Department of Microbiology, Nihon University School of Dentistry at Matsudo, 28701 Sakaecho-nishi, Matsudo City, Chiba 2718587, Japan
Received 25 June 2003; returned 26 August 2003, revised 26 October 2003; accepted 31 October 2003
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Abstract |
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Method: Antifungal activity was determined by broth dilution and calculation of cfu.
Results: The antifungal activity of catechin was pH dependent. The concentration of epigallocatechin gallate (EGCg) causing 90% growth inhibition of tested strains of C. albicans was 2000 mg/L at pH 6.0, 5001000 mg/L at pH 6.5 and 15.6250 mg/L at pH 7.0. Among catechins, pyrogallol catechin showed stronger antifungal activity against C. albicans than catechol catechin. The addition of 6.2525 or 3.1212.5 mg/L EGCg to amphotericin B 0.125 or 0.25 mg/L (below MIC) at pH 7.0 resulted in enhancement, respectively, of the antifungal effect of amphotericin B against amphotericin B-susceptible or -resistant C. albicans. Combined treatment with 3.1212.5 mg/L EGCg plus amphotericin B 0.5 mg/L (below MIC) markedly decreased the growth of amphotericin B-resistant C. albicans. When fluconazole-susceptible C. albicans was treated with 2550 mg/L EGCg and fluconazole 0.1250.25 mg/L (below MIC), its growth was inhibited by 93.0%99.4% compared with its growth in the presence of fluconazole alone. The combined use of 12.5 mg/L EGCg and fluconazole 1050 mg/L (below MIC) inhibited the growth of fluconazole-resistant C. albicans by 98.5%99.7%.
Conclusions: These results indicate that EGCg enhances the antifungal effect of amphotericin B or fluconazole against antimycotic-susceptible and -resistant C. albicans. Combined treatment with catechin allows the use of lower doses of antimycotics and induces multiple antifungal effects. It is hoped that this may help to avoid the side effects of antimycotics.
Keywords: Japanese green tea, polyphenols, antifungal effects, yeast
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Introduction |
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Amphotericin B is one of the polyene antibiotics, and fluconazole is an azole antifungal agent. They have strong antifungal activity, especially against C. albicans. However, they also have side effects,7 and antimycotic-resistant clinical isolates of C. albicans have appeared.8,9 Therefore, a non-antibiotic agent that is both highly effective and safe might be important for the eradication of both antibiotic-susceptible and -resistant strains of C. albicans. There are several reports that show antifungal activity by natural products.1014 Green tea is a natural substance that is commonly drunk worldwide, especially in Asia. Catechin from tea has been reported to have an antimicrobial effect against oral,15,16 intestinal17 and food-borne18 bacteria, antitoxicity against various bacterial haemolysins19 and antiviral activity.20
In this study, we examined the antifungal effects on C. albicans of tea catechins on their own and combined with antimycotics.
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Materials and methods |
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Candida albicans ATCC 90028, ATCC 90029, ATCC 96901 and ATCC 200955, and 10 clinical isolates were used in this study. All strains were maintained routinely and cfu were calculated on Sabouraud agar (Nissui Co., Tokyo, Japan). The plates were incubated aerobically at 37°C for 48 h.
Catechins and antimycotics
The catechins used in this study were ()-epigallocatechin gallate (EGCg), ()-epicatechin gallate (ECg), ()-epigallocatechin (EGC), ()-epicatechin (EC), (+)-catechin (C), catechin gallate (Cg), (+)-gallocatechin (GC) and gallocatechin gallate (GCg), and they were purchased from Funakoshi Co. (Tokyo, Japan). Amphotericin B and fluconazole were purchased from Sigma Chemical Co. (St Louis, MO, USA).
