In vitro synergistic effect of Hibiscus sabdariffa aqueous extract in combination with standard antibiotics against Helicobacter pylori clinical isolates

Figures & data

Table 1. In vitro antibacterial activity of CLA, AMX, MTZ and AEHS against HP strains.

	MIC (μg/mL)
HP strains	CLA	AMX	MTZ	AEHS
HP (ATCC 6583)	16.21	13.50	2.24	12.25
HP01^a	12.56	12.41	13.54	16.68
HP02^a	9.15	13.85	4.59	15.24
HP03^a	10.56	16.89	11.99	9.18
HP04^a	10.98	13.69	10.17	12.81
HP05^a	14.23	12.88	10.97	13.56
HP06^a	10.49	14.73	13.12	14.17

MIC, minimum inhibitory concentration; the values are expressed as an average from three independent experiments, each performed in triplicate. HP, Helicobacter pylori; ATCC, American Type Culture Collection; AEHS, the aqueous extract of H. sabdariffa; CLA, clarithromycin; AMX, amoxicillin; MTZ, metronidazole.

^a Clinical isolates.

Table 2. In vitro combinatory antibacterial effect of AEHS with CLA or MTZ against HP strains.

	AEHS with CLA at following concentrations (μg/mL)								AEHS with MTZ at following concentrations (μg/mL)
	5		3		1		0.5		5		3		1		0.5
HP strains	MIC	∑FIC	MIC	∑FIC	MIC	∑FIC	MIC	∑FIC	MIC	∑FIC	MIC	∑FIC	MIC	∑FIC	MIC	∑FIC
HP (ATCC 6583)	22.23	1.27	19.23	3.13	0.35	0.28	9.45	2.93	13.56	3.12	16.34	2.12	12.34	1.99	12.23	1.27
HP01^a	21.45	2.13	16.24	3.78	12.34	1.72	9.23	3.15	13.32	3.18	12.43	2.23	13.12	3.15	0.34	0.34
HP02^a	17.34	1.98	19.34	2.45	16.34	2.14	15.63	1.98	14.26	2.15	7.43	1.16	9.32	2.45	9.45	1.36
HP03^a	18.56	3.24	20.23	2.16	16.23	3.45	14.65	2.43	17.23	2.87	8.45	1.13	17.32	3.14	0.40	0.39
HP04^a	19.34	2.89	18.45	2.13	13.78	2.45	18.45	3.15	8.34	1.98	8.34	2.84	17.32	2.36	9.45	2.26
HP05^a	17.43	3.14	17.34	1.13	14.67	3.19	19.43	3.48	7.23	1.92	17.43	2.36	16.43	2.73	10.21	1.99
HP06^a	18.34	2.75	18.45	1.78	0.36	0.21	12.45	2.41	8.98	1.23	21.34	2.73	12.98	2.83	21.32	1.78

∑FIC: sum of fractional inhibitory concentrations – the combination interaction is evaluated as follows: synergy ∑FIC ≤ 0.5 (bold font indicates synergistically acting combinations); additive ∑FIC >0.5 and ≤1; no interaction ∑FIC > 1 and ≤4; antagonistic if ∑FIC >4; MIC – bold font indicates fold reductions. MIC, minimum inhibitory concentration; HP, Helicobacter pylori; ATCC, American Type Culture Collection; AEHS, the aqueous extract of H. sabdariffa; CLA, clarithromycin; MTZ, metronidazole.

^a Clinical isolates.

Table 3. In vitro combinatory antibacterial effect of AEHS with AMX against HP strains.

	AEHS with AMX at following concentrations (μg/mL)
	5		3		1		0.5
HP strains	MIC	∑FIC	MIC	∑FIC	MIC	∑FIC	MIC	∑FIC
HP (ATCC 6583)	12.43	1.36	13.12	0.73	13.23	0.62	15.32	0.71
HP01^a	14.25	1.36	12.34	2.13	14.23	2.13	13.24	3.13
HP02^a	13.65	2.36	18.34	0.81	17.44	0.79	14.56	0.92
HP03^a	13.45	2.34	17.34	1.68	17.34	1.95	10.89	1.98
HP04^a	10.89	3.15	15.34	0.78	18.34	0.96	12.34	0.82
HP05^a	15.25	3.98	14.28	0.91	17.36	0.84	8.45	0.87
HP06^a	16.34	3.57	9.78	0.63	16.98	0.61	7.14	0.82

∑FIC: sum of fractional inhibitory concentrations – the combination interaction is evaluated as follows: synergy ∑FIC ≤ 0.5; additive ∑FIC >0.5 and ≤1 (bold font indicates additive acting combinations); no interaction ∑FIC > 1 and ≤4; antagonistic if ∑FIC > 4. MIC, minimum inhibitory concentration; HP, Helicobacter pylori; AEHS, the aqueous extract of H. sabdariffa; ATCC, American Type Culture Collection; AMX, amoxicillin.

^a Clinical isolates.

Table 4. Chemical characterisation of TFC and TAC in AEHS.

TFC (%) calculated as rutin	TAC as mg of cyaniding-3-O-glucoside equivalent (mg/100 g DW)
0.247%	1465.8 mg/100 g DW

TFC, total flavonoid content; TAC, total anthocyanins; DW, dry weight of Hibiscus calyces; AEHS, the aqueous extract of H. sabdariffa.