In vitro studies of activities of some antifungal agents against Candida albicans ATCC 10231 by the turbidimetric method

Eicosane: An antifungal compound derived from Streptomyces sp. KF15 exhibits inhibitory potential against major phytopathogenic fungi of crops

In the present scenario, food security is of major concern due to exponentially increasing population and depleted crop production. The fungal diseases have contributed majorly to the scarcity of staple food products and economic loss worldwide. This problem could be tackled by preventing the crop loss during both pre and post-harvest seasons. During the current investigation, the bioactive compound eicosane was extracted from Streptomyces sp. KF15, subjected to purification and identified based on mass spectrometry and NMR analysis. The evaluation of in-vitro antifungal activity was done by poisoned food method, SEM analysis and growth pattern analysis. The bioactive compound eicosane with molecular weight of 282.5475 g/mol was purified by column chromatography and the straight chain hydrocarbon structure of CH3CH2(18)CH3 was elucidated by NMR analysis. In poisoned food assay, eicosane effectively inhibited the radial growth of all tested fungal pathogens; F. oxysporum was found to be the most sensitive with 24.2%, 33.3%, 42.4%, and 63.6% inhibition at 25-100 μg/ml concentrations. The SEM micrograph established clear differences in the morphology of eicosane treated fungi with damaged hyphae, flaccid mycelium and collapsed spores as compared to the tubular, turgid and entire fungi in control sample. Finally, the growth curve assay depicted the right side shift in the pattern of eicosane treated fungi indicating the delay in adapting to the conditions of growth and multiplication. The findings of this study encourage further research and development towards the novel antifungal drugs that can act against major phytopathogens.

In-vitro investigation on the biological activities of squalene derived from the soil fungus Talaromyces pinophilus

The consistent increase in multidrug resistance among pathogens and increased cancer incidence are serious public health concerns and threaten humans by killing countless lives. In the present study, Talaromyces pinophilus CJ15 was characterized and evaluated for its antibacterial, candidicidal and cytotoxic activities. The selected isolate Talaromyces pinophilus CJ15 with 18S rRNA gene sequence of 1021 base pairs exhibited antifungal activity on plant pathogens via dual culture. The GC-MS profiling of crude extract illustrated the existence of many bioactive macromolecules which include squalene belonging to the terpenoids family. The biological macromolecules in the bioactive fraction of CJ15 exhibited increasing antibacterial activity with an increase in concentration such that the highest activity was recorded against Shigella flexneri with 15, 18, 20, and 24 mm inhibition zones at 25, 50, 75 and 100 μl concentrations, respectively. The squalene, having a molecular weight of 410.718 g/mol, displayed candidicidal activity with a right-side shifted log phase in the growth curve of all the treated Candida species, indicating delayed exponential growth. In cytotoxic activity, the extracted squalene exhibited an IC50 concentration of 26.22 μg/ml against JURKAT cells and induced apoptosis-induced cell death. This study's outcomes encourage the researchers to explore further the development of new and improved bioactive macromolecules that could help to prevent infections and human blood cancer.

Fungal Infected Adipose Stem Cells: The Effects of Novel Lipo-Niosome Nanoparticles Loaded with Amphotericin B and Thymus Essential Oil

OBJECTIVE

In this study, we aimed to develop new Lipo-niosomes based nanoparticles loaded with Amphotericin B (AmB) and Thymus Essential Oil (TEO) and test their effectiveness in the treatment of fungal-infected human adipose stem cells (hASCs).

MATERIALS AND METHODS

In this experimental study, optimal formulation of AmB and TEO loaded lipo-niosome (based on lipid-surfactant thin-film hydration method) was chemically, and biologically characterized. Therefore, encapsulation capacity, drug release, size, and the survival rate of cells with different concentrations of free and encapsulated AmB/ TEO were evaluated using the MTT method, and its antifungal activity was compared with conventional AmB.

