The minimum inhibitory concentrations (MIC) of two antibiotics against a bacterial strain are: $ \text{MIC}_{X}=8\ \mu\text{g mL}^{-1} $ and $ \text{MIC}_{Y}=2\ \mu\text{g mL}^{-1} $. When used in combination, the MICs are reduced to $ \text{MIC}_{X,\text{comb}}=2\ \mu\text{g mL}^{-1} $ and $ \text{MIC}_{Y,\text{comb}}=0.5\ \mu\text{g mL}^{-1} $. Calculate the Fractional Inhibitory Concentration Index (FICI) and state whether the interaction is synergistic, additive, indifferent or antagonistic (use the standard interpretation: synergistic ≤ 0.5, additive  0.5-1.0, indifferent  1.0-4.0, antagonistic  4.0).

Question

The minimum inhibitory concentrations (MIC) of two antibiotics against a bacterial strain are: $ \text{MIC}_{X}=8\ \mu\text{g mL}^{-1} $ and $ \text{MIC}_{Y}=2\ \mu\text{g mL}^{-1} $. When used in combination, the MICs are reduced to $ \text{MIC}_{X,\text{comb}}=2\ \mu\text{g mL}^{-1} $ and $ \text{MIC}_{Y,\text{comb}}=0.5\ \mu\text{g mL}^{-1} $. Calculate the Fractional Inhibitory Concentration Index (FICI) and state whether the interaction is synergistic, additive, indifferent or antagonistic (use the standard interpretation: synergistic ≤ 0.5, additive > 0.5-1.0, indifferent > 1.0-4.0, antagonistic > 4.0).

Accepted Answer

FICI = 0.5; the interaction is synergistic

Gce Model Questions Vol1 2025 Biology Question 50

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