Table 2.

Analysis of the synergistic activity of the six pure compounds tested as binary combinations (compound A + compound B) against Campylobacter jejuni 11168, in terms of the fractional inhibitory concentration index (FIC_I) calculated from the minimal inhibitory concentrations (MICs) of the pure compounds alone (A_pure, B_pure) and when tested together (A_mix, B_mix). See Equations (1)–(3) for further details.

Combination		MIC (mg/L)				FICi
		Pure Compounds		Mixed Compounds
Compound A	Compound B	Apurea	Bpureb	Amixc	Bmixd
Carvacrol	Thymol	62.5	31.25	7.81	1.95	0.2
	Thymoquinone	62.5	31.25	15.62	7.81	0.5
	p-cymene	62.5	500	62.5	500	2.0
	γ-terpinene	31.25	2000	31.25	2000	2.0
	Rosmarinic acid	31.25	250	31.25	250	2.0
Thymol	Thymoquinone	31.25	31.25	3.9	3.9	0.3
	p-cymene	31.25	31.25	31.25	31.25	2
	γ-terpinene	125	1000	62.5	1000	1.5
	Rosmarinic acid	31.25	250	31.25	250	2
Thymoquinone	p-cymene	15.62	1000	7.81	1000	1.5
	γ-terpinene	31.25	1000	7.81	500	0.8
	Rosmarinic acid	31.25	250	7.81	62.50	0.5
p-cymene	γ-terpinene	250	1000	125	1000	1.5
	Rosmarinic acid	1000	250	500	125	1.0
γ-terpinene	Rosmarinic acid	1000	250	1000	125	1.5

^a—MIC of compound A when tested alone (e.g., carvacrol alone); ^b—MIC of compound B when tested alone (e.g., thymol); ^c—the concentration of compound A in AB mixture (e.g., carvacrol in carvacrol + thymol mixture) at MIC of AB; ^d—the concentration of compound B in AB mixture (e.g., thymol in carvacrol + thymol mixture) at MIC of AB.