Wylly Araújo de Oliveira

Antifungal Activity of Thymus vulgaris L. Essential Oil and Its Constituent Phytochemicals against Rhizopus oryzae: Interaction with Ergosterol

Mucormycoses are emerging infections that have high rates of morbidity and mortality. They show high resistance to antifungal agents, and there is a limited therapeutic arsenal currently available, therefore, there is a great need to give priority to testing therapeutic agents for the treatment of mucormycosis. Along this line, the use of essential oils and phytoconstituents has been emphasized as a new therapeutic approach. The objective of this work was to investigate the antifungal activity of the essential oil (EO) of Thymus vulgaris, and its constituents thymol and p-cymene against Rhizopus oryzae, through microbiological screening, determination of minimal inhibitory concentration (MICs) and minimal fungicidal concentration (MFCs), effects on mycelial growth and germination of sporangiospores and interaction with ergosterol. The MIC of EO and thymol varied 128–512 µg/mL, but the MFC of EO and thymol varied 512–1024 µg/mL and 128–1024 µg/mL, respectively. The results also showed that EO and thymol significantly inhibited mycelial development and germination of sporangiospores. Investigation of the mechanism of antifungal action showed that EO and thymol interact with ergosterol. These data indicate that EO of T. vulgaris and thymol possess strong antifungal activity, which can be related to their interaction with ergosterol, supporting the possible use of these products in the treatment of mucormycosis.

Antifungal activity and mode of action of carvacrol against Candida albicans strains

In this study, the minimal inhibitory concentration (MIC), minimal fungicidal concentration (MFC) and mode of action of carvacrol were determined. MIC was determined according to the standard broth microdilution method, and MFC was taken as the lowest concentration in culture plates with Sabouraud dextrose agar, at which growth was less than 3 CFU. The effect of ergosterol or sorbitol on carvacrol was investigated using the broth microdilution method. MIC was 256 μg/mL and MFC was 512 μg/mL. This phytoconstituent acts by binding to sterols in the fungal membrane and does not act by modifying the fungal cell wall. This study is important because it shows the mode of action of carvacrol. However, more studies are necessary to define the exact mechanism of action.

Antifungal activity of Cymbopogon winterianus jowitt ex bor against Candida albicans

Candida albicans is an opportunistic yeast and a member of the normal human flora that commonly causes infections in patients with any type of deficiency of the immune system. The essential oils have been tested for antimycotic activity and pose much potential as antifungal agents. This work investigated the activity of the essential oil of Cymbopogon winterianus against C. albicans by MIC, MFC and time-kill methods. The essential oil (EO) was obtained by hydrodistillation using a Clevenger-type apparatus. It was tested fifteen strains of C. albicans. The MIC was determined by the microdilution method and the MFC was determined when an aliquot of the broth microdilution was cultivated in SDA medium. The phytochemical analysis of EO showed presence of citronellal (23,59%), geraniol (18,81%) and citronellol (11,74%). The EO showed antifungal activity, and the concentrations 625 µg/mL and 1250 µg/mL inhibited the growth of all strains tested and it was fungicidal, respectively. The antimicrobial activity of various concentrations of EO was analyzed over time, it was found concentration-dependent antifungal activity, whose behavior was similar to amphotericin B and nystatin.

Anti-Candida albicans effectiveness of citral and investigation of mode of action.

Context: Candidiasis is a mycosis caused by Candida species, which is of clinical importance due to the increase in resistant yeasts. Candida infection has been a serious health problem due to the inappropriate use of antibiotics. Therefore, it is necessary to study molecules with an antifungal action. Citral is a monoterpene with known pharmacological properties, including antimicrobial action. Objective: The aim of this work was to determine the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of citral and the probable mode of action. Materials and methods: The MIC of citral was determined by the broth microdilution method using Sabouraud dextrose medium. Additionally, the interference of citral in cell wall (sorbitol assay) and the binding of citral to ergosterol and cholesterol were studied, carried out by broth microdilution method. Results: The MIC and MFC of citral were 512 and 1024 µg/mL, respectively. The MIC of amphotericin B was 1 µg/mL. The mechanism of action did not involve either the cell wall or ergosterol. However, the presence of cholesterol increased the MIC of citral to 1024 µg/mL, indicating there is some interaction between citral and cholesterol. Amphotericin B was used as the positive control, and it showed a high MIC in the presence of ergosterol (32 µg/mL), while in the presence of cholesterol MIC increased to 4 µg/mL. Conclusion: Citral inhibits the growth of C. albicans. The probable mechanism of action did not involve the cell wall or ergosterol. Citral is able to interact with cholesterol. More studies are necessary to describe their effects completely.

