Palmatine potentiates cefquinome against multidrug resistant Escherichia coli via sulfur/taurine metabolism and oxidative stress

Yining ZhangYinchao TongPengcheng LiLeixin ZhuHao ZhangHonglin XieSaba NasirWei LiMingjin FangJuan WangSuzhu Qing^*Xinglong Wang^*Weimin Zhang^*

• Northwest A&F University, Xianyang, China

Palmatine, a natural isoquinoline alkaloid derived from Fibraureae Caulis, is widely used for clearing heat and detoxification, inhibiting bacteria, and reducing inflammation. The emergence of multidrug resistance in Escherichia coli poses a critical challenge to β-lactam efficacy, particularly against cephalosporins like cefquinome. This study demonstrates that palmatine potently enhances the activity of cefquinome through multi-targeted mechanisms, revealing a new pharmacological application. Antimicrobial and synergy activity was assessed using the micro broth dilution method and checkerboard assay. Morphology was observed using SEM, and the laser confocal microscope was using to observe the biofilm inhibition. Membrane damage and reactive oxygen species were determined by fluorescent probe dyes. Transcriptome and RT-qPCR analysis were detected key mechanism pathways. The synergistic effect was evaluated through the mouse Escherichia coli infection model. In vitro, analyses of 20 tested isolates revealed a broad synergistic effect (FICI ≤0.5), reducing cefquinome MICs by 4-32 fold. Mechanistic investigations uncovered palmatine's capacity to disrupt membrane integrity, potentiates oxidative stress, and inhibits biofilm formation. Transcriptomic profiling identified sulfur metabolism as the implicated pathway, with palmatine reversing cefquinome-induced downregulation of sulfur metabolism genes. Functional validation confirmed interference with taurine uptake in the sulfur metabolic pathway could eliminate the synergistic effect. In murine infection models, combination therapy enhanced survival by 30% and alleviated diarrhoea while decreasing tissue bacterial loads. This work discovers the novel pharmacological effects of palmatine, establishes metabolic level reversal regulation as a novel strategy to combat β-lactam resistance, positioning palmatine as a multi-target adjuvant for cefquinome against resistant Gram-negative infections.