Discovery of Schiff base-triazole-pleuromutilin conjugates as broad-spectrum antibacterial agents with potent...

Pleuromutilins effectively inhibit cross-resistance and are valuable therapeutic candidates against multidrug-resistant bacteria, due to their unique ribosomal binding mechanism. However, because of their limited spectrum against Gram-negative bacteria, the emerging resistance necessitates structural optimization. Herein, we report a scaffold conjugation strategy integrating 1,2,4-triazole and Schiff base privileged structures with pleuromutilin to address these limitations. Among the synthesized derivatives, compound T7 demonstrated exceptional broad-spectrum activity, with minimum inhibitory concentrations (MICs) of 0.125-2 μg/mL against clinical MRSA and Enterococcus faecium isolates, which were superior to those of the clinically used antibiotic retapamulin. Remarkably, T7 also exhibited potent activity against Gram-negative bacteria, thereby overcoming the limited spectrum of pleuromutilins. Mechanistic investigations revealed that T7 disrupted bacterial biofilms and cell membrane integrity. Transcriptomic analysis unveiled its multimodal mechanism of action against MRSA, encompassing inhibition of ATP-binding cassette (ABC) transporters, impairment of the phosphotransferase system (PTS), ribosomal binding, and attenuation of virulence and adhesion factors. Metabolomic profiling and q-PCR analysis consistently supported these transcriptomic findings. Furthermore, T7 displayed minimal hemolytic activity and demonstrated significant in vivo efficacy in a Caenorhabditis elegans MRSA infection model. Collectively, these findings establish T7 as a highly promising broad-spectrum antibiotic candidate with a distinctive mechanism for combating multidrug-resistant pathogens, particularly MRSA.