Assessment of Antimicrobial Activity of Fourteen Essential Oils When Using Dilution and Diffusion Methods

Figures & data

Table 1.. Plant species, family, common name, and lot or sample number for single (one species) and blended (two or more species) essential oils used in this study.

Single oils

Artemisia dracunculus. L. (Asteraceae), tarragon 11464

Aniba rosaeodora. Ducke (Lauraceae), rosewood 11423

Abies grandis. Gord. & Glend. (Pinaceae), white fir 11143

Lavandula angustifolia. L. (Lamiaceae), French lavender 11349

Melissa officinales. L. (Lamiaceae), Melissa 11028

Origanum vulgare. L. (Lamiaceae), Turkish oregano 11107

Picea mariana. BSP. (Pinaceae), spruce 11448

Satureja montana. L. (Lamiaceae), mountain savory 11346

Tanacetum vulgare. L. (Asteraceae), Idaho tansy 10347

Thymus vulgaris. L. (Lamiaceae), thyme 10347

Blended oils

Exodus II: Cinnamomum zeylanicum. Blume (Lauraceae), cinnamon; Acorus calamus. L. (Acoraceae), calamus; C. cassia. Nees & Eberum. (Lauraceae), cassia; Boswellia carteri;. Birdw. (Burseraceae), frankincense; Ferula gummosa. Boiss (Umbelliferae), galbanum; Hyssop officinalis. L. (Lamiaceae), hyssop; Commiphora myrrha. Holmes (Burseraceae), myrrh; Nardostachys jatamansi. D.C. (Valerianaceae), spikenard. VF5.

Peace & Calming: Cananga odorata. Hook. F. & Thomas (Annonaceae), ylang ylang; Citrus aurantium. L. (Rutaceae), orange; C. retisulata. Blanco (Rutaceae), tangerine; Pogostemon cablin. (Blanco) Benth. (Lamiaceae), patchouli. Sample 73.

Thieves: Cinnamomum zeylanicum. Blume (Lauraceae), cinnamon; Citrus limonum. Risso (Rutaceae), lemon; Eucalyptus radiata. DC (Myrtaceae), eucalyptus; Rosmarinus officinales. L. (Lamiaceae), rosemary; Syzygium aromaticum. Merr. & L. M. Perry (Myrtaceae), clove. 3140.

T. Wood: Artemisia absinthium. L. (Asteraceae), wormwood; Tanacetum vulgare. L. (Asteraceae), Idaho tansy. 11040.

Figure 1 Correlation between INT and OD measurements in determining the minimum inhibitory concentration (MIC) of 14 essential oils against Staphylococcus aureus. (A) and Candida albicans. (B).

Table 2.. Minimum inhibitory concentration (MIC) of 14 essential oils against Staphylococcus aureus. as determined by the metabolic dye (INT) and % inhibition (OD).

	MIC (INT dye^a.)		MIC % inhibition^b.
Essential oil		Range		Range
Thyme	0.31	0.31	0.31	0.31
Mountain savory	0.31	0.31	0.31	0.31
Turkish oregano	0.42	0.31–0.63	0.42	0.31–0.63
T1	1.04	0.63–1.25	1.04	0.63–1.25
Tarragon	1.88	0.63–2.50	1.04	0.63–1.25
Melissa	1.88	0.63–2.50	1.04	0.63–1.25
Rosewood	2.50	2.50	2.50	2.50
TW4	2.50	2.50	2.50	2.50
White fir	2.71	0.63–5.00	2.71	0.63–5.00
Spruce	3.33	2.50–5.00	2.08	1.25–5.00
Idaho tansy	3.33	2.50–5.00	3.33	2.50–5.00
PC3	4.17	2.50–5.00	3.33	2.50–5.00
French lavender	4.17	2.50–5.00	4.17	2.50–5.00
E2	6.67	5.00–10.00	8.33	5.00–10.00

T1 = Thieves; E2 = Exodus II; PC3 = Peace & Calming; TW4 = T. Wood (see Table 1).