RESULTS

Lipo-Niosome containing Tween 60 surfactant: cholesterol: Dipalmitoyl phosphatidylcholine (DPPC): Polyethylene glycol (PEG) with a ratio of 20:40:60:3 were chosen as optimal formulation. Lipo-Niosomes entrapment efficiency was 94.15%. The drug release rate after 24 hours was 52%, 54%, and 48% for Lipo-AmB, Lipo-TEO, and Lipo-AmB/TEO, respectively. Physical and chemical characteristics of the Lipo-Niosomes particles indicated size of 200 nm and a dispersion index of 0.32 with a Zeta potential of -24.56 mv. Furthermore, no chemical interaction between drugs and nano-carriers was observed. The cell viability of adipose mesenchymal stem cells exposed to 50 μg/ml of free AmB, free TEO, and free AmB/TEO was 13.4, 58, and 36.9%, respectively. Whereas the toxicity of the encapsulated formulas of these drugs was 48.9, 70.8, and 58.3% respectively. The toxicity of nanoparticles was very low (8.5%) at this concentration. Fluorescence microscopic images showed that the antifungal activity of Lipo-AmB/ TEO was significantly higher than free formulas of AmB, TEO, and AmB/TEO.

CONCLUSION

In this study, we investigated the efficacy of the TEO/AmB combination, in both free and encapsulatedniosomal form, on the growth of fungal infected-hASCs. The results showed that the AmB/TEO-loaded Lipo-Niosomes can be suggested as a new efficient anti-fungal nano-system for patients treated with hASCs.

Effects of tyrosol and farnesol on Candida albicans biofilm

The present in vitro study examined the effects of the quorum‑sensing molecules farnesol and tyrosol on the development of Candida albicans biofilm in order to elucidate their role as novel adjuvants in oral hygiene. The investigation was conducted in C. albicans ATCC 10231 and C. albicans isolates from dentures and was performed in flat‑bottomed 96‑well polystyrene plates. Yeast growth and their capacity to form biofilms were evaluated following 24 and 48 h incubations at 37˚C in Sabouraud broth supplemented with 0.001‑3 mM farnesol and/or 1‑20 mM tyrosol. Yeast growth was assessed by turbidimetry and biofilms were quantitated by crystal violet staining, under aerobic and anaerobic conditions. The viability of the fungal cells was controlled by the culture of planktonic cells and by examination of the biofilms using fluorescence microscopy following staining with fluorescein diacetate and ethidium bromide. Farnesol at 3 mM exerted a stronger action when added at the beginning of biofilm formation (>50% inhibition) than when added to preformed biofilms (<10% inhibition). Similarly, tyrosol at 20 mM had a greater effect on biofilm formation (>80% inhibition) than on preformed biofilms (<40% inhibition). Despite significant reductions in attached biomass, yeast growth varied little in the presence of the investigated molecules, as corroborated by the turbidimetry, culture of supernatants on solid culture medium followed by counting of colony‑forming units and viability tests using fluorescence microscopy. At the highest tested concentration, the molecules had a greater effect during the initial phases of biofilm formation. The effect of farnesol during anaerobiosis was not significantly different from that observed during aerobiosis, unlike that of tyrosol during anaerobiosis, which exhibited slightly reduced yeast biofilm inhibition. In conclusion, the present study demonstrated the specific anti‑biofilm effect, independent of fungicidal or fungistatic action, of farnesol and tyrosol, as tested in C. albicans ATCC 10231 and 6 strains isolated from dentures. Prior to suggesting the use of these molecules for preventive purposes in oral hygiene, further studies are required in order to clarify the metabolic pathways and cellular mechanisms involved in their antibiofilm effect, as well as the repercussions on the oral microbiome.

Ex vivo decontamination of yeast-colonized dentures by iodine-thiocyanate complexes

Introduction

Under well-defined experimental conditions, and in the presence of hydrogen peroxide, lactoperoxidase produces stable iodine-thiocyanate complexes that have antimicrobial properties. A novel process was developed to short circuit the consumption of hydrogen peroxide by microbial catalases by producing iodine-thiocyanate complexes prior to contact with microorganisms, with the aim of being able to decontaminate the ex vivo dentures colonized by yeasts.

Materials and methods

Teabags containing lactoperoxidase adsorbed on inert clay beads were immersed for 1 minute in phosphate buffer solution (0.1 M pH 7.4) containing 5.2 mM potassium iodide, 1.2 mM potassium thiocyanate, and 5.5 mM hydrogen peroxide. After removing the adsorbed lactoperoxidase, the stability and efficacy of iodine-thiocyanate complexes for Candida-colonized denture decontamination were verified. Investigations were performed in vitro on Candida albicans ATCC 10231 and on clinical isolates from 46 dentures. A Candida plate count was performed after a 24-hour incubation at 37°C on Sabouraud-chloramphenicol or CHROMagar solid media; then, the yeast growth was evaluated in Sabouraud broth by turbidimetry and biofilm biomass by crystal violet staining.

