Thiazolopyrimidinone Derivative H5–23 Enhances Daptomycin Activity against Linezolid-Resistant Enterococcus faecalis by Disrupting the Cell Membrane

The increasing emergence and dissemination of multidrug-resistant (MDR) Gram-positive pathogens pose a serious threat to global public health. Previous reports have demonstrated that the compound H5–23, which has a thiazolopyrimidinone core structure, exhibited antibacterial activity against Staphylococcus epidermidis in vitro. However, the antibacterial activity in vivo and mechanism of action of H5–23 against MDR bacteria have not been fully studied. In this study, we report that H5–23 has wide-spectrum antibacterial activity against Gram-positive bacteria. When combined with daptomycin (DAP), H5–23 demonstrates enhanced antimicrobial activity, effectively killing both planktonic and persister cells, as well as eradicating biofilm formation by linezolid-resistant Enterococcus faecalis. The development of resistance shows that H5–23 has a low propensity to induce antibiotic resistance compared to that of linezolid in vitro. Mechanistic studies reveal that H5–23 increases membrane permeability and disrupts membrane integrity, resulting in increased production of reactive oxygen species (ROS), metabolic perturbations, and ultimately cell death. Additionally, we demonstrate the synergistic antibacterial effect of H5–23 combined with DAP in a murine model. These findings suggest that H5–23 is a promising antimicrobial agent and provides a potential strategy for enhancing the efficacy of DAP in combating multidrug-resistant E. faecalis.