other alternatives to antibiotics for which resistance has developed. Virtually, all currently used antibiotics can trace their genesis to soil derived bacteria and fungi. The bacteria and fungi involved in symbiosis is an area that still remains widely unexplored for the discovery and development of new antibiotics. This brief review focuses on the challenges and opportunities in the application of symbiotic microbes and also provides an interesting platform that links natural product chemistry with evolutionary biology and ecology.

Terpinen-4-ol inhibits the growth of Sporothrix schenckii complex and exhibits synergism with antifungal agents

Aim: This study investigated the effect of terpinen-4-ol against Sporothrix schenckii complex and its interactions with antifungals. Materials & methods: The antifungal activity of terpinen-4-ol was evaluated by broth microdilution. The potential effect on cellular ergosterol concentration was evaluated by spectrophotometry. The antibiofilm activity was evaluated by violet crystal staining and XTT reduction assay. The potential pharmacological interactions with antifungals were evaluated by the checkerboard assay. Results: terpinen-4-ol (T-OH) showed minimal inhibitory concentrations ranging from 4 to 32 mg/l decreasing cellular ergosterol content and presented a SMIC ranging from 64 to 1024 mg/l for Sporothrix spp. The combinations of T-OH with itraconazole or terbinafine were synergistic. Conclusion: T-OH has antifungal activity against Sporothrix spp. and acts synergistically with standard antifungals.

In vitro synergy of eugenol on the antifungal effects of voriconazole against Candida tropicalis and Candida krusei strains isolated from the genital tract of mares

BACKGROUND

Due to the limited range of antifungals available to treat genital Candida infections and the emergence of resistant isolates, attention has focused on the antifungal potency of natural compounds with promising biological properties.

OBJECTIVES

To examine whether eugenol synergises the in vitro efficacy of voriconazole against Candida strains isolated from the genital tract of mares.

STUDY DESIGN

In vitro experiment.

METHODS

The antifungal activity of eugenol and voriconazole was evaluated using the broth microdilution assay (CLSI- M27-A3). Synergism of eugenol and voriconazole against genital Candida isolates was evaluated by the microdilution checkerboard method.

RESULTS

Minimum inhibitory concentration (MIC) values for eugenol and voriconazole ranged from 400 to 800 µg/mL and 1 to 8 µg/mL, respectively, for C. tropicalis isolates, and from 200 to 400 µg/mL for eugenol and 2 to 16 µg/mL for voriconazole against C. krusei isolates. Eugenol decreased the arithmetic mean MIC for voriconazole against C. tropicalis and C. krusei isolates from 2.66 to 0.46 µg/mL and 7.77 to 0.41 µg/mL respectively. The fractional inhibitory concentration index (FICI) values for the eugenol-voriconazole combination ranged from 0.25 to 0.88 and 0.19 to 0.63 for C. tropicalis and C. krusei isolates respectively. A synergistic effect of eugenol in combination with voriconazole was observed for 83.3% of C. tropicalis and 77.7% of C. krusei isolates. Antagonistic activity was not seen in any of the isolates tested.

MAIN LIMITATIONS

Since in vitro antifungal susceptibility tests are not systematic analyses, any selection bias could influence the results. In addition, in vitro susceptibility does not uniformly predict clinical success in vivo.

CONCLUSIONS

Eugenol showed fungistatic and fungicidal effects against genital Candida isolates and, in combination, synergised the antifungal effects of voriconazole. The eugenol-voriconazole combination can lay the foundation for a therapeutic approach against isolates in which azole resistance has increased over time.

Optimum Inhibition of Amphotericin-B-Resistant Candida albicans Strain in Single- and Mixed-Species Biofilms by Candida and Non-Candida Terpenoids