^a.As determined by the lack of INT reduction to INT formazan; n = 3 for each oil.

^b.As determined by OD readings at 600 nm; n = 3 for each oil.

Table 3.. Minimum inhibitory concentration (MIC) of 14 essential oils against Candida albicans. as determined by the metabolic dye (INT) and % inhibition (OD).

	MIC (INT dye^a.)		MIC % inhibition^b.
Essential oil		Range		Range
Thyme	0.31	0.31	0.31	0.31
Turkish oregano	0.31	0.31	0.42	0.31–0.63
Mountain savory	0.42	0.31–0.63	0.42	0.31–0.63
Melissa	1.25	1.25	1.25	1.25
T1	1.67	1.25–2.50	1.67	1.25–2.50
E2	1.67	1.25–2.50	1.67	1.25–2.50
Tarragon	1.67	1.25–2.50	1.67	1.25–2.50
TW4	2.50	2.50	2.50	2.50
Idaho tansy	3.33	2.50–5.00	3.33	2.50–5.00
French lavender	4.17	2.50–5.00	4.17	2.50–5.00
Rosewood	4.17	2.50–5.00	4.17	2.50–5.00
PC3	5.00	5.00	4.17	2.50–5.00
Spruce	8.33	5.00–10.00	5.42	1.25–10.00
White fir	10.00	10.00	8.33	5.00–10.00

T1 = Thieves; E2 = Exodus II; PC3 = Peace & Calming; TW4 = T. Wood (see Table 1).

^a.As determined by the lack of INT reduction to INT formazan; n = 3 for each oil.

^b.As determined by OD readings at 600 nm; n = 3 for each oil.

Table 4.. Zones of inhibition for diffusion assays against Staphylococcus aureus. and Candida albicans..

	Staphylococcus aureus.				Candida albicans.
	Disk difusion		Hole-plate		Disk diffusion		Hole-plate
Essential oil		SE		SE		SE		SE
Thyme	15.58	±0.51	14.58	±1.16	31.67	±0.98	21.37	±0.60
Turkish oregano	13.08	±0.24	12.50	±0.61	21.17	±0.91	18.67	±2.74
Melissa	12.00	±0.89	6.92	±0.20	30.00	±0.37	14.25	±029
Mountain savory	11.33	±1.17	9.33	±0.84	26.00	±2.06	18.42	±0.84
E2	9.17	±0.11	9.67	±0.46	18.08	±0.80	15.50	±0.56
T1	4.38	±0.17	4.92	±0.58	12.33	±1.35	9.58	±0.99
Rosewood	4.00	±0.51	5.83	±0.54	20.00	±1.16	19.33	±1.10
TW4	3.25	±0.51	4.00	±0.26	6.67	±0.69	5.17	±0.75
French lavender	2.17	±0.51	2.17	±0.64	6.58	±0.68	2.58	±0.58
Idaho tansy	1.33	±0.51	3.08	±0.24	2.75	±0.20	2.33	±0.24
Tarragon	1.00	±0.51	2.08	±0.08	4.08	±0.16	3.83	±0.12
Spruce	1.00	±0.51	1.33	±0.42	1.50	±0.58	0.00	±0.00
White fir	0.67	±0.51	2.67	±0.25	1.92	±0.32	1.42	±0.54
PC3	0.33	±0.51	2.33	±0.11	2.29	±0.84	2.17	±0.90

T1 = Thieves; E2 = Exodus II; PC3 = Peace & Calming; TW4 = T. Wood (see Table 1).

^a.Zone radius reported in millimeters±one standard error.

Figure 2 Correlation between disk and hole-plate diffusion assay results for Staphylococcus aureus. (A) and Candida albicans. (B).

Figure 3 Correlation between the minimum inhibitory concentration as measured by the INT method and zones of inhibition from the disk diffusion method for Staphylococcus aureus. (A) and Candida albicans. (B).