When Combined with Colistin, an Otherwise Ineffective Rifampicin-Linezolid Combination Becomes Active in and .

The synergistic action of colistin, with two antibiotics active in Gram-positive bacteria but unable to kill gram negatives (linezolid and rifampicin), was investigated, since triple combinations are emerging as a tool to overtake multidrug resistance. Checkerboard determinations demonstrated that, when combined with colistin, the combination of linezolid and rifampicin turns active in multidrug-resistant and . Thus, the presence of sublethal concentrations of colistin resulted in a strongly synergistic interaction between these two drugs.