Candida albicans is one of the most common human fungal pathogens and represents the most important cause of opportunistic mycoses worldwide. Surgical devices including catheters are easily contaminated with C. albicans via its formation of drug-resistant biofilms. In this study, amphotericin-B-resistant C. albicans strains were isolated from surgical devices at an intensive care center. The objective of this study was to develop optimized effective inhibitory treatment of resistant C. albicans by terpenoids, known to be produced naturally as protective signals. Endogenously produced farnesol by C. albicans yeast and plant terpenoids, carvacrol, and cuminaldehyde were tested separately or in combination on amphotericin-B-resistant C. albicans in either single- or mixed-infections. The results showed that farnesol did not inhibit hyphae formation when associated with bacteria. Carvacrol and cuminaldehyde showed variable inhibitory effects on C. albicans yeast compared to hyphae formation. A combination of farnesol with carvacrol showed synergistic inhibitory activities not only on C. albicans yeast and hyphae, but also on biofilms formed from single- and mixed-species and at reduced doses. The combined terpenoids also showed biofilm-penetration capability. The aforementioned terpenoid combination will not only be useful in the treatment of different resistant Candida forms, but also in the safe prevention of biofilm formation.

Antimicrobial activity of eugenol against carbapenem-resistant Klebsiella pneumoniae and its effect on biofilms

A preliminary study found that eugenol expressed an antibacterial activity against Klebsiella pneumoniae. However, the mechanism of action of eugenol against K. pneumoniae still remains unexplored. The aim of this study was to gain further insight into the antibacterial effect of eugenol against carbapenem-resistant Klebsiella pneumoniae (CRKP) and possible mode of action. Here, minimum inhibitory concentration (MIC) of eugenol against CRKP strains was determined using the agar dilution method. Moreover, variations in intracellular ATP concentration, intracellular pH (pH_in), membrane potential and membrane integrity were measured to evaluate the effect of eugenol on cell membrane. Besides, changes in cell structure and biofilm formation of CRKP as well as biofilm-associated cell damage were determined using field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and confocal laser scanning microscopy (CLSM). Finally, gene expression of biofilm-related biosynthesis was investigated. The results showed that MICs of eugenol against four tested CRKP were 0.2 mg/mL. Eugenol damaged the cell membrane of CRKP, as evidenced by decreased intracellular ATP concentration, reduced pH_in and cell membrane hyperpolarization, coupled with enhanced membrane permeability. Furthermore, eugenol compromised cell structure and induced loss of intracellular components of CRKP. Additionally, eugenol inhibited biofilm formation and inactivated biofilm CRKP cells. Finally, eugenol presented strong inhibitory effects on biofilm formation and biofilm-associated gene expression, and inactivated CRKP cells growing in biofilms. These findings suggest that eugenol exhibits antimicrobial effect against CRKP strains and could be potentially used to control CRKP-related infections.

Exploration of Medicinal Plants as Sources of Novel Anticandidal Drugs

BACKGROUND

Human infections associated with skin and mucosal surfaces, mainly in tropical and sub-tropical parts of the world. During the last decade, there have been an increasing numbers of cases of fungal infections in immunocompromised patients, coupled with an increase in the number of incidences of drug resistance and toxicity to anti fungal agents. Hence, there is a dire need for safe, potent and affordable new antifungal drugs for the efficient management of candidal infections with minimum or no side effects.

INTRODUCTION

Candidiasis represents a critical problem to human health and a serious concern worldwide. Due to the development of drug resistance, there is a need for new antifungal agents. Therefore, we reviewed the different medicinal plants as sources of novel anticandidal drugs.

METHODS

The comprehensive and detailed literature on medicinal plants was carried out using different databases, such as Google Scholar, PubMed, and Science Direct and all the relevant information from the articles were analyzed and included.

RESULTS

Relevant Publications up to the end of November 2018, reporting anticandidal activity of medicinal plants has been included in the present review. In the present study, we have reviewed in the light of SAR and mechanisms of action of those plants whose extracts or phytomolecules are active against candida strains.

CONCLUSION

This article reviewed natural anticandidal drugs of plant origin and also summarized the potent antifungal bioactivity against fungal strains. Besides, mechanism of action of these potent active plant molecules was also explored for a comparative study. We concluded that the studied active plant molecules exhibit potential antifungal activity against resistant fungal strains.

Therapeutic tools for oral candidiasis: Current and new antifungal drugs

BACKGROUND

Candidiasis is one of the most common opportunistic oral infections that presents different acute and chronic clinical presentations with diverse diagnostic and therapeutic approaches. The present study carries out a bibliographic review on the therapeutic tools available against oral candidiasis and their usefulness in each clinical situation.