Results

In vitro tests demonstrated the effectiveness of the oxidant solution in sterilizing a suspension of 10⁶Candida cells per milliliter after a 5-minute incubation. A single ex vivo immersion of contaminated dentures in a solution of iodine-thiocyanate complexes led to a decrease of at least 1 log unit in the number of colony-forming units in 58.3% of the tested dentures, while immersing in water alone had no effect on denture colonization (significant c2: p = 0.0006).

Conclusion

These data suggest a promising new strategy for decontamination of dentures.

Origanum vulgare essential oil affects pathogens causing vaginal infections

AIMS

This study aimed to investigate the application of Origanum vulgare L. essential oil (EO) as an alternative antimicrobial agent against vaginal infections.

METHODS AND RESULTS

Microdilution methods were applied for the detection of the minimal inhibitory (MIC) and the minimal bactericidal/fungicidal (MBC/MFC) concentration of 15 clinical strains originating from women with symptoms of vaginal infection. Optical density determination (OD) was used for detection of the Candida growth rate. Staining with DAPI was used to detect the influence of EO on nuclear condensation and fragmentation, while the brine shrimp bioassay was used to determine the toxicity of EO. Chemical composition analysis was done using GS-MS. According to the MIC and MBC/MFC values, the most susceptible strains to EO were: Escherichia coli 1, E. coli 2, Staphylococcus aureus 3 and Candida albicans 1-3. Inhibition of C. albicans filamentation was detected at 0·45 μl ml^-1 .

CONCLUSIONS

The obtained inhibition (%) from Candida growth curves points to a shorter period of time (24 h) for determining IC₅₀ as MIC and IC₉₉ as MFC value. These values could be recommended as valid parameters for the faster detection of the effectiveness of EO on Candida isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

Examination of potential of the O. vulgare EO as a main antimicrobial constituent within vaginalettes in gynaecological practice.

Candida albicans adhesion to and invasion and damage of vaginal epithelial cells: stage-specific inhibition by clotrimazole and bifonazole

Clotrimazole and bifonazole are highly effective antifungal agents against mucosal Candida albicans infections. Here we examined the effects of low levels of clotrimazole and bifonazole on the ability of C. albicans to adhere, invade, and damage vaginal epithelial cells. Although adhesion and invasion were not affected, damage was greatly reduced upon azole treatment. This clearly indicates that low levels of azoles influence specific activities of C. albicans during distinct stages of vaginal epithelium infections.

Effect of ritonavir and saquinavir on Candida albicans growth rate and in vitro activity of aspartyl proteinases

An in vitro study to evaluate the antifungal effect and activity of aspartyl proteinases of the HIV-proteinase inhibitors ritonavir and saquinavir was conducted. Ritonavir diminished the growth rate of Candida albicans as well as the activity of its secreted aspartyl proteinases (Saps) in a nitrogen-limited medium, yeast carbon base and bovine serum albumin (YCB-BSA). This inhibition occurred in a dose-dependent fashion; with 8 mg l(-1) of ritonavir a partial growth inhibition (44%) was produced. The growth rate of C. albicans in medium with saquinavir was similar to that seen in the control, and Sap activity was inhibited only at high concentrations. In conventional medium (RPMI-1640), which does not induce the production of yeast proteases, no inhibitory effect was detected with either HIV-protease inhibitor.

Comparison of three methods of determining MICs for filamentous fungi using different end point criteria and incubation periods

Three different methods were used to determine the in vitro activities of amphotericin B, ketoconazole, itraconazole, and flucytosine against 30 isolates of different genera of filamentous fungi. MICs were determined visually, with or without agitation, and spectrophotometrically by using a broth microdilution method. For amphotericin B, there was one end point reading criterion (the minimum concentration of antifungal that inhibited 100% of growth), but for azoles and flucytosine there were two (the minimum concentrations that inhibited 50 and 75% of fungal growth, respectively) after 48 and 72 h of incubation. All tests were performed in triplicate. An intraclass correlation coefficient (ICC) was used to evaluate the reproducibility of each of the methods and the correlation among them. The reproducibility of the three methods was very high (ICC of 0.808 to 0.992), particularly in the case of azoles and flucytosine. In general, the degree of reproducibility was highest for azoles and amphotericin B after 72 h of incubation and for flucytosine after 48 h of incubation. The degree of correlation among the three methods was very high (ICC of >0.98) with all of the antifungals under all the conditions tested. The end point reading criteria and the time of incubation affected neither the reproducibility of the methods nor their correlation, and their effect on MICs was statistically significant.

