Integrated Transcriptomic and Metabolomic Analyses Reveal the Antibacterial Mechanism of Isocorydine against Mycobacterium bovis

Mycobacterium bovis, the causative agent of bovine tuberculosis, poses a significant zoonotic threat. This study defines the antibacterial activity and mechanism of the natural alkaloid isocorydine (ICD) against M. bovis using an integrated multi-omics approach. Phenotypic analyses demonstrated that ICD (MIC=400 μg/mL) disrupts cell wall and membrane integrity, causing ion leakage, extracellular pH alteration, lipid depletion, and severe ultrastructural damage. Transcriptomic profiling under sub-inhibitory ICD stress revealed 66 differentially expressed genes, with significant upregulation of efflux pumps (ABC transporters, MMPL, SMR) and their associated TetR family transcriptional regulators, indicating a targeted bacterial counter-response. Concurrently, metabolomic analysis identified 1,158 differential metabolites, depicting a state of profound metabolic dysregulation characterized by the depletion of central carbon metabolites (e.g., sugars, succinate) and the accumulation of fatty acids and precursors (e.g., oleic acid). Integrated pathway analysis highlighted critical disruptions in starch/sucrose metabolism, ABC transporters, and fatty acid biosynthesis. Our findings establish that ICD exerts its bactericidal effect primarily by targeting the cell envelope, causing irreparable physical damage and triggering a catastrophic metabolic crisis that overwhelms the bacterium's compensatory mechanisms. This work elucidates a multi-targeted antibacterial mechanism and positions ICD as a promising phytochemical lead for combating mycobacterial infections.