Elsevier

Food Chemistry

Volume 261, 30 September 2018, Pages 233-239
Food Chemistry

Chemical composition, antifungal activity and potential anti-virulence evaluation of the Eugenia uniflora essential oil against Candida spp.

https://doi.org/10.1016/j.foodchem.2018.04.015Get rights and content

Highlights

  • The essential oil of Eugenia uniflora presented two components with proven antifungal activity: selina-1,3,7 (11)-trien-8-one and selina-1,3,7 (11)-trien-8-one.

  • Essential oil of Eugenia uniflora presented an antagonistic effect in association with Fluconazol.

  • The performance of E. uniflora essential oil was considered as a fungistatic agent.

  • The natural product inhibited one of the virulence mechanisms of Candida spp. which is the proliferation of filamentous structures.

Abstract

The development of fungal resistance to antifungal drugs has been worsening over the years and as a result research on new antifungal agents derived from plants has intensified. Eugenia uniflora L. (pitanga) has been studied for its various biological actions. In this study the chemical composition and antifungal effects of the E. uniflora essential oil (EULEO) were investigated against Candida albicans (CA), Candida krusei (CK) and Candida tropicalis (CT) standard strains. The essential oil obtained through hydro-distillation was analyzed by gas chromatography coupled to mass spectrometry (GC-MS). To determine the IC50 of the oil, the cellular viability curve and the inhibitory effects were measured by means of the oil’s association with Fluconazole in a broth microdilution assay with spectrophotometric readings. The Minimum Fungicidal Concentration (MFC) was determined by solid medium subculture with the aid of a guide plate while the assays used to verify morphological changes emerging from the action of the fractions were performed in microculture chambers at concentrations based on the microdilution. Two major oil constituents stand out from the chemical analysis: selina-1,3,7(11)-trien-8-one (36.37%) and selina-1,3,7(11)-trien-8-one epoxide (27.32%). The concentration that reduced microorganismal growth was ≥8,192 μg/mL while the IC50 varied, this being between 1892.47 and 12491.80 μg/mL (oil), 10.07 – 80.78 μg/mL (fluconazole) and 18.53 – 295.60 μg/mL (fluconazole + oil). The combined activity (fluconazole + oil) resulted in indifference and antagonism. A MFC of the oil in association with fluconazole was recorded at the concentration of 8,192 μg/mL against CA and CK. The oil caused the inhibition of CA and CT morphological transition. In view of the results obtained, additional research is needed to elucidate the activity of the E. uniflora oil over genetic and biochemical processes regarding its effect on Candida spp. virulence.

Introduction

Fungi from the Candida genus are very common as they are part of the normal human microbiota and can be isolated in the most diverse anatomical sites; in the mouth, for example, around 20 to 50% of healthy teeth are colonized by Candida spp. These are yeast fungi whose most well-known species, Candida albicans, is usually associated with pathological conditions, however, other species such as C. tropicalis, C. glabrata and C. krusei, are frequently identified (Zomorodian et al., 2011).

Fungal infections caused by opportunistic pathogens have become increasingly frequent, especially as a result of the relentless use of antimicrobial therapies and an increase in the number of immunocompromised patients. While some Candida species form part of the natural human microbiota, these can also become pathogenic, often in association with virulence factors from the microorganism itself, due to immunological conditions of the individual (Chaves, Santos & Colombo, 2012). Among the main virulence factors associated with the Candida genus, are: epithelial cell adhesion; hydrolytic enzyme secretions such as proteases, phospholipases and hemolysins; biofilm formation; phagocytic cell evasion and transitioning between yeast and hyphal states (Chaves et al., 2013).

The choice of initial antimycotic agent for the treatment of a suspected invasive Candida infection is also difficult. The development of resistance to antifungal agents used in Candida treatment is a situation which has been worsening. Prophylaxis with fluconazole in the last two decades is suggested to have led to an increase in non-albicans species prevalence with a reduced susceptibility to this drug (Perfect, 2004).

In this sense, by utilizing the rich Brazilian flora, research for new antifungal agents derived from plant extracts and essential oils has intensified due to the relatively small arsenal of drugs available for the treatment of mycoses, mainly due to the problem involving the resistance of strains to these (Eddouzi et al., 2013).

Eugenia uniflora L., popularly known as pitanga, is an arboreous plant from the Myrtaceae family which is widely distributed in Brazil and other South American countries. Several plant phytoconstituents of this plant have been studied, such as flavonoids, mono and triterpenoid compounds, tannins, anthraquinones, cineol and essential oils, the results of which proposed that in addition to presenting antimicrobial activity, the species presents several biological actions, such as antioxidant, antihypertensive and diuretic actions (Amorim, Lima, Hovell, Miranda, & Rezende, 2009).

The objective of this study was to investigate the chemical composition and in vitro effect of the Eugenia uniflora essential oil, both alone and in combination with fluconazole, on the growth inhibition and drug action potentiation against Candida spp, as well as to verify the inhibition of fungal pleomorphism, a virulence factor of yeasts.

The association of the E. uniflora essential oil at a subinhibitory concentration with fluconazole to verify the modulating effect is unprecedented.

Section snippets

Collection area

The plant material was collected from an urban area in the municipality of Crato, south of Ceará, Brazil (317 m, 07°,14′,08.4″ South latitude and 39°,24′,57″ West of Greenwich). The collection period included January, February, March and April. The samples were collected between 08:30 and 10:30 in the morning. From the collected material, an exsiccate was prepared which was later identified and deposited in the Caririense Dárdano de Andrade-Lima Herbarium (HCDAL) of the Regional University of

Chemical analysis

Table 1 shows the composition of the essential oil evaluated, determined by gas chromatography (GC/MS). In this study, we identified 09 compounds, representing 87.71% of the total composition. Of the components identified, two stand out: selina-1,3,7(11)-trien-8-one (36.37%) and selina-1,3,7(11)-trien-8-one epoxide (27.32%). The chemical composition identified partially corroborates with other studies that describe the chemical composition of the E. uniflora essential oil (Weyerstahl et al.,

Conclusion

High concentrations of the E. uniflora essential oil were required to obtain an antifungal effect. The combination of the oil and fluconazole did not show synergism, however good results were obtained especially in relation to inhibition of the C. albicans and C. tropicalis morphological transition process, which in human infections can cause tissue invasion. Further research is needed to understand the oil activity over the fungi biochemical and genetic processes related to fungal virulence

Declaration of interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.

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