Influence of incubation time, inoculum size, and glucose concentrations on spectrophotometric endpoint determinations for amphotericin B, fluconazole, and itraconazole

We addressed the influence of the incubation time (24 h versus 48 h), starting inoculum size (standard inoculum size, approximately 10(3) CFU/ml, versus large inoculum size, approximately 10(4) CFU/ml), and supplementation with 2% glucose of RPMI 1640 medium on the spectrophotometric determination of the MICs of amphotericin B, fluconazole, and itraconazole. We compared the MICs determined spectrophotometrically with those determined by the standard broth macrodilution method (National Committee for Clinical Laboratory Standards approved guideline M27-A). The agreement between the results of the spectrophotometric and standard methods for amphotericin B testing was 100%; this agreement was independent of the inoculum size and incubation time. On the other hand, the agreement for the results for fluconazole testing and itraconazole testing was dependent on the inoculum size and incubation time. With large inoculum size, excellent agreement can be achieved at 24 h. With standard inoculum size, acceptable agreement can be achieved only at 48 h. In contrast to previous observations, the addition of 2% glucose did not have any significant impact on the growth density at 24 h, nor did it improve the agreement with the standard method. Furthermore, supplemental glucose might falsely elevate the MIC at 48 h.

Identification of an amphotericin B resistant strain of Candida albicans using a rapid 3H-glucose incorporation microassay

Using a 3H-glucose incorporation assay, antifungal sensitivity testing undertaken on an isolate of Candida albicans cultured from the blood of a bone marrow transplant patient documented resistance to amphotericin B but sensitivity to fluconazole and itraconazole. Information obtained from in vitro antifungal sensitivity testing can be used to direct in vivo antifungal therapy. Widespread application of standardized in vitro antifungal sensitivity testing is needed.

Testing susceptibility of Candida species to fluconazole and itraconazole using the microdilution assay

A microdilution system was established for testing the susceptibility of Candida species to fluconazole and itraconazole. The assay used a sodium phosphate-buffered (0.1 mol l-1) Casitone/glucose medium (pH 7.2) supplemented with potassium, iron, magnesium, trace elements and vitamins. Tests were read photometrically after 24 h, and the minimum inhibitory concentration (MIC) was defined as the IC90. In nearly all strains sharp end points were observed. The MICs against Candida species without any known pre-exposure to azoles were found to range from 0.2 to 1.56 micrograms ml-1 for fluconazole and from 2.3 to 12 ng ml-1 for intraconazole. For strains from candidosis patients refractory to treatment with fluconazole the MICs of fluconazole ranged from 6.25 to 100 micrograms ml-1, while those for itraconazole varied between 12 and > 450 ng ml-1. The strains did not respond congruent to both azoles. A similar disparity of the MICs was observed with Candida tropicalis and Candida krusei. The unusually low MICs of itraconazole were attained because (1) the dilution series was prepared from a preformed (concentrated) dilution series in 75% dimethylsulphoxide and not directly by serial dilution in the broth and (2) the incubation was performed in microtitre plates made of quartz glass rather than in the generally used polystyrene microtitre plates.

In vitro susceptibility of Candida species isolated from patients with haematological malignancies

Candida spp. (83 isolates including C. (Torulopsis) glabrata) were tested in vitro for their susceptibility to 5-fluorocytosine, amphotericin B, ketoconazole, itraconazole, fluconazole, and miconazole. The yeasts were isolated from clinical specimens, mostly from the lower respiratory tract, of 30 oncologic patients, 27/30 with haematological malignancies, during a 6-month period (December 1991-May 1992). Minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) values of the 6 drugs were obtained for each yeast using a microdilution broth method developed in our laboratory. Amphotericin B, and 5-fluorocytosine were active against the majority of the yeasts with MIC90/MFC90 values within achievable serum concentrations (3.12/6.25 micrograms ml(-1) and 0.625/0.625 micrograms ml(-1) respectively). Azole derivatives showed a species-specific activity. MFC values were two to four times higher than those of the MICs, confirming the fungistatic rather than fungicidal activity of azole derivatives. An interesting correlation was found when the in vitro susceptibility values of the isolates were compared with data of patients with or without antifungal prophylaxis or therapy during that period. In general, with respect to fluconazole, C. albicans strains isolated from patients who received no treatment showed MIC and MFC values lower than those obtained from patients who were under prophylaxis or treatment with this drug. Fluconazole administration appears to influence in vitro susceptibility testing.