Measurement of MIC of EGCg at various pHs
Measurement of the MIC of EGCg for C. albicans was performed by broth dilution and calculation of cfu. In the experiments, RPMI medium 1640 (Gibco BRL) buffered with 0.15 M sodium phosphate buffer (NaPB-RPMI) at pH 6.0, 6.5 or 7.0 was used for the test medium. The experimental medium was prepared by twofold dilution of 8000 mg/L EGCg with NaPB-RPMI at pH 6.0, 6.5 or 7.0. C. albicans was pre-incubated in the NaPB-RPMI and buffered at each pH at 37°C for 24 h with shaking (100 strokes/min). The pre-cultured C. albicans (final fungal count of 1 x 103 cfu/mL) was inoculated into 1 mL of the experimental media at various pHs. After cultures were shaken at 37°C for 48 h, they were spread on Sabouraud agar plates at 10-fold dilutions in triplicate. The plates were incubated at 37°C for 48 h under aerobic conditions. Antifungal activity was determined by calculation of cfu. The minimum concentration that inhibited the growth of C. albicans on the Sabouraud agar plates by 90%, compared with the growth in EGCg-free medium, was defined as the MIC90.10 The minimum fungicidal concentration (MFC) was determined as the lowest concentration resulting in the death of 99.9% or more of the initial inoculum. To determine MFCs, 0.1 mL of the test sample was inoculated on Sabouraud agar plates in triplicate and incubated at 37°C for 48 h. The cfu were counted to assess viability.10
Assay of antifungal activity of catechins
To investigate the effect of catechins on non-multiplying fungal cells, resting fungal cells were prepared. C. albicans was cultured in brain heart infusion (BHI, Difco Laboratories, Detroit, MI, USA) broth at 37°C for 24 h aerobically with shaking. The growing cells were harvested, washed three times with 0.15 M NaPB (pH 7.0), suspended in the same buffer to a final concentration of 1 x 106 cfu/mL and used for the assay. One milligram per mL of each catechin was added to the resting cells (
1 x 106 cfu/mL) in NaPB, pH 7.0, and the mixture was incubated at 37°C with shaking. Aliquots (0.1 mL) of the cell suspensions were collected over an extended period. Ten-fold dilutions of the samples were made in 0.9 mL of TrisHCl buffer (0.05 M, pH 7.0) and inoculated onto Sabouraud agar plates. The plates were cultured aerobically at 37°C for 48 h and the cfu calculated.
Measurement of multiple effects of EGCg and antimycotics
Assays of antifungal activity against C. albicans were performed in a similar manner to that described above for the measurement of MIC. Catechins, amphotericin B and fluconazole were prepared at 503.12, 0.50.125 and 500.125 mg/L in NaPB-RPMI at pH 7.0. At these concentrations, none of the agents alone affects the growth of C. albicans. The pre-cultured C. albicans (2 x 107 cfu/mL) was adjusted to
2 x 103 cfu/mL with NaPB-RPMI at pH 7.0 using the 10-fold dilution method for inoculation. One millilitre of these diluted solutions of C. albicans was added to 1 mL of the mixtures of various concentrations of EGCg and antimycotic solutions in NaPB-RPMI at pH 7.0. After shaking incubation at 37°C for 48 h, the cultures were spread on plates at 10-fold dilutions in triplicate, and the cfu calculated. The percentage of growth inhibition was calculated from the cfu compared with that of drug-free control cultures.
Statistical analysis
Data shown are from three separate experiments and were analysed statistically by calculating means and S.D. of the means. The differences were evaluated by Students t-test.
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Results |
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The MIC90 and MFC of EGCg for C. albicans ATCC 90028, ATCC 90029, ATCC 96901 and ATCC 200955 are shown in Table 1. The antifungal effect of EGCg was dependent on pH. The MIC90 of EGCg at pH 6.0 against ATCC 90028, ATCC 90029, ATCC 96901 and ATCC 200955 strains was 2000 mg/L. However, at pH 7.0 it was 15.6250 mg/L. The MFC of EGCg against the test strains was 40008000 mg/L at pH 6.0 and 1252000 mg/L at pH 7.0. Strain ATCC 96901, which is fluconazole resistant, was slightly more susceptible to EGCg than the other strains. Table 2 shows the MIC90 of EGCg for clinical isolates of C. albicans at pH 7.0. The range of MIC90 values was 31.2250 mg/L. The MIC90 of fluconazole and amphotericin B for strain ATCC 90029 at pH 7.0 was 0.51 mg/L and 0.250.5 mg/L, respectively (data not shown).
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Figure 1 shows the antifungal effects of the various catechins on resting fungal cells of C. albicans ATCC 90029. The survival of resting cells decreased immediately and rapidly with EGC, GC, EGCg and GCg, and the survival rate was <1% after 4 h. A few colonies still survived after 24 h of culturing. In contrast, the survival of resting cells treated with C, EC, Cg and ECg had hardly decreased after 4 h, but decreased gradually and slowly with increasing incubation time. The survival rate was 1%10% after 24 h of culturing.