MATERIAL AND METHODS

Recent studies on treatment of oral candidiasis were retrieved from PubMed and Cochrane Library.

RESULTS

Nystatin and miconazole are the most commonly used topical antifungal drugs. Both antifungal drugs are very effective but need a long time of use to eradicate the infection. The pharmacological presentations of miconazole are more comfortable for patients but this drug may interact with other drugs and this fact should be assessed before use. Other topical alternatives for oral candidiasis, such as amphotericin B or clotrimazole, are not available in many countries. Oral fluconazole is effective in treating oral candidiasis that does not respond to topical treatment. Other systemic treatment alternatives, oral or intravenous, less used are itraconazole, voriconazole or posaconazole. Available novelties include echinocandins (anidulafungin, caspofungin) and isavuconazole. Echinocandins can only be used intravenously. Isavuconazole is available for oral and intravenous use. Other hopeful alternatives are new drugs, such as ibrexafungerp, or the use of antibodies, cytokines and antimicrobial peptides.

CONCLUSIONS

Nystatin, miconazole, and fluconazole are very effective for treating oral candidiasis. There are systemic alternatives for treating recalcitrant infections, such as the new triazoles, echinocandins, or lipidic presentations of amphotericin B.

Geraniol and linalool anticandidal activity, genotoxic potential and embryotoxic effect on zebrafish

Aim: Geraniol and linalool are major constituents of the essential oils of medicinal plants. Materials & methods: Antifungal activity of geraniol and linalool were evaluated against five Candida species. The genotoxicity of these compounds was evaluated by the cytokinesis-block micronucleus test, and the embryotoxic assays use zebrafish model. Results: Geraniol and linalool inhibited Candida growth, but geraniol was more effective. The geraniol at concentration of 800 μg/ml and the linalool at concentration of 125 μg/ml significantly increased chromosome damage. Geraniol was more toxic to zebrafish embryo than linalool: LC50 values were 31.3 and 193.3 μg/ml, respectively. Conclusion: Geraniol and linalool have anticandidal activity, but they also exert genotoxic and embryotoxic effects at the highest tested concentrations.

Quercus Brantii Lindl. Vaginal Douche Versus Clotrimazole on Vaginal Candidiasis: A Randomized Clinical Trial

Objectives

Vaginal Candidiasis with an approximate prevalence of 30% is the second cause of vaginal infections. Antifungal azole is the first treatment for Vaginal Candidiasis; however, some side effects have been reported for this chemical medicine. Based on the antifungal activity of Inner Stratum of Quercus Brantii (Q. Brantii), the aim of our study was to compare the effects of vaginal douche of Q. Brantii extract and clotrimazole on vaginal candidiasis symptoms before and after the treatments, in women.

Methods

89 non-pregnant women with positive KOH test which is capable of identifying the presence of hyphae and mycelium by adding KOH (10%), and a positive vaginal candidiasis culture were randomly divided into two experimental groups, using permuted block randomization method. One group received clotrimazole vaginal cream (1%) and the other group received vaginal douche of Q. Brantii extract. Groups were treated for 7 days and KOH tests and cultures were evaluated again. Data were analyzed via chi-square and independent t-test, using SPSS software.

Results

According to the results, there were no significant differences between experimental groups for demographic characteristics like age (p=0.403), BMI (p=0.911), educational levels (p=0.862) and contraceptive methods (p=0.702). Moreover, significant differences were seen in vaginal discharge between the groups after the treatments (P=0.043).

Conclusion

The results suggested that the therapeutic effect of vaginal douche of Q. Brantii extract was approximately similar to that of clotrimazole vaginal cream.

