In Vitro Synergistic Activity of Combinations of Tetrahydroisoquinolines and Treatment Antibiotics against Multidrug-Resistant Salmonella
Table 1
Minimum inhibitory concentrations (MICs) and fractional inhibitory concentration indices (FICIs) showing effects of antibiotics in combination with THIQs.
Combination (THIQ/antibiotic)
MIC (μg/mL)
MIC fold change (antibiotic)
FICc
FICa
FICI
Outcome
MIC alone
MIC combined
1/AMP
16/256
1/16
−16
0.0625
0.0625
0.125
Synergism
2/AMP
64/256
32/256
−1
0.5
1.0
1.5
Indifferent
3/AMP
256/256
64/256
−1
0.25
1.0
1.25
Indifferent
4/AMP
16/256
4/128
−2
0.25
0.5
0.75
Additive
5/AMP
256/256
256/256
−1
1.0
1.0
2.0
Indifferent
1/CHL
16/128
1/2
−64
0.0625
0.0156
0.078
Synergism
2/CHL
64/128
64/128
−1
1.0
1.0
2.0
Indifferent
3/CHL
256/128
128/128
−1
0.5
1.0
1.5
Indifferent
4/CHL
16/128
4/64
−2
0.25
0.5
0.75
Additive
5/CHL
256/128
64/128
−1
0.25
1.0
1.25
Indifferent
1/SXT
16/256
2/4
−64
0.125
0.0156
0.141
Synergism
2/SXT
64/256
64/256
−1
1.0
1.0
2.0
Indifferent
3/SXT
256/256
16/8
−32
0.0625
0.03125
0.094
Synergism
4/SXT
16/256
4/128
−2
0.25
0.5
0.75
Additive
5/SXT
256/256
64/64
−4
0.25
0.25
0.5
Synergism
1/CIP
16/16
2/8
−2
0.5
0.125
0.625
Additive
2/CIP
64/16
4/2
−16
0.0625
0.125
0.188
Synergism
3/CIP
256/16
128/64
+4
0.5
4.0
4.5
Antagonism
4/CIP
16/16
4/4
−4
0.25
0.25
0.5
Synergism
5/CIP
256/16
64/64
+4
0.25
4.0
4.25
Antagonism
THIQs: 1, 2, 3, 4, and 5; antibiotics: AMP, ampicillin; CHL, chloramphenicol; SXT: sulphamethoxazole-trimethoprim; CIP: ciprofloxacin; FICa: fractional inhibitory concentration of antibiotic; FICc: fractional inhibitory concentration of compound; FICI: fractional inhibitory concentration index; −: MIC reduction; +: increase in MIC.
