Small Molecule IITR00693 (2-Aminoperimidine) Synergizes Polymyxin B Activity against <i>Staphylococcus aureus</i> and <i>Pseudomonas aeruginosa</i>

The rise of antibiotic resistance among skin-infecting pathogens poses an urgent threat to public health and has fueled the search for new therapies. Enhancing the potency of currently used antibiotics is an alternative for the treatment of infections caused by drug-resistant pathogens. In this study, we aimed to identify a small molecule that can potentiate currently used antibiotics. IITR00693 (2-aminoperimidine), a novel antibacterial small molecule, potentiates the antibacterial activity of polymyxin B against Staphylococcus aureus and Pseudomonas aeruginosa. Herein, we investigated in detail the mode of action of this interaction and the molecule's capability to combat soft-tissue infections caused by S. aureus and P. aeruginosa. A microdilution checkerboard assay was performed to determine the synergistic interaction between polymyxin B and IITR00693 in clinical isolates of S. aureus and P. aeruginosa. Time-kill kinetics, post-antibiotic effect, and resistance generation studies were performed to assess the pharmacodynamics of the combination. Assays based on different fluorescent probes were performed to decipher the mechanism of action of this combination. The in vivo efficacy of the IITR00693-polymyxin B combination was determined in a murine acute wound infection model. IITR00693 exhibited broad-spectrum antibacterial activity. IITR00693 potentiated polymyxin B and colistin against polymyxin-resistant S. aureus. IITR00693 prevented the generation of resistant mutants against multiple antibiotics. The IITR00693-polymyxin B combination decreased the S. aureus count by >3 log10 CFU in a murine acute wound infection model. IITR00693 is a potential and promising candidate for the treatment of soft-tissue infections along with polymyxins.