Properties of an acrylic resin after immersion in antiseptic soaps: Low-cost, easy-access procedure for the prevention of denture stomatitis

Denture stomatitis triggered by Candida species requires better preventive measures. This study evaluated the physical and biological properties of a denture base acrylic resin after immersion in antiseptic soaps. Acrylic resin specimens were prepared and stored in distinct solutions for 0, 7, 14, 21, and 28 days. The solutions were as follows: DW: distilled water at 37°C (control group); DS: cycles of daily immersion in Dettol soap for 8 hours at room temperature, followed by immersion in distilled water for 16 hours at 37°C; PS: cycles of daily immersion in Protex soap, as described for the previous group; LS: cycles of daily immersion in Lifebuoy soap, as described for the DS group. The parameters evaluated at each time point were the following: biofilm formation capacity by Candida albicans and reduction of preformed fungal biofilms, cytotoxicity, surface roughness, hardness, and color change. For the fungal adhesion phase, the type of soap had a statistically significant effect (p = 0.0292), but after 24 hours, no differences were found between solutions or between storage times. Regarding the efficacy of biofilm reduction, there was a significant difference when the groups were compared to each other (p = 0.014). Dettol and Lifebuoy eliminated the preformed biofilm on the specimens. Moreover, all the soaps were classified as non-cytotoxic (on HaCaT cell line) because there was no difference in cell viability between the different groups, except after 21 days, when a decrease in cell viability occurred, regardless of the type of soap. Regarding the roughness, there was no statistically significant difference (p > 0.05) between the groups. Lifebuoy decreased resin hardness regardless of storage time (p = 0.003). After 21 and 28 days of storage, there was an increase in hardness value, regardless of the type of soap. The specimens’ color, according to the National Bureau of Standards values, ranged from 0.27 to 0.58 (i.e., imperceptible or mild color changes). In general, the disinfectant soaps were not able to prevent biofilm formation, but all the soaps were effective in reducing the preformed biofilm. In addition, all soaps were non-cytotoxic and did not change surface roughness, hardness (except Lifebuoy), and color (except Lifebuoy). Therefore, immersion in two antiseptic soaps (Protex and Dettol) may be a cheap and easy procedure for preventing denture stomatitis.

The natural plant compound carvacrol as an antimicrobial and anti-biofilm agent: mechanisms, synergies and bio-inspired anti-infective materials

Carvacrol (5-isopropyl-2-methyl phenol) is a natural compound that occurs in the leaves of a number of plants and herbs including wild bergamot, thyme and pepperwort, but which is most abundant in oregano. The aim of this review is to analyse the scientific data from the last five years (2012-2017) on the antimicrobial and anti-biofilm activities of carvacrol, targeting different bacteria and fungi responsible for human infectious diseases. The antimicrobial and anti-biofilm mechanisms of carvacrol and its synergies with antibiotics are illustrated. The potential of carvacrol-loaded anti-infective nanomaterials is underlined. Carvacrol shows excellent antimicrobial and anti-biofilm activities, and is a very interesting bioactive compound against fungi and a wide range of Gram-positive and Gram-negative bacteria, and being active against both planktonic and sessile human pathogens. Moreover, carvacrol lends itself to being combined with nanomaterials, thus providing an opportunity for preventing biofilm-associated infections by new bio-inspired, anti-infective materials.

Antifungal Activity of Commercial Essential Oils and Biocides against Candida Albicans

Management of oral candidosis, most frequently caused by Candida albicans, is limited due to the relatively low number of antifungal drugs and the emergence of antifungal tolerance. In this study, the antifungal activity of a range of commercial essential oils, two terpenes, chlorhexidine and triclosan was evaluated against C. albicans in planktonic and biofilm form. In addition, cytotoxicity of the most promising compounds was assessed using murine fibroblasts and expressed as half maximal inhibitory concentrations (IC50). Antifungal activity was determined using a broth microdilution assay. The minimum inhibitory concentration (MIC) was established against planktonic cells cultured in a range of concentrations of the test agents. The minimal biofilm eradication concentration (MBEC) was determined by measuring re-growth of cells after pre-formed biofilm was treated for 24 h with the test agents. All tested commercial essential oils demonstrated anticandidal activity (MICs from 0.06% (v/v) to 0.4% (v/v)) against planktonic cultures, with a noticeable increase in resistance exhibited by biofilms (MBECs > 1.5% (v/v)). The IC50s of the commercial essential oils were lower than the MICs, while a one hour application of chlorhexidine was not cytotoxic at concentrations lower than the MIC. In conclusion, the tested commercial essential oils exhibit potential as therapeutic agents against C. albicans, although host cell cytotoxicity is a consideration when developing these new treatments.

