Mechanism of action of, and mechanism of reduced susceptibility to the novel anti-Clostridium difficile compound LFF571

LFF571 is a novel semi-synthetic analog of the thiopeptide natural product GE2270 A and a potent inhibitor of Gram-positive aerobic and anaerobic bacteria. The parent compound is a translational inhibitor that binds elongation factor Tu (EF-Tu) and blocks its function. Here we report an analogous mechanism of action for LFF571 against Clostridium difficile. In exponentially growing cultures, LFF571 inhibited protein synthesis with an IC50 of 0.06 µg/ml. We also determined the frequency and mechanism of reduced susceptibility to the compound in vitro. Single-step, spontaneous mutants of C. difficile were selected on super-inhibitory concentrations of LFF571 at a frequency of