New in vitro assay based on glucose consumption for determining intraconazole and amphotericin B activities against Aspergillus fumigatus

We developed a new in vitro method of evaluating antifungal molecules. Fungal growth was determined by measuring glucose consumption, the only carbon source in a synthetic medium. First, the growth of 12 Aspergillus fumigatus strains was studied. Glucose consumption was an excellent indicator of fungal growth. Second, the partial inhibition of growth was calculated in terms of the 90% or 50% inhibitory concentration for the 12 strains after treatment with itraconazole and amphotericin B. With a 3-day incubation time, the calculated 90% and 50% inhibitory concentrations agreed with those obtained by a macromethod and with those reported in previous publications. In each case the high degrees of efficacy of itraconazole and amphotericin B against A. fumigatus were confirmed. Partial inhibition induced by low concentrations of antifungal agents was quantifiable by this new method.

Comparison of in vitro antifungal activity of itraconazole and hydroxy-itraconazole by colorimetric MTT assay

The in vitro antifungal activities of itraconazole and its active hydroxyl metabolite, hydroxy-itraconazole (R 63372), against Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans were compared by visual assessment of growth as well as by colorimetric MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide] assay using microtitre plates containing four different media. Minimum inhibitory concentration (MIC) end points determined by the colorimetric MTT assay correlated well with those obtained by visual assay. The two drugs showed different MIC values depending on the medium used. The activity of itraconazole was equal to or greater than the activity of hydroxy-itraconazole against most of the fungi tested. Both drugs showed lower MIC values against A. fumigatus and Cr. neoformans in brain heart infusion broth (BHI) medium than in yeast nitrogen base (YNBG) medium, Sabouraud glucose broth (SAB) or "synthetic amino acid medium, fungal" (SAAMF). However, the MIC end point of these drugs against C. albicans in BHI and SAB media was difficult to determine visually as well as by MTT assay. In C. albicans, the MTT assay method using SAAMF and YNBG media is recommended for the determination of MICs.

Antifungal susceptibility testing

Unlike antibacterial susceptibility testing, reliable antifungal susceptibility testing is still largely in its infancy. Many methods have been described, but they produce widely discrepant results unless such factors as pH, inoculum size, medium formulation, incubation time, and incubation temperature are carefully controlled. Even when laboratories agree upon a common method, interlaboratory agreement may be poor. As a result of numerous collaborative projects carried out both independently and under the aegis of the Subcommittee on Antifungal Susceptibility Testing of the National Committee for Clinical Laboratory Standards, the effects of varying these factors have been extensively studied and a standard method which minimizes interlaboratory variability during the testing of Candida spp. and Cryptococcus neoformans has been proposed. This review summarizes this work, reviews the strengths and weaknesses of the proposed susceptibility testing standard, and identifies directions for future work.

Turbidimetric and visual criteria for determining the in vitro activity of six antifungal agents against Candida spp. and Cryptococcus neoformans

The drug concentration which inhibited 50% of growth (IC50), the lowest drug concentration at which growth was less than 30% of that in a positive control well (IC30), the visual minimal inhibitory concentration (MIC), and the minimum fungicidal concentration (MFC), were applied to study the effects of fluconazole, itraconazole, ketoconazole, miconazole, flucytosine, and amphotericin B against 36 isolates of Candida spp. and Cryptococcus neoformans by a broth microdilution technique. When the recommendations established by the NCCLS Subcommittee on Antifungal Susceptibility Tests were applied for the visual reading of the microplates, the results were comparable with those obtained by the turbidimetric methods. Differences between MICs and IC30s were observed with miconazole against strains of C. glabrata (p = 0.014) and with flucytosine against strains of C. neoformans (p = 0.041). Differences between MICs and IC50s were observed with fluconazole against strains of C. albicans (p = 0.027), C. tropicalis (p = 0.046), and C. neoformans (p = 0.041); with miconazole against strains of C. glabrata (p = 0.014); and with amphotericin B against strains of C. parapsilosis (p = 0.025). Ten additional isolates of C. albicans from AIDS patients suffering from recurrent episodes of oral candidiasis and clinically resistant to fluconazole also were included in this study. The MICs of fluconazole of these strains were significantly higher than those of the control group (p = 0.003). When the turbidimetric parameters were applied for testing the in vitro activity of fluconazole against the above isolates, both IC30 and IC50 were capable of discriminating the strains of the two groups (p = 0.002, p = 0.001, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)