Antifungal activity of geraniol and citronellol, two monoterpenes alcohols, against Trichophyton rubrum involves inhibition of ergosterol biosynthesis

Abstract Context: Trichophyton rubrum is the most common fungus causing chronic dermatophytosis in humans. Antifungal activity of promising agents is of great interest. Geraniol and citronellol are monoterpenes with antimicrobial properties. Objective: This study aimed to investigate the inhibitory effects and possible mechanism of antifungal activity of geraniol and citronellol against strains of T. rubrum. Materials and methods: The minimum inhibitory concentration (MIC) of each drug against 14 strains was determined by broth microdilution. The effects of the drugs on dry mycelial weight, conidial germination, infectivity on human nail fragments, and morphogenesis of T. rubrum were analyzed. The effects on the cell wall (test with sorbitol) and cell membrane (release of intracellular material and ergosterol biosynthesis) were investigated. Results: MIC values of geraniol ranged between 16 and 256 µg/mL while citronellol showed MIC values from 8 to 1024 µg/mL. The drugs (MIC and 2 × MIC) inhibited the mycelial growth, conidia germination, and fungal growth on nail fragments. The drugs (half of MIC) induced the formation of wide, short, and crooked hyphae in T. rubrum morphology. With sorbitol, geraniol MIC was increased by 64-fold and citronellol by 32-fold. The drugs caused leakage of intracellular material and inhibited ergosterol biosynthesis. Discussion: The results suggest that the drugs damage cell wall and cell membrane of T. rubrum through a mechanism that seems to involve the inhibition of the ergosterol biosynthesis. Conclusion: This study confirms that geraniol and citronellol can be regarded as potential drugs for controlling T. rubrum growth, with great potential against agents of dermatophytosis.

Investigation of the antifungal activity of carvacrol against strains of Cryptococcus neoformans

Abstract Background: Cryptococcus neoformans is the etiologic agent of opportunistic systemic fungal infection cryptococcosis, which affects individuals with compromised immune systems. Thus, natural products research has become important, since monoterpenes such as carvacrol, a promising molecule in the search antifungal agents, have shown significant biological activity. Objective: The study aimed to investigate the antifungal activity and mode of action of carvacrol against strains of C. neoformans. Methods: The minimum inhibitory concentration (MIC) was determined by microdilution method. Minimum fungicidal concentration (MFC) was performed by seeding technique on solid media. Studying the mode of action was performed using broth microdilution. Results: The MIC ranged from 25 to 81 μg/mL and the MFC ranged from 25 to 102 μg/mL. Carvacrol bonded to exogenous ergosterol and cholesterol. Discussion: The results suggest that carvacrol has antifungal activity against C. neoformans and its mode of action is related to fungal membrane instability. Conclusions: The phytoconstituent carvacrol may eventually become a drug; however, further studies are needed to elucidate its mechanism.

Effects of the essential oil of Cymbopogon winterianus against Candida albicans

Candida spp. are commensal and opportunistic pathogens virtually present in all humans. Candida albicans is pathogenic for man and became resistant to antifungal agents, therefore it is important in the search of new antifungals. The study aimed to investigate the mechanism of action of Cymbopogon winterianus essential oil against C. albicans. Morphological changes were observed in C. albicans when exposed to several concentrations of oil by microculture technique for yeasts, using agar-rice in moist chamber. Cellular leakage was analyzed after cell lysis by absorbing compounds at 260 nm; it was also assessed the bind of essential oil with ergosterol. C. winterianus essential oil inhibited the formation of pseudohyphae and chlamydoconidia in all concentrations tested, it caused cellular lysis and the minimum inhibitory concentration of the oil in presence of ergosterol increased until eight times, indicating binding to ergosterol.