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Effect of EGCg on the antifungal activity of antimycotics
The addition of EGCg to amphotericin B resulted in enhancement of the antifungal activity of amphotericin B (Figures 2 and 3). Amphotericin B at 0.125 and 0.25 mg/L in the presence of 6.25 mg/L EGCg caused, respectively, 94.2% and 99.5% inhibition of the growth of amphotericin B-susceptible ATCC 90029. Stronger growth inhibition was obtained with 25 mg/L EGCg. The ATCC 90029 strain grew to only 0.2% or 0.01% of the extent seen with amphotericin B alone. The addition of 3.12 mg/L EGCg to amphotericin B 0.25 or 0.5 mg/L inhibited the growth of amphotericin B-resistant C. albicans ATCC 200955, resulting in, respectively, 0.04% or 0.001% of the extent of growth seen with amphotericin B alone. A stronger synergic effect of EGCg was obtained using 12.5 mg/L with amphotericin B 0.25 and 0.5 mg/L. The growth level of the ATCC 200955 strain was 3.4 x 102 and 8.3 x 10 cfu at these concentrations, whereas that of the control was 5 x 107 cfu.
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Discussion |
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For reference, a normal cup of tea has a concentration of 1000 p.p.m. polyphenol. The catechins extracted from Japanese green tea consist of mainly EGCg, EGC and GC, and minor amounts of EC, ECg and C. Cg and GCg are not contained in extracts from green tea. Among these catechins, pyrogallol catechins (EGCg, EGC, GC and GCg) were more effective than catechol catechins (EC, ECg, C and Cg) against C. albicans (Figure 1). The actions of EGCg, EGC and GC were fungicidal. Studies of the antibacterial activity of catechins against phytopathogenic bacteria showed results similar to those against C. albicans.22 Ikigai et al. 24 reported that the mechanism of the bactericidal effects of catechins primarily involved acting on and damaging bacterial membranes of Staphylococcus aureus and Escherichia coli. The antibacterial activities of catechins were predominantly related to the gallic acid moiety and the hydroxyl group member.24 The mode of catechin action involves inducing rapid leakage of small molecules entrapped in the intraliposomal space and aggregation of the liposomes.24 Toyoshima et al.25 examined the mechanism of the effects of green tea catechin on T. mentagrophytes using electron microscopy and suggested that catechin attacked the cell membrane and caused lysis of the conidia and hyphae.
The present study also showed synergic antifungal activity of the combination of EGCg and antimycotics against C. albicans. Amphotericin B possesses antifungal activity against C. albicans. However, amphotericin B has strong side effects even at low doses. The combination of amphotericin B and 5-fluorocytosine, an antimycotic, was tried in an attempt to reduce the effective dose of amphotericin B.26 In the present study, the combined use of EGCg and amphotericin B (below MIC) inhibited the growth of C. albicans, and the action was fungicidal. Amphotericin B binds to ergosterol, one of the cell membrane sterols, and damages the cell membrane directly, leading to fungicidal activity against the fungi. Amphotericin B below the MFC also stimulates fungal membrane permeability. The combined use of amphotericin B and catechin may stimulate catechin uptake into the cell by the action of amphotericin B, and intracellular catechin may act as a fungicidal agent. A similar finding was reported previously. Catechin induces antibacterial activity of oxacillin below the MIC against methicillin-resistant S. aureus.27 The bactericidal mechanism may be as follows: first, catechin acts on and damages bacterial membranes, and second, oxacillin binds to penicillin-binding protein and deactivates bacteria.24 Since the arrival of azole antifungal agents as first-line drugs,28 fluconazole-resistant C. albicans has begun to appear.8 The combined use of EGCg and fluconazole was effective even against fluconazole-resistant C. albicans. The effective dose of fluconazole was decreased to one-fortieth using 6.25 mg/L EGCg compared with the growth in the presence of fluconazole alone (Figure 5). C. albicans expresses multidrug efflux transporter (MET), which mediates the efflux of a broad range of compounds, including fluconazole. MET inhibitor, cyclosporine, and fluconazole showed a potent synergic effect against C. albicans.29 The mechanism of the synergic effect of the combination of fluconazole and EGCg is still unknown.
C. albicans superinfection results from taking antibiotics for a long period, and is predominately detected in the oral cavity, intestine and vagina. Local administration of amphotericin B and fluconazole is very effective against C. albicans. The addition of catechin to amphotericin B or fluconazole induces antifungal activity via stimulation of multiple functions (Figures 25). Catechins are not destroyed and retain their effectiveness when exposed to artificial gastric juice for over 60 min (data not shown). Catechin combined with amphotericin B or fluconazole, and perhaps other antimycotics, may be beneficial and may contribute to the effective medical treatment of candidoses, such as thrush, denture stomatitis, and intestinal candidosis. However, in vivo experiments would be needed to test these possibilities in living animals or humans.
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Acknowledgements |
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Footnotes |
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