Antimicrobial Susceptibility among Colistin, Sulbactam, and Fosfomycin and a Synergism Study of Colistin in Combination with Sulbactam or Fosfomycin against Clinical Isolates of Carbapenem-Resistant Acinetobacter baumannii
Table 2
Antimicrobial combination test against carbapenem-resistant A. baumannii clinical isolates using chequerboard technique.
Strains
REP-PCR group
Colistin + sulbactam
Colistin + fosfomycin
FICI (Col)
FICI (Sul)
ΣFICI (Col + Sul)
Interpretation (Col + Sul)
FICI (Col)
FICI (Fos)
ΣFICI (Col + Fos)
Interpretation (Col + Fos)
AB 1
A
0.06
2
2.06
Indifference
0.5
0.5
1
Additive
AB 2
A
0.25
0.5
0.75
Additive
0.5
0.13
0.63
Additive
AB 4
A
0.13
0.25
0.38
Synergism
0.5
0.25
0.75
Additive
AB 6
A
0.5
0.06
0.56
Additive
0.5
0.25
0.75
Additive
AB 7
A
0.25
0.25
0.5
Synergism
0.25
0.13
0.38
Synergism
AB 13
A
0.13
0.5
0.63
Additive
0.13
1
1.13
Indifference
AB 14
A
0.5
0.5
1
Additive
0.5
0.5
1
Additive
AB 15
A
0.03
1
1.03
Indifference
0.13
0.25
0.38
Synergism
AB 3
B
0.5
0.5
1
Additive
1
0.25
1.25
Indifference
AB 5
C
0.13
1.0
1.13
Indifference
0.25
0.25
0.5
Synergism
AB 8
D
0.06
1
1.06
Indifference
0.25
0.5
0.75
Additive
AB 9
E
0.008
1
1.01
Indifference
0.03
0.25
0.28
Synergism
AB 10
F
0.004
2
2.00
Indifference
0.02
1
1.02
Indifference
AB 11
G
1
0.004
1.004
Indifference
0.01
1
1.01
Indifference
AB 12
H
0.06
0.5
0.56
Additive
0.25
0.5
0.75
Additive
The fractional inhibitory concentration indices (FICI) were interpreted as ≤0.5 = synergistic, >0.5–<1.0 = additive effect, >1–4 = indifference, and ≥4 antagonistic effect.
