Agastache honey has superior antifungal activity in comparison with important commercial honeys

Abstract

There is an urgent need for new effective antifungal agents suitable for the treatment of superficial skin infections, since acquired resistance of fungi to currently available agents is increasing. The antifungal activity of mono-floral Agastache honey and commercially available honeys were tested against dermatophytes (T. mentagrophytes and T. rubrum) and C. albicans (ATCC 10231 and a clinical isolate) by agar well diffusion and micro-dilution (AWD and MD). In AWD and MD assays, Agastache honey was effective at 40% concentration against dermatophytes (zone diameter, 19.5-20 mm) and C. albicans with the same MIC and MFC values indicating fungicidal activity. Tea tree honey was effective at 80% concentration (zone diameter, 14 mm) against dermatophytes and at 40% concentration against T. mentagrophytes and C. albicans. Manuka was effective at 80% concentration only against T. mentagrophytes (zone diameter, 12 mm) and at 40% against T. rubrum and C. albicans with fungistatic activity. Similar to the AWD results, Jelly bush, Super Manuka, and Jarrah showed no activity against dermatophytes but showed some activity against C. albicans. Headspace volatiles of six honeys were isolated by SPME and identified by GC-MS. The characteristic chemical markers for each honey were as follows: Agastache- Phenol, 2,4-bis(1,1-dimethylethyl) and Estragole; Manuka and Tea-tree- Acetanisole and Methyl 3,5-dimethoxybenzoate; Jelly bush- Linalool and Nonanal; Super Manuka- Methyl 3,5-dimethoxybenzoate and Nonanal; Jarrah- Isophorone and Nonanoic acid. Overall, analysis of the bioactive compound content and antifungal activity of Agastache honey indicated possible use as an antifungal agent for management of superficial fungal infections.

Figure 1

Antifungal activity of honey against T. mentagrophytes determined by agar well diffusion. Honeys were tested in the range of 80–10% (w/v). Agastache honey exhibited the largest zone of inhibition at 40% concentration (20 mm) followed by tea-tree honey and Manuka honey at 80% concentration (14 mm and 12 mm, respectively).

Figure 2

Antifungal activity of honey against T. rubrum determined by agar well diffusion. Honeys were tested in the range of 80–10% (w/v). Agastache honey exhibited the largest zone of inhibition at 40% concentration (19.5 mm) followed by tea-tree honey at 80% honey (14 mm).

Figure 3

Antifungal activity of honeys measured by broth dilution. The graph shows the amount of growth (%) after exposure to honey at concentrations ranging from 0% to 40%. Agastache (square, black); Manuka (circle, red); Tea-tree (upwards triangle, blue); Jelly bush (downwards triangle, pink); Super Manuka (diamond, green); Jarrah (left triangle, navy) against T. mentagrophytes (a), T. rubrum (b), C. albicans ATCC 10231 (c) and a clinical isolate of C. albicans (d). Each point represents the mean of triplicate readings ± standard deviations (SD).

Figure 4

Effect of honey dilutions (40%) on the production of hydrogen peroxide (µM). Data represent the mean of triplicate readings ± standard deviations (SD).

