In vitro activity of colistin in combination with various antimicrobials against Acinetobacter baumannii species, a report from South Iran

Figures & data

Table 1 The minimum inhibitory concentration (MIC) values (mcg/mL) obtained using E-test method of antimicrobial agents against 20 Acinetobacter baumannii samples isolated from blood cultures of patients admitted to intensive care units of Nemazee Hospital

Sample	MIC
	Rifampin	Ciprofloxacin	Levofloxacin	Imipenem	Meropenem	Ampicillin–sulbactam	Colistin
1	1	0.2	0.5	2	0.009	0.009	0.25
2	1	0.256	16	2	0.18	6	0.5
3	1	0.4	0.05	8	0.025	2	0.125
4	0.5	0.125	0.06	1	0.03	3	0.25
5	1	0.2	0.05	8	0.015	1	0.25
6	4	64	8	8	0.18	6	0.125
7	4	128	32	8	0.25	4	0.25
8	1	0.25	1	0.625	0.03	1	0.18
9	1	0.5	0.03	2	0.015	0.5	1
10	1	0.064	0.128	8	0.19	1.5	0.06
11	1	0.188	0.094	4	0.19	0.75	0.25
12	16	1	0.5	8	0.025	6	0.375
13	2	128	6	0.15	0.09	2	1
14	0.5	0.095	0.76	8	0.015	1	0.18
15	1	64	8	8	8	12	0.25
16	2	32	64	24	8	64	0.19
17	1.5	64	32	48	32	64	0.375
18	8	64	8	32	32	16	0.5
19	0.5	128	8	16	8	24	0.093
20	>128	32	2	32	32	64	0.06

Table 2 Checkerboard synergy study results for the combinations of colistin with six different antibiotics (rifampin, ciprofloxacin, levofloxacin, imipenem, meropenem, ampicillin–sulbactam) tested against 20 samples of Acinetobacter Baumannii strains isolated from blood cultures of patients admitted to intensive care units of Nemazee Hospital

Sample	Combination of antibiotics with colistin
	Rifampin		Ciprofloxacin		Levofloxacin		Imipenem		Meropenem		Ampicillin–sulbactam
	FICI	Result	FICI	Result	FICI	Result	FICI	Result	FICI	Result	FICI	Result
1	0.75	part	0.62	part	0.37	syn	2.5	anta	1	ind	1	ind
2	0.75	part	1	ind	1	ind	0.5	syn	1	ind	1	ind
3	0.49	syn	0.07	syn	2.5	anta	1	ind	2.5	anta	1.5	ind
4	0.62	part	0.56	part	2	anta	1	ind	2.5	anta	1	ind
5	0.37	syn	0.75	part	2	anta	2.007	anta	0.75	part	1.5	ind
6	0.6	part	0.56	part	0.74	part	2.5	anta	2.5	anta	1	ind
7	0.5	syn	4.25	anta	2	anta	2.5	anta	1	ind	0.75	part
8	0.37	syn	1.25	ind	1	ind	0.75	part	2.5	anta	0.375	syn
9	0.5	syn	0.5	syn	2	anta	3	anta	1	ind	0.31	syn
10	0.37	syn	2	anta	0.75	part	1	ind	1	ind	2.5	anta
11	0.31	syn	2.06	anta	1	ind	1	ind	3	anta	2.5	anta
12	0.25	part	1	ind	2	anta	2.06	anta	2.25	anta	1	ind
13	0.625	part	2.125	anta	4	anta	2	anta	1	ind	0.5	syn
14	0.5	syn	0.5	syn	2	anta	2.5	anta	0.75	part	1.25	ind
15	0.37	syn	1	ind	0.62	part	0.37	syn	0.62	part	1.5	ind
16	0.75	part	1	ind	2	anta	0.5	syn	0.55	part	1	ind
17	0.3	syn	3	anta	0.55	part	0.5	syn	0.55	part	0.75	part
18	1	ind	0.75	part	2	anta	0.75	part	0.37	syn	1	ind
19	0.75	part	1	ind	4.5	anta	1.5	ind	1	ind	1	ind
20	0.24	syn	2.58	anta	1	ind	0.625	part	0.37	syn	2.3	anta

Abbreviations: anta, antagonist; FICI, fractional inhibitory concentration index; ind, indifference; part, partial synergy; syn, synergy.

Table 3 Results of the checkerboard synergy test of combination of colistin with six different antibiotics against 20 strains of Acinetobacter baumannii isolated from blood cultures of patients admitted to intensive care units of Nemazee Hospital

	Result
Combination	Synergy	Partial synergy	Indifference	Antagonist
Colistin + rifampin	55%	40%	5%	0%
Colistin + imipenem	20%	15%	25%	40%
Colistin + ciprofloxacin	15%	25%	30%	30%
Colistin + ampicillin–sulbactam	15%	10%	60%	15%
Colistin + meropenem	10%	25%	35%	30%
Colistin + levofloxacin	5%	20%	65%	10%