Characterization of Herbal Antifungal Agent, Origanum vulgare against Oral Candida spp. Isolated from Patients with Candida-Associated Denture Stomatitis: An In vitro Study

Background:

Candida Associated Denture Stomatitis is the prevalent fungal pathosis in denture wearers, especially in immunocompromized patients. Existing antifungal agents are ineffective since the Candida species become resistant and also, they become toxic. Origanum vulgare is a herbal plant with high anti-fungal activity against Candida of blood and urine origin. However, it has never been explored against Candida from oral cavity.

Materials & Methodology:

Dry leaves of the plant were purchased and authenticated. Oil extraction was done using Hydro-distillation method. Clinical isolates of Candida from denture wearers was speciated using CHROMagar. Well Diffusion test was used to confirm the antifungal activity. Hydro-distillation & Maceration methods of extraction were compared. MIC/MFC was determined using CSLI guidelines. Infra-Red Spectroscopy was used to identify the active functional group.

Results:

O.vulgare showed 30±3mm of zone of inhibition as against 19mm for fluconazole. The suitable extraction method was Hydro-distillation. MIC & MFC were found to be 0.024% and 0.097% respectively which was much lesser than for fluconazole (0.25%). The active functional group had chemically similar structure as Carvacrol, usually found in antifungal herbs.

Conclusion:

within the limitations of the study, it was concluded that (a)O.vulgare is anticandidal for clinical isolates of oral Candida, (b) Hydro-distillation is an effective method as compared to Maceration (c) MIC & MFC are much lower than that of fluconazole (d) the major functional group was structurally similar to Carvacrol.

Antifungal Compounds against Candida Infections from Traditional Chinese Medicine

Infections caused by Candida albicans, often refractory and with high morbidity and mortality, cause a heavy burden on the public health while the current antifungal drugs are limited and are associated with toxicity and resistance. Many plant-derived molecules including compounds isolated from traditional Chinese medicine (TCM) are reported to have antifungal activity through different targets such as cell membrane, cell wall, mitochondria, and virulence factors. Here, we review the recent progress in the anti-Candida compounds from TCM, as well as their antifungal mechanisms. Considering the diverse targets and structures, compounds from TCM might be a potential library for antifungal drug development.

Denture Stomatitis: Causes, Cures and Prevention

Removable dentures are worn by 20% of the UK population and two thirds of these individuals have denture stomatitis. Poor oral hygiene is commonplace among this group, as is smoking and xerostomia, which also contribute to the development of denture stomatitis. A complex polymicrobial biofilm is able to proliferate on the surface of denture materials and matures to form visible denture plaque. This denture plaque biofilm stimulates a local inflammatory process that is detectable clinically as erythema, and hyperplasia. Systemically, denture plaque represents a potential risk factor for systemic disease, in particular aspiration pneumonia. Respiratory pathogens have been detected in the denture plaque and overnight denture wear has been linked to an increased risk of aspiration pneumonia. There is a general lack of evidence on the adequate management of denture stomatitis and we present a protocol for use in the primary care setting.

A review on influencing factors on the minimum inhibitory concentration of essential oils

With growing interest in essential oils as natural preservatives in the food industry, the literature is expanding enormously. To understand the antimicrobial activity of essential oils, the antimicrobial mechanism of individual essential oil (EO) compounds, and their minimum inhibitory concentrations (MICs), are interesting starting points for research. Therefore, and to get insight into the factors influencing their antimicrobial activities, the Web of Science was searched for MICs of EO compounds (1995-2016). Many MICs for individual EO compounds have already been reported in the literature, but there is large variability in these data, even for the MIC of the same compound against the same species. No correlation was found between the tested structural parameters of EO compounds (polarity, water solubility, dissociation constant, molecular weight and molecular complexity) and their MICs against all microorganisms, Gram-negative bacteria, Gram-positive bacteria and fungi. Few clear differences in sensitivity between microorganisms could be found. Based on this review it is clear that different incubation conditions, culture media and the use of emulsifiers/solvents have an influence on the MIC, causing big variance. This review points out the need for a good international standard method to assess the antimicrobial activity of EO compounds for better comparability between studies.