Figure 5

HS-SPME GC-MS volatile compounds identified in Agastache honey. Compounds were identified with GC-MS reference libraries (Adams, Wiley 7th and NIST 2.0) using a 70% similarity match cut-off value. The peak area in the total ion chromatograms was the basis of calculations of concentration of studied compounds. The error bar represents the mean of triplicate readings ± standard deviations (SD). 1-Benzaldehyde, 2-D-Limonene, 3-Benzeneacetaldehyde, 4-Nonanal, 5-Phenylethyl Alcohol, 6-1H-Pyrazole, 4,5-dihydro-5,5-dimethyl-4-isopropylidene-, 7-Cyclopentasiloxane, decamethyl-, 8-4,Ketoisophorone, 9-Octanoic acid, ethyl ester, 10-Estragole, 11-Decanal, 12-Benzaldehyde, 4-methoxy, 13-Nonanoic acid, ethyl ester, 14-Benzene, 1-methoxy-4-propyl, 15-Phenol, 2,3,5-trimethyl-, 16-Nonanoic acid, 17-Propanoic acid, 2-methyl-, 2-ethyl-3-hydroxyhexyl ester, 18-2H-Benzimidazol-2-one, 1,3-dihydro-5-methyl-, 19-β-Caryophyllene, 20-Benzoic acid, 4-methoxy-, ethyl ester, 21-2-Propenoic acid, 3-phenyl-, ethyl ester, 22-Y-cadinene, 23-Phenol, 2,4-bis(1,1-dimethylethyl), 24-Benzoic acid, 3,5-dimethoxy-, methyl ester, 25-Dodecanoic acid, ethyl ester, 26-Y-Eudesmol, 27-Heptadecane, 28-Homosalate, 29-Nonadecane, 30-Hexadecanoic acid, ethyl ester, 31-Heneicosane, 32-9,12-Octadecadienoic acid (Z,Z). Data represent the mean of triplicate readings ± standard deviations (SD).

Figure 6

Detection of common volatile compounds by HS-SPME GC-MS in Leptospernum-origin honeys (Manuka, Tea-tree, Jelly bush and Super Manuka). Compounds were identified with GC-MS reference libraries (Adams, Wiley 7th and NIST 2.0) using a 70% similarity match cut-off value. The peak area in the total ion chromatograms was the basis of calculations of concentration of studied compounds. The relative % of common volatile compounds were calculated from the total peak area of the volatile compounds.

Figure 7

Volatile compounds identified in Jarrah honey by HS-SPME GC-MS. Compounds were identified with GC-MS reference libraries (Adams, Wiley 7th and NIST 2.0) using a 70% similarity match cut-off value. The peak area in the total ion chromatograms was the basis of calculations of concentration of studied compounds. The error bar represents the mean of triplicate readings ± standard deviations (SD). 1-Methane, thiobis-, 2-2-Butanone, 3-hydroxy-, 3-Acetyl valeryl, 4-(Z)-2-(Aminomethylene)-3,3-dimethylbutanenitrile, 5-4-Methyl-2-hexanol, 6-Benzaldehyde, 7-Cymene < Ortho > , 8-3-Cyclohexen-1-one, 3,5,5-trimethyl-, 9-Benzeneacetaldehyde, 10-Cymenene < Para- > , 11-Linalool, 12-Nonanal, 13-Isophorone, 14-Cyclopentasiloxane, decamethyl-, 15-Cyclohexanol, 4-(1-methylethyl), 16-Ethanone, 1-(1,4-dimethyl-3-cyclohexen-1-yl), 17-2-Hydroxy-3,5,5-Trimethyl-2-Cyclohexenone, 18-Octanoic Acid, 19-Terpineol < alpha- > , 20-Benzenemethanol, alpha., alpha, 4-trimethyl, 21-1,3-Cyclohexadiene-1-carboxaldehyde, 2,6,6-trimethyl, 22-Decanal, 23-Furan, 3-phenyl, 24-Cumin aldehyde, 25-Nonanoic acid, 26-Cymen-7-ol < Para- > 27-Thymol 28- Phenol, 2-methyl-5-(1-methylethyl) 29-Benzene, 2,4-diisocyanato-1-methyl, 30-Decanoic acid, 31-2-Propenoic acid, 3-phenyl- 32-2H-Benzimidazol-2-one, 1,3-dihydro-5-methyl- 33-9,9-dimethyl-9,-10-dihydroanthacene, 34-Pentadecane 35-Coumarin, 3,4-dihydro-4,4,7-trimethyl- 36-(+−)-(5,6,7,8-Tetrahydro-4-methyl-1-naphthalenyl)-1-ethanone 37-Benzoic acid, 3,5-dimethoxy-, methyl ester 38-Benzophenone 39-2-Cyclohexen-1-one, 3,5,5-trimethyl-4-(3-oxobutyl)- 40-1,2-Benzenedicarboxylic acid, bis(2-methylpropyl) ester, 41-Homo menthyl salicylate. Data represent the mean of triplicate readings ± standard deviations (SD).