Synergistic antimicrobial activity of two binary combinations of marjoram, lavender, and wild thyme essential oils

Figures & data

Table 1. Chemical composition of Lavendula dentata essential oil by GC/MS analysis.

Compounds	RT (min)	RI	Peak area %
Tricyclene	5.24	922	0.23
1R-α-Pinene	5.49	932	8.40
Camphene	5.93	948	1.12
Benzaldehyde	6.02	952	0.22
β-Sabinene	6.53	971	1.24
β-Pinene	6.70	977	25.82
β-Myrcene	6.96	987	0.41
Cymene	8.13	1023	0.65
D-Limonene	8.29	1028	3.35
1,8-Cineole	8.40	1031	10.82
Artemisia ketone	9.30	1056	0.10
Endo-5-norbornene-2-methanol	9.75	1069	0.19
Camphenilone	10.27	1083	0.05
Linalool oxide	10.35	1085	0.20
Fenchone	10.45	1088	9.87
Linalool	10.85	1099	0.85
Exo-fenchol	11.65	1119	3.36
trans-p-mentha-2,8-dien-1-ol	11.84	1124	0.20
α-campholenal	11.92	1126	0.48
Cyclohexyl propanoate	12.07	1129	0.19
Nopinone	12.40	1137	1.54
trans-verbenol	12.50	1140	5.95
Camphor	12.75	1146	4.18
Camphene hydrate	12.88	1149	0.24
Iso-borneol	13.16	1156	0.26
Pinocarvone	13.35	1161	0.57
Borneol	13.79	1171	2.30
cis-Pinocamphone	13.86	1173	0.05
3-(1H-Imidazol-4-yl)-propan-1-ol	13.89	1174	0.06
Iso-menthol	14.13	1179	0.69
Cryptone	14.28	1183	0.26
3-Decanone	14.37	1185	1.38
Myrtenal	14.74	1194	6.98
cis-Verbenone	15.21	1206	0.43
2E,4E-Nonadienol	15.74	1218	0.44
Anisaldehyde	16.70	1241	0.39
Carvone	16.75	1242	0.46
Perrilaldehyde	18.10	1273	0.07
p-Cymen-7-ol	18.84	1291	0.15
p-Menth-1-en-9-ol	19.14	1298	0.07
Exo-2-ethyl-fenchol	19.15	1298	0.05
Neo-8-hydroxy-menthol	20.62	1333	0.13
Iso-gamma-E-bisabolene	24.65	1528	0.19
Pigmaein	26.87	1484	0.35
Bisabolene	27.69	1504	0.18
Geranyl isovalerate	27.77	1506	0.24
E-isoeugenol acetate	28.13	1516	0.27
2E-hexenyl phenyl acetate	28.98	1538	0.56
Epi-alpha-cadinol	29.07	1540	0.23
Selina-3,11-dien-6alpha-ol	29.26	1545	0.05
Cyclooctane, 1,5-dimethyl-2,6-bis(methylene)-	30.48	1576	0.28
β-Eudesmol	33.26	1650	0.86
E-bisabol-11-ol	33.93	1668	0.16
cis-methyl epi-jasmonate	34.30	1678	0.57
E-methyl-dihydro-jasmonate	34.46	1682	0.29
2E,6E-farnesol	36.68	1744	1.26
Monoterpenes			94.41
Sesquiterpenes			5.49
Total			99.90

RT: retention time; RI: retention index.

Table 2. Minimal inhibitory concentration of O. majorana, L. dentata essential, and T. serpyllum oils against S. aureus and E. coli.

	Staphylococcus aureus			Escherichia coli
Concentration % (v/v)	O. m	L. d	T. s	O. m	L. d	T. s
4	*	*	-	-	-	-
2	-	-	-	-	+	-
1	-	-	-	-	+	-
0.5	-	+	-	-	+	-
0.25	-	+	-	-	+	-
0.125	+	+	+	+	+	-
0.0625	+	+	+	+	+	+
0.03125	+	+	+	+	+	+
0.01562	+	*	+	+	*	+

+: presence of growth; -: absence of growth; *: not done; O. m: O. majorana, L. d: L. dentata, T. s: thymus serpyllum; (v/v): (oil volume/medium volume).

Table 3. Minimum bactericidal concentration values of O. majorana and L. dentata and T. serpyllum essential oil against S. aureus and E. coli.

	Staphylococcus aureus ATCC 29213			Escherichia coli ATCC 25922
Concentration % (v/v)	O. m	L. d	T.s	O. m	L. d	T.s
4	-	-	-	-	+	-
2	-	-	-	-	+	-
1	+	-	-	-	*	-
0.5	+	+	-	-	*	-
0.25	+	*	-	-	*	-
0.125	*	*	*	*	*	+

+: presence of growth; -: absence of growth; *: not done; O. m: O. majorana, L. d: L. dentata, T. s: thymus serpyllum; (v/v): (oil volume/medium volume).

Table 4. Fractional inhibitory concentration (FIC) index and outcome of interaction of O. majorana and L. dentata essential oil combination against S. aureus and E. coli.

Bacteria strains	Part of Plant	MIC alone % (v/v)	MIC combination % (v/v)	Oils combination	FIC % (v/v)	FIC index	Outcome
Staphylococcus aureus ATCC 29213	L. dentata	1	0.125	L. dentata/O. majorana	0.125	0.625	Partial synergy
	O. majorana	0.25	0.125		0.5
	L. dentata	1	0.5		0.5	1	Additive
	O. majorana	0.25	0.125		0.5
Escherichia coli ATCC 25922	L. dentata	4	1	L. dentata/O. majorana	0.25	0.75	Partial synergy
	O. majorana	0.25	0.125		0.5
	L. dentata	4	2		0.5	0.75	Partial synergy
	O. majorana	0.25	0.0625		0.25

MIC: Minimal inhibitory concentration; (v/v): (oil volume/medium volume).

Table 5. Fractional inhibitory concentration (FIC) index and outcome of interaction of O. majorana and T. serpyllum essential oil combination against S. aureus and E. coli.

Bacteria strains	Part of Plant	MIC alone % (v/v)	MIC combination % (v/v)	Oils combination	FIC % (v/v)	FIC index	Outcome
Staphylococcus aureus ATCC 29213	T. serpyllum	0.25	0.125	T. serpyllum/O. majorana	0.5	0.75	Partial synergy
	O. majorana	0.25	0.0625		0.25
	T. serpyllum	0.25	0.0625		0.25	0.75	Partial synergy
	O. majorana	0.25	0.125		0.5
Escherichia coli ATCC 25922	T. serpyllum	0.125	0.0625	T. serpyllum/O. majorana	0.5	0.75	Partial synergy
	O. majorana	0.25	0.0625		0.25

MIC: Minimal inhibitory concentration; (v/v): (oil volume/medium volume).