Antifungal Activity of Essential Oils against Candida albicans Strains Isolated from Users of Dental Prostheses

Objective

The objective of this study was to analyze the antifungal activity of citral, selected by screening natural products, against Candida albicans isolates from subjects who use dental prostheses.

Methodology

Screening of essential oils, including those from Mentha piperita L. (Briq), Origanum vulgare, and Zingiber officinale L., and the phytoconstituents citral and limonene, to select an appropriate natural product. Citral, which mediated the best antifungal response, was selected for biological assays. The minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) for citral and nystatin were determined by the microdilution method. Micromorphological analyses, time-kill curve, and modulation tests were performed.

Results

The MIC and MFC of citral were established as 32 μg/mL, consistent with fungicidal activity. The clinical strains were resistant to nystatin. Citral caused micromorphological alteration in the strains. In the time-kill curve, the growth of the clinical strain was reduction in growth equal to 3 log₁₀ colony-forming units per milliliter after exposure to the MIC and MIC × 2 of citral for 2 h. Citral did not modulate the resistance of the studied strains to nystatin.

Conclusion

This study revealed the potential of citral as a fungicidal agent and highlighted the resistance of clinical strains of C. albicans to nystatin.

Antimicrobial activity of eugenol and essential oils containing eugenol: A mechanistic viewpoint

Eugenol is a hydroxyphenyl propene, naturally occurring in the essential oils of several plants belonging to the Lamiaceae, Lauraceae, Myrtaceae, and Myristicaceae families. It is one of the major constituents of clove (Syzygium aromaticum (L.) Merr. & L.M. Perry, Myrtaceae) oil and is largely used in both foods and cosmetics as a flavoring agent. A large body of recent scientific evidence supports claims from traditional medicine that eugenol exerts beneficial effects on human health. These effects are mainly associated with antioxidant and anti-inflammatory activities. Eugenol has also shown excellent antimicrobial activity in studies, being active against fungi and a wide range of gram-negative and gram-positive bacteria. The aim of this review is to analyze scientific data from the main published studies describing the antibacterial and antifungal activities of eugenol targeting different kind of microorganisms, such as those responsible for human infectious diseases, diseases of the oral cavity, and food-borne pathogens. This article also reports the effects of eugenol on multi-drug resistant microorganisms. On the basis of this collected data, eugenol represents a very interesting bioactive compound with broad spectrum antimicrobial activity against both planktonic and sessile cells belonging to food-decaying microorganisms and human pathogens.

Honokiol induces reactive oxygen species-mediated apoptosis in Candida albicans through mitochondrial dysfunction

Objective

To investigate the effects of honokiol on induction of reactive oxygen species (ROS), antioxidant defense systems, mitochondrial dysfunction, and apoptosis in Candida albicans.

Methods

To measure ROS accumulation, 2′,7′-dichlorofluorescein diacetate fluorescence was used. Lipid peroxidation was assessed using both fluorescence staining and a thiobarbituric acid reactive substances (TBARS) assay. Protein oxidation was determined using dinitrophenylhydrazine derivatization. Antioxidant enzymatic activities were measured using commercially available detection kits. Superoxide dismutase (SOD) genes expression was measured using real time RT-PCR. To assess its antifungal abilities and effectiveness on ROS accumulation, honokiol and the SOD inhibitor N,N′-diethyldithiocarbamate (DDC) were used simultaneously. Mitochondrial dysfunction was assessed by measuring the mitochondrial membrane potential (mtΔψ). Honokiol-induced apoptosis was assessed using an Annexin V-FITC apoptosis detection kit.

Results

ROS, lipid peroxidation, and protein oxidation occurred in a dose-dependent manner in C. albicans after honokiol treatment. Honokiol caused an increase in antioxidant enzymatic activity. In addition, honokiol treatment induced SOD genes expression in C. albicans cells. Moreover, addition of DDC resulted in increased endogenous ROS levels and potentiated the antifungal activity of honokiol. Mitochondrial dysfunction was confirmed by measured changes to mtΔψ. The level of apoptosis increased in a dose-dependent manner after honokiol treatment.

Conclusions

Collectively, these results indicate that honokiol acts as a pro-oxidant in C. albicans. Furthermore, the SOD inhibitor DDC can be used to potentiate the activity of honokiol against C. albicans.