Assessment of interactions between 4-HR and various groups of antibiotics against clinical isolates of gram negative pathogenic K. pneumoniae.

The chequerboard method yields FICI values (Eq 1) as well as the coefficient K1 (decrease in the effective dose of antibiotic in the presence of 4-HR; Eq 2). Synergy is defined by FICI ≤ 0.5, absence of interaction by 0.5 ≤ FICI ≤ 4.0, and antagonism by FICI ≥ 4.0. For the resistant pathogen, 4-HR concentrations were 512 μg/L. For the sensitive strain, 4-HR concentrations were 64 μg/L. Unit of MIC is μg/L. MIC AB designates MIC of the